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Sample records for first-principles density functional

  1. Dispersion correction derived from first principles for density functional theory and Hartree-Fock theory.

    Science.gov (United States)

    Guidez, Emilie B; Gordon, Mark S

    2015-03-12

    The modeling of dispersion interactions in density functional theory (DFT) is commonly performed using an energy correction that involves empirically fitted parameters for all atom pairs of the system investigated. In this study, the first-principles-derived dispersion energy from the effective fragment potential (EFP) method is implemented for the density functional theory (DFT-D(EFP)) and Hartree-Fock (HF-D(EFP)) energies. Overall, DFT-D(EFP) performs similarly to the semiempirical DFT-D corrections for the test cases investigated in this work. HF-D(EFP) tends to underestimate binding energies and overestimate intermolecular equilibrium distances, relative to coupled cluster theory, most likely due to incomplete accounting for electron correlation. Overall, this first-principles dispersion correction yields results that are in good agreement with coupled-cluster calculations at a low computational cost.

  2. First-principle study of nanostructures of functionalized graphene

    Indian Academy of Sciences (India)

    We present first-principle calculations of 2D nanostructures of graphene functionalized with hydrogen and fluorine, respectively, in chair conformation. The partial density of states, band structure, binding energy and transverse displacement of C atoms due to functionalization (buckling) have been calculated within the ...

  3. Density functional studies: First principles and semiempirical calculations of clusters and surfaces

    International Nuclear Information System (INIS)

    Sinnott, S.B.

    1993-01-01

    In the research presented here, various theoretical electronic structure techniques are utilized to analyze widely different systems from silicon clusters to transition metal solids and surfaces. For the silicon clusters, first principles density functional methods are used to investigate Si N for N = 2-8. The goal is to understand the different types of bonding that can occur in such small clusters where the coordination of the atoms differs substantially from that of the stable bulk tetrahedral bonding. Such uncoordinated structures can provide a good test of more approximate theories that can be used eventually to model silicon surfaces, of obvious technological importance. For the transition metal systems, non-self-consistent electronic structure methods are used to provide an understanding of the driving force for surface relaxations. An in-depth analysis of the results is presented and the physical basis of surface relaxation within the theory is discussed. In addition, the limitations inherent in calculations of metal surface relaxation are addressed. Finally, in an effort to increase understanding of approximate methods, a novel non-self-consistent density functional electronic structure method is developed that is ∼1000 times faster computationally than more sophisticated methods. This new method is tested for a variety of systems including diatomics, mixed clusters, surfaces and bulk lattices. The strengths and weaknesses of the new theory are discussed in detail, leading to greater understanding of non-self-consistent density functional theories as a whole

  4. Ground-state densities from the Rayleigh-Ritz variation principle and from density-functional theory.

    Science.gov (United States)

    Kvaal, Simen; Helgaker, Trygve

    2015-11-14

    The relationship between the densities of ground-state wave functions (i.e., the minimizers of the Rayleigh-Ritz variation principle) and the ground-state densities in density-functional theory (i.e., the minimizers of the Hohenberg-Kohn variation principle) is studied within the framework of convex conjugation, in a generic setting covering molecular systems, solid-state systems, and more. Having introduced admissible density functionals as functionals that produce the exact ground-state energy for a given external potential by minimizing over densities in the Hohenberg-Kohn variation principle, necessary and sufficient conditions on such functionals are established to ensure that the Rayleigh-Ritz ground-state densities and the Hohenberg-Kohn ground-state densities are identical. We apply the results to molecular systems in the Born-Oppenheimer approximation. For any given potential v ∈ L(3/2)(ℝ(3)) + L(∞)(ℝ(3)), we establish a one-to-one correspondence between the mixed ground-state densities of the Rayleigh-Ritz variation principle and the mixed ground-state densities of the Hohenberg-Kohn variation principle when the Lieb density-matrix constrained-search universal density functional is taken as the admissible functional. A similar one-to-one correspondence is established between the pure ground-state densities of the Rayleigh-Ritz variation principle and the pure ground-state densities obtained using the Hohenberg-Kohn variation principle with the Levy-Lieb pure-state constrained-search functional. In other words, all physical ground-state densities (pure or mixed) are recovered with these functionals and no false densities (i.e., minimizing densities that are not physical) exist. The importance of topology (i.e., choice of Banach space of densities and potentials) is emphasized and illustrated. The relevance of these results for current-density-functional theory is examined.

  5. Effect of Interface Structure on Thermal Boundary Conductance by using First-principles Density Functional Perturbation Theory

    Institute of Scientific and Technical Information of China (English)

    GAO Xue; ZHANG Yue; SHANG Jia-Xiang

    2011-01-01

    We choose a Si/Ge interface as a research object to investigate the infiuence of interface disorder on thermal boundary conductance. In the calculations, the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials, while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory. The results show that interface disorder limits thermal transport. The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance. This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.%We choose a Si/Ge interface as a research object to investigate the influence of interface disorder on thermal boundary conductance.In the calculations,the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials,while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory.The results show that interface disorder limits thermal transport.The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance.This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.It is well known that interfaces can play a dominant role in the overall thermal transport characteristics of structures whose length scale is less than the phonon mean free path.When heat flows across an interface between two different materials,there exists a temperature jump at the interface.Thermal boundary conductance (TBC),which describes the efficiency of heat flow at material interfaces,plays an importance role in the transport of thermal energy in nanometerscale devices,semiconductor superlattices,thin film multilayers and nanocrystalline materials.[1

  6. First-principle study of quantum confinement effect on small sized silicon quantum dots using density-functional theory

    International Nuclear Information System (INIS)

    Anas, M. M.; Othman, A. P.; Gopir, G.

    2014-01-01

    Density functional theory (DFT), as a first-principle approach has successfully been implemented to study nanoscale material. Here, DFT by numerical basis-set was used to study the quantum confinement effect as well as electronic properties of silicon quantum dots (Si-QDs) in ground state condition. Selection of quantum dot models were studied intensively before choosing the right structure for simulation. Next, the computational result were used to examine and deduce the electronic properties and its density of state (DOS) for 14 spherical Si-QDs ranging in size up to ∼ 2 nm in diameter. The energy gap was also deduced from the HOMO-LUMO results. The atomistic model of each silicon QDs was constructed by repeating its crystal unit cell of face-centered cubic (FCC) structure, and reconstructed until the spherical shape obtained. The core structure shows tetrahedral (T d ) symmetry structure. It was found that the model need to be passivated, and hence it was noticed that the confinement effect was more pronounced. The model was optimized using Quasi-Newton method for each size of Si-QDs to get relaxed structure before it was simulated. In this model the exchange-correlation potential (V xc ) of the electrons was treated by Local Density Approximation (LDA) functional and Perdew-Zunger (PZ) functional

  7. First-principles nonlocal-pseudopotential approach in the density-functional formalism: Development and application to atoms

    International Nuclear Information System (INIS)

    Zunger, A.; Cohen, M.L.

    1978-01-01

    We present a method for obtaining first-principles nonlocal atomic pseudopotentials in the density-functional formalism by direct inversion of the pseudopotential eigenvalue problem, where the pseudo-wave-functions are represented as a unitary rotation of the exact all-electron wave functions. The usual pseudopotential nonuniqueness of the orbitals is fixed by imposing the physically appealing constraints of maximum similarity to the all-electron wave functions and minimum radial kinetic energy. These potentials are shown to yield very accurate energy eigenvalues, total energy differences, and wave-function moments over a wide range of excited atomic configurations. We have calculated the potentials for 68 transition and nontransition elements of rows 1--5 in the Periodic Table. Their characteristic features, such as classical turning points and minimum potential radii, faithfully reflect the chemical regularities of the Periodic Table. The nonempirical nature of these potentials permits both an analysis of their dominant features in terms of the underlying interelectronic potentials and the systematic improvement of their predictions through inclusion of appropriate correlation terms. As these potentials accurately reproduce both energy eigenvalues and wave functions and can be readily fit to analytic forms with known asymptotic behavior, they can be used directly for studies of many structural and electronic properties of solids

  8. Forecast of Piezoelectric Properties of Crystalline Materials from First Principles Calculation

    International Nuclear Information System (INIS)

    Zheng Yanqing; Shi Erwei; Chen Jianjun; Zhang Tao; Song Lixin

    2006-01-01

    In this paper, forecast of piezoelectric tensors are presented. Piezo crystals including quartz, quartz-like crystals, known and novel crystals of langasite-type structure are treated with density-functional perturb theory (DFPT) using plane-wave pseudopotentials method, within the local density approximation (LDA) to the exchange-correlation functional. Compared with experimental results, the ab initio calculation results have quantitative or semi-quantitative accuracy. It is shown that first principles calculation opens a door to the search and design of new piezoelectric material. Further application of first principles calculation to forecast the whole piezoelectric properties are also discussed

  9. First-principles density functional calculation of electrochemical stability of fast Li ion conducting garnet-type oxides.

    Science.gov (United States)

    Nakayama, Masanobu; Kotobuki, Masashi; Munakata, Hirokazu; Nogami, Masayuki; Kanamura, Kiyoshi

    2012-07-28

    The research and development of rechargeable all-ceramic lithium batteries are vital to realize their considerable advantages over existing commercial lithium ion batteries in terms of size, energy density, and safety. A key part of such effort is the development of solid-state electrolyte materials with high Li(+) conductivity and good electrochemical stability; lithium-containing oxides with a garnet-type structure are known to satisfy the requirements to achieve both features. Using first-principles density functional theory (DFT), we investigated the electrochemical stability of garnet-type Li(x)La(3)M(2)O(12) (M = Ti, Zr, Nb, Ta, Sb, Bi; x = 5 or 7) materials against Li metal. We found that the electrochemical stability of such materials depends on their composition and structure. The electrochemical stability against Li metal was improved when a cation M was chosen with a low effective nuclear charge, that is, with a high screening constant for an unoccupied orbital. In fact, both our computational and experimental results show that Li(7)La(3)Zr(2)O(12) and Li(5)La(3)Ta(2)O(12) are inert to Li metal. In addition, the linkage of MO(6) octahedra in the crystal structure affects the electrochemical stability. For example, perovskite-type La(1/3)TaO(3) was found, both experimentally and computationally, to react with Li metal owing to the corner-sharing MO(6) octahedral network of La(1/3)TaO(3), even though it has the same constituent elements as garnet-type Li(5)La(3)Ta(2)O(12) (which is inert to Li metal and features isolated TaO(6) octahedra).

  10. First-principles study of complex material systems

    Science.gov (United States)

    He, Lixin

    This thesis covers several topics concerning the study of complex materials systems by first-principles methods. It contains four chapters. A brief, introductory motivation of this work will be given in Chapter 1. In Chapter 2, I will give a short overview of the first-principles methods, including density-functional theory (DFT), planewave pseudopotential methods, and the Berry-phase theory of polarization in crystallines insulators. I then discuss in detail the locality and exponential decay properties of Wannier functions and of related quantities such as the density matrix, and their application in linear-scaling algorithms. In Chapter 3, I investigate the interaction of oxygen vacancies and 180° domain walls in tetragonal PbTiO3 using first-principles methods. Our calculations indicate that the oxygen vacancies have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti--O--Ti bonds, and attempts to model the results with simple continuum models are discussed. CaCu3Ti4O12 (CCTO) has attracted a lot of attention recently because it was found to have an enormous dielectric response over a very wide temperature range. In Chapter 4, I study the electronic and lattice structure, and the lattice dynamical properties, of this system. Our first-principles calculations together with experimental results point towards an extrinsic mechanism as the origin of the unusual dielectric response.

  11. First-principles structures for the close-packed and the 7/2 motif of collagen

    DEFF Research Database (Denmark)

    Jalkanen, Karl J.; Olsen, Kasper; Knapp-Mohammady, Michaela

    2012-01-01

    The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures. The stru......The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures...

  12. Temperature-dependent dielectric function of germanium in the UV–vis spectral range: A first-principles study

    International Nuclear Information System (INIS)

    Yang, J.Y.; Liu, L.H.; Tan, J.Y.

    2014-01-01

    The study of temperature dependence of thermophysical parameter dielectric function is key to understanding thermal radiative transfer in high-temperature environments. Limited by self-radiation and thermal oxidation, however, it is difficult to directly measure the high-temperature dielectric function of solids with present experimental technologies. In this work, we implement two first-principles methods, the ab initio molecular dynamics (AIMD) and density functional perturbation theory (DFPT), to study the temperature dependence of dielectric function of germanium (Ge) in the UV–vis spectral range in order to provide data of high-temperature dielectric function for radiative transfer study in high-temperature environments. Both the two methods successfully predict the temperature dependence of dielectric function of Ge. Moreover, the good agreement between the calculated results of the AIMD approach and experimental data at 825 K enables us to predict the high-temperature dielectric function of Ge with the AIMD method in the UV–vis spectral range. - Highlights: • The temperature dependence of dielectric function of germanium (Ge) is investigated with two first-principles methods. • The temperature effect on dielectric function of Ge is discussed. • The high-temperature dielectric function of Ge is predicted

  13. First-principles prediction of liquid/liquid interfacial tension

    DEFF Research Database (Denmark)

    Andersson, Martin Peter; Bennetzen, M.V.; Klamt, A.

    2014-01-01

    of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid...

  14. First Principles Calculations for X-ray Resonant Spectra and Elastic Properties

    International Nuclear Information System (INIS)

    Yongbin Lee

    2006-01-01

    In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14

  15. Towards Rational Design of Functional Fluoride and Oxyfluoride Materials from First Principles

    Science.gov (United States)

    Charles, Nenian

    Complex transition metal compounds (TMCs) research has produced functional materials with a range of properties, including ferroelectricity, colossal magnetoresistance, nonlinear optical activity and high-temperature superconductivity. Conventional routes to tune properties in transition metal oxides, for example, have relied primarily on cation chemical substitution and interfacial effects in thin film heterostructures. In heteroanionic TMCs, exhibiting two chemically distinct anions coordinating the same or different cations, engineering of the anion sub-lattice for property control is a promising alternative approach. The presence of multiple anions provides additional design variables, such as anion order, that are absent in homoanionic counterparts. The more complex structural and chemical phase space of heteroanionic materials provides a unique opportunity to realize enhanced or unanticipated electronic, optical, and magnetic responses. Although there is growing interest in heteroanionic materials, and synthetic and characterization advances are occurring for these materials, the crystal-chemistry principles for realizing structural and property control are only slowing emerging. This dissertation employs anion engineering to investigate phenomena in transition metal fluorides and oxyfluorides compounds using first principles density functional theory calculations. Oxyfluorides are particularly intriguing owing their tendency to stabilize highly ordered anion sublattices as well as the potential to combine the advantageous properties of transition metal oxides and fluorides. This work 1) addresses the challenges of studying fluorides and oxyfluorides using first principles calculations; 2) evaluates the feasibility of using external stimuli, such as epitaxial strain and hydrostatic pressure, to control properties of fluorides and oxyfluorides; and 3) formulates a computational workflow based on multiple levels of theory and computation to elucidate structure

  16. First-principles photoemission spectroscopy in DNA and RNA nucleobases from Koopmans-compliant functionals

    Science.gov (United States)

    Nguyen, Ngoc Linh; Borghi, Giovanni; Ferretti, Andrea; Marzari, Nicola

    The determination of spectral properties of the DNA and RNA nucleobases from first principles can provide theoretical interpretation for experimental data, but requires complex electronic-structure formulations that fall outside the domain of applicability of common approaches such as density-functional theory. In this work, we show that Koopmans-compliant functionals, constructed to enforce piecewise linearity in energy functionals with respect to fractional occupation-i.e., with respect to charged excitations-can predict not only frontier ionization potentials and electron affinities of the nucleobases with accuracy comparable or superior with that of many-body perturbation theory and high-accuracy quantum chemistry methods, but also the molecular photoemission spectra are shown to be in excellent agreement with experimental ultraviolet photoemsision spectroscopy data. The results highlight the role of Koopmans-compliant functionals as accurate and inexpensive quasiparticle approximations to the spectral potential, which transform DFT into a novel dynamical formalism where electronic properties, and not only total energies, can be correctly accounted for.

  17. Effect of point defects on the electronic density states of SnC nanosheets: First-principles calculations

    Directory of Open Access Journals (Sweden)

    Soleyman Majidi

    Full Text Available In this work, we investigated the electronic and structural properties of various defects including single Sn and C vacancies, double vacancy of the Sn and C atoms, anti-sites, position exchange and the Stone–Wales (SW defects in SnC nanosheets by using density-functional theory (DFT. We found that various vacancy defects in the SnC monolayer can change the electronic and structural properties. Our results show that the SnC is an indirect band gap compound, with the band gap of 2.10 eV. The system turns into metal for both structure of the single Sn and C vacancies. However, for the double vacancy contained Sn and C atoms, the structure remains semiconductor with the direct band gap of 0.37 eV at the G point. We also found that for anti-site defects, the structure remains semiconductor and for the exchange defect, the structure becomes indirect semiconductor with the K-G point and the band gap of 0.74 eV. Finally, the structure of SW defect remains semiconductor with the direct band gap at K point with band gap of 0.54 eV. Keywords: SnC nanosheets, Density-functional theory, First-principles calculations, Electronic density of states, Band gap

  18. Thermal transport across metal silicide-silicon interfaces: First-principles calculations and Green's function transport simulations

    Science.gov (United States)

    Sadasivam, Sridhar; Ye, Ning; Feser, Joseph P.; Charles, James; Miao, Kai; Kubis, Tillmann; Fisher, Timothy S.

    2017-02-01

    Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to the interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi2-Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used "mixing rules" to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that cross-interface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi2-Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with

  19. First-principle optimal local pseudopotentials construction via optimized effective potential method

    International Nuclear Information System (INIS)

    Mi, Wenhui; Zhang, Shoutao; Wang, Yanchao; Ma, Yanming; Miao, Maosheng

    2016-01-01

    The local pseudopotential (LPP) is an important component of orbital-free density functional theory, a promising large-scale simulation method that can maintain information on a material’s electron state. The LPP is usually extracted from solid-state density functional theory calculations, thereby it is difficult to assess its transferability to cases involving very different chemical environments. Here, we reveal a fundamental relation between the first-principles norm-conserving pseudopotential (NCPP) and the LPP. On the basis of this relationship, we demonstrate that the LPP can be constructed optimally from the NCPP for a large number of elements using the optimized effective potential method. Specially, our method provides a unified scheme for constructing and assessing the LPP within the framework of first-principles pseudopotentials. Our practice reveals that the existence of a valid LPP with high transferability may strongly depend on the element.

  20. First-principles density functional theory (DFT) study of gold nanorod and its interaction with alkanethiol ligands.

    Science.gov (United States)

    Hu, Hang; Reven, Linda; Rey, Alejandro

    2013-10-17

    The structure and mechanical properties of gold nanorods and their interactions with alkenthiolate self-assembled monolayers have been determined using a novel first-principle density functional theory simulation approach. The multifaceted, 1-dimensional, octagonal nanorod has alternate Au100 and Au110 surfaces. The structural optimization of the gold nanorods was performed with a mixed basis: the outermost layer of gold atoms used double-ζ plus polarization (DZP), the layer below used double-ζ (DZ), and the inner layers used single-ζ (SZ). The final structure compares favorably with simulations using DZP for all atoms. Phonon dispersion calculations and ab initio molecular dynamics (AIMD) were used to establish the dynamic and thermal stability of the system. From the AIMD simulations it was found that the nanorod system will undergo significant surface reconstruction at 300 K. In addition, when subjected to mechanical stress in the axial direction, the nanorod responds as an orthotropic material, with uniform expansion along the radial direction. The Young's moduli are 207 kbar in the axial direction and 631 kbar in the radial direction. The binding of alkanethiolates, ranging from methanethiol to pentanethiol, caused formation of surface point defects on the Au110 surfaces. On the Au100 surfaces, the defects occurred in the inner layer, creating a small surface island. These defects make positive and negative concavities on the gold nanorod surface, which helps the ligand to achieve a more stable state. The simulation results narrowed significant knowledge gaps on the alkanethiolate adsorption process and on their mutual interactions on gold nanorods. The mechanical characterization offers a new dimension to understand the physical chemistry of these complex nanoparticles.

  1. Corrosion Thermodynamics of Magnesium and Alloys from First Principles as a Function of Solvation

    Science.gov (United States)

    Limmer, Krista; Williams, Kristen; Andzelm, Jan

    Thermodynamics of corrosion processes occurring on magnesium surfaces, such as hydrogen evolution and water dissociation, have been examined with density functional theory (DFT) to evaluate the effect of impurities and dilute alloying additions. The modeling of corrosion thermodynamics requires examination of species in a variety of chemical and electronic states in order to accurately represent the complex electrochemical corrosion process. In this study, DFT calculations for magnesium corrosion thermodynamics were performed with two DFT codes (VASP and DMol3), with multiple exchange-correlation functionals for chemical accuracy, as well as with various levels of implicit and explicit solvation for surfaces and solvated ions. The accuracy of the first principles calculations has been validated against Pourbaix diagrams constructed from solid, gas and solvated charged ion calculations. For aqueous corrosion, it is shown that a well parameterized implicit solvent is capable of accurately representing all but the first coordinating layer of explicit water for charged ions.

  2. Maximum Principles and Boundary Value Problems for First-Order Neutral Functional Differential Equations

    Directory of Open Access Journals (Sweden)

    Domoshnitsky Alexander

    2009-01-01

    Full Text Available We obtain the maximum principles for the first-order neutral functional differential equation where , and are linear continuous operators, and are positive operators, is the space of continuous functions, and is the space of essentially bounded functions defined on . New tests on positivity of the Cauchy function and its derivative are proposed. Results on existence and uniqueness of solutions for various boundary value problems are obtained on the basis of the maximum principles.

  3. First principles study of electronic, elastic and thermal properties of lutetium intermetallics

    International Nuclear Information System (INIS)

    Pagare, Gitanjali; Chouhan, Sunil Singh; Soni, Pooja; Sanyal, S.P.; Rajagopalan, M.

    2011-01-01

    In the present work, the electronic, elastic and thermal properties of lutetium intermetallics LuX have been studied theoretically by using first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GCA)

  4. Engineering the work function of armchair graphene nanoribbons using strain and functional species: a first principles study

    International Nuclear Information System (INIS)

    Peng Xihong; Tang Fu; Copple, Andrew

    2012-01-01

    First principles density functional theory calculations were performed to study the effects of strain, edge passivation, and surface functional species on the structural and electronic properties of armchair graphene nanoribbons (AGNRs), with a particular focus on the work function. The work function was found to increase with uniaxial tensile strain and decrease with compression. The variation of the work function under strain is primarily due to the shift of the Fermi energy with strain. In addition, the relationship between the work function variation and the core level shift with strain is discussed. Distinct trends of the core level shift under tensile and compressive strain were discovered. For AGNRs with the edge carbon atoms passivated by oxygen, the work function is higher than for nanoribbons with the edge passivated by hydrogen under a moderate strain. The difference between the work functions in these two edge passivations is enlarged (reduced) under a sufficient tensile (compressive) strain. This has been correlated to a direct-indirect bandgap transition for tensile strains of about 4% and to a structural transformation for large compressive strains at about - 12%. Furthermore, the effect of the surface species decoration, such as H, F, or OH with different covering density, was investigated. It was found that the work function varies with the type and coverage of surface functional species. Decoration with F and OH increases the work function while H decreases it. The surface functional species were decorated on either one side or both sides of AGNRs. The difference in the work functions between one-sided and two-sided decorations was found to be relatively small, which may suggest an introduced surface dipole plays a minor role. (paper)

  5. First principles calculation of two dimensional antimony and antimony arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Pillai, Sharad Babu, E-mail: sbpillai001@gmail.com; Narayan, Som; Jha, Prafulla K. [Department. of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara-390002 (India); Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364001 (India)

    2016-05-23

    This work focuses on the strain dependence of the electronic properties of two dimensional antimony (Sb) material and its alloy with As (SbAs) using density functional theory based first principles calculations. Both systems show indirect bandgap semiconducting character which can be transformed into a direct bandgap material with the application of relatively small strain.

  6. Boron Fullerenes: A First-Principles Study

    Directory of Open Access Journals (Sweden)

    Gonzalez Szwacki Nevill

    2007-01-01

    Full Text Available AbstractA family of unusually stable boron cages was identified and examined using first-principles local-density functional method. The structure of the fullerenes is similar to that of the B12icosahedron and consists of six crossing double-rings. The energetically most stable fullerene is made up of 180 boron atoms. A connection between the fullerene family and its precursors, boron sheets, is made. We show that the most stable boron sheets are not necessarily precursors of very stable boron cages. Our finding is a step forward in the understanding of the structure of the recently produced boron nanotubes.

  7. First-principles simulations of heat transport

    Science.gov (United States)

    Puligheddu, Marcello; Gygi, Francois; Galli, Giulia

    2017-11-01

    Advances in understanding heat transport in solids were recently reported by both experiment and theory. However an efficient and predictive quantum simulation framework to investigate thermal properties of solids, with the same complexity as classical simulations, has not yet been developed. Here we present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at close to equilibrium conditions, which only requires calculations of first-principles trajectories and atomic forces, thus avoiding direct computation of heat currents and energy densities. In addition the method requires much shorter sequential simulation times than ordinary molecular dynamics techniques, making it applicable within density functional theory. We discuss results for a representative oxide, MgO, at different temperatures and for ordered and nanostructured morphologies, showing the performance of the method in different conditions.

  8. First principles study of α and δ-Pu

    International Nuclear Information System (INIS)

    Chattaraj, Debabrata; Dash, Smruti

    2017-01-01

    The structural and electronic properties of α-and δ-Pu has been investigated using state of the art first principles method. All the calculations have been performed using a plane wave based pseudopotential method under the framework of spin polarized density functional theory. The effect of relativistic spin-orbit interactions on these properties has been investigated. The calculated lattice parameters are found to be within ±1% of the experimental data. The cohesive energy of α-and δ-Pu are calculated to be -3.125 and -3.126 eV/atom. The nature of chemical bonding present in those phases of Pu is depicted by calculated density of states spectra. (author)

  9. First-principles X-ray absorption dose calculation for time-dependent mass and optical density.

    Science.gov (United States)

    Berejnov, Viatcheslav; Rubinstein, Boris; Melo, Lis G A; Hitchcock, Adam P

    2018-05-01

    A dose integral of time-dependent X-ray absorption under conditions of variable photon energy and changing sample mass is derived from first principles starting with the Beer-Lambert (BL) absorption model. For a given photon energy the BL dose integral D(e, t) reduces to the product of an effective time integral T(t) and a dose rate R(e). Two approximations of the time-dependent optical density, i.e. exponential A(t) = c + aexp(-bt) for first-order kinetics and hyperbolic A(t) = c + a/(b + t) for second-order kinetics, were considered for BL dose evaluation. For both models three methods of evaluating the effective time integral are considered: analytical integration, approximation by a function, and calculation of the asymptotic behaviour at large times. Data for poly(methyl methacrylate) and perfluorosulfonic acid polymers measured by scanning transmission soft X-ray microscopy were used to test the BL dose calculation. It was found that a previous method to calculate time-dependent dose underestimates the dose in mass loss situations, depending on the applied exposure time. All these methods here show that the BL dose is proportional to the exposure time D(e, t) ≃ K(e)t.

  10. Hierarchical Coupling of First-Principles Molecular Dynamics with Advanced Sampling Methods.

    Science.gov (United States)

    Sevgen, Emre; Giberti, Federico; Sidky, Hythem; Whitmer, Jonathan K; Galli, Giulia; Gygi, Francois; de Pablo, Juan J

    2018-05-14

    We present a seamless coupling of a suite of codes designed to perform advanced sampling simulations, with a first-principles molecular dynamics (MD) engine. As an illustrative example, we discuss results for the free energy and potential surfaces of the alanine dipeptide obtained using both local and hybrid density functionals (DFT), and we compare them with those of a widely used classical force field, Amber99sb. In our calculations, the efficiency of first-principles MD using hybrid functionals is augmented by hierarchical sampling, where hybrid free energy calculations are initiated using estimates obtained with local functionals. We find that the free energy surfaces obtained from classical and first-principles calculations differ. Compared to DFT results, the classical force field overestimates the internal energy contribution of high free energy states, and it underestimates the entropic contribution along the entire free energy profile. Using the string method, we illustrate how these differences lead to different transition pathways connecting the metastable minima of the alanine dipeptide. In larger peptides, those differences would lead to qualitatively different results for the equilibrium structure and conformation of these molecules.

  11. First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys

    KAUST Repository

    Noor, Naveed Ahmed; Ikram, Nazma; Ali, Sana Zulfiqar; Nazir, Safdar; Alay-E-Abbas, Syed Muhammad; Shaukat, Ali

    2010-01-01

    Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS

  12. Quantal density functional theory

    CERN Document Server

    Sahni, Viraht

    2016-01-01

    This book deals with quantal density functional theory (QDFT) which is a time-dependent local effective potential theory of the electronic structure of matter. The treated time-independent QDFT constitutes a special case. In the 2nd edition, the theory is extended to include the presence of external magnetostatic fields. The theory is a description of matter based on the ‘quantal Newtonian’ first and second laws which is in terms of “classical” fields that pervade all space, and their quantal sources. The fields, which are explicitly defined, are separately representative of electron correlations due to the Pauli exclusion principle, Coulomb repulsion, correlation-kinetic, correlation-current-density, and correlation-magnetic effects. The book further describes Schrödinger theory from the new physical perspective of fields and quantal sources. It also describes traditional Hohenberg-Kohn-Sham DFT, and explains via QDFT the physics underlying the various energy functionals and functional derivatives o...

  13. Adsorption of organic molecules on mineral surfaces studied by first-principle calculations: A review.

    Science.gov (United States)

    Zhao, Hongxia; Yang, Yong; Shu, Xin; Wang, Yanwei; Ran, Qianping

    2018-04-09

    First-principle calculations, especially by the density functional theory (DFT) methods, are becoming a power technique to study molecular structure and properties of organic/inorganic interfaces. This review introduces some recent examples on the study of adsorption models of organic molecules or oligomers on mineral surfaces and interfacial properties obtained from first-principles calculations. The aim of this contribution is to inspire scientists to benefit from first-principle calculations and to apply the similar strategies when studying and tailoring interfacial properties at the atomistic scale, especially for those interested in the design and development of new molecules and new products. Copyright © 2017. Published by Elsevier B.V.

  14. New approaches for first-principles modelling of inelastic transport in nanoscale semiconductor devices with thousands of atoms

    DEFF Research Database (Denmark)

    Gunst, Tue; Brandbyge, Mads; Palsgaard, Mattias Lau Nøhr

    2017-01-01

    is in both methods calculated in a post-processing step to a self consistent DFT calculation. The first method is based on first order perturbation theory in the EPC self-energy within the Lowest Order Expansion (LOE) approximation. The method requires calculation of the first-principles EPC in the device......We present two different methods which both enable large-scale first-principles device simulations including electron-phonon coupling (EPC). The methods are based on Density Functional Theory and Nonequilibrium Greens Functions (DFT- NEGF) calculations of electron transport. The inelastic current...

  15. JDFTx: Software for joint density-functional theory

    Directory of Open Access Journals (Sweden)

    Ravishankar Sundararaman

    2017-01-01

    Full Text Available Density-functional theory (DFT has revolutionized computational prediction of atomic-scale properties from first principles in physics, chemistry and materials science. Continuing development of new methods is necessary for accurate predictions of new classes of materials and properties, and for connecting to nano- and mesoscale properties using coarse-grained theories. JDFTx is a fully-featured open-source electronic DFT software designed specifically to facilitate rapid development of new theories, models and algorithms. Using an algebraic formulation as an abstraction layer, compact C++11 code automatically performs well on diverse hardware including GPUs (Graphics Processing Units. This code hosts the development of joint density-functional theory (JDFT that combines electronic DFT with classical DFT and continuum models of liquids for first-principles calculations of solvated and electrochemical systems. In addition, the modular nature of the code makes it easy to extend and interface with, facilitating the development of multi-scale toolkits that connect to ab initio calculations, e.g. photo-excited carrier dynamics combining electron and phonon calculations with electromagnetic simulations.

  16. First-principles analysis of the Raman spectrum of vitreous silica: comparison with the vibrational density of states

    International Nuclear Information System (INIS)

    Umari, P; Pasquarello, Alfredo

    2003-01-01

    The HH and HV Raman spectra of vitreous silica are calculated from first principles for a model structure consisting of a disordered network of corner-sharing tetrahedra, for which the vibrational properties were obtained previously. We analyse the contribution of specific atomic motions to the Raman spectra and perform a detailed comparison with respect to the vibrational density of states. We find that the HV spectrum closely resembles the vibrational density of states. By comparison, the HH spectrum shows significant differences and arises almost exclusively from oxygen vibrations

  17. First-principles analysis of the Raman spectrum of vitreous silica: comparison with the vibrational density of states

    Energy Technology Data Exchange (ETDEWEB)

    Umari, P; Pasquarello, Alfredo [Institut de Theorie des Phenomenes Physiques (ITP), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Institut Romand de Recherche Numerique en Physique des Materiaux (IRRMA), CH-1015 Lausanne (Switzerland)

    2003-04-30

    The HH and HV Raman spectra of vitreous silica are calculated from first principles for a model structure consisting of a disordered network of corner-sharing tetrahedra, for which the vibrational properties were obtained previously. We analyse the contribution of specific atomic motions to the Raman spectra and perform a detailed comparison with respect to the vibrational density of states. We find that the HV spectrum closely resembles the vibrational density of states. By comparison, the HH spectrum shows significant differences and arises almost exclusively from oxygen vibrations.

  18. First-principles study of the interaction and charge transfer between graphene and metals

    NARCIS (Netherlands)

    Khomyakov, Petr; Giovannetti, G.; Rusu, P.C.; Brocks, G.; van den Brink, J.; Kelly, Paul J.

    2009-01-01

    Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density-functional theory. The bonding of graphene to Al, Ag, Cu, Au,

  19. Assessment of Density-Functional Tight-Binding Ionization Potentials and Electron Affinities of Molecules of Interest for Organic Solar Cells Against First-Principles GW Calculations

    Directory of Open Access Journals (Sweden)

    Ala Aldin M. H. M. Darghouth

    2015-12-01

    Full Text Available Ionization potentials (IPs and electron affinities (EAs are important quantities input into most models for calculating the open-circuit voltage (Voc of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB method with the third-order self-consistent charge (SCC correction and the 3ob parameter set (the third-order DFTB (DFTB3 organic and biochemistry parameter set against experiments (for smaller molecules and against first-principles GW (Green’s function, G, times the screened potential, W calculations (for larger molecules of interest in organic electronics for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT, but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field SCC-DFTB calculations for first IPs (good to ± 0.649 eV. When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT IPs as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of

  20. First-principles elasticity of monocarboaluminate hydrates

    KAUST Repository

    Moon, J.; Yoon, S.; Wentzcovitch, R. M.; Monteiro, P. J. M.

    2014-01-01

    The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.

  1. First-principles elasticity of monocarboaluminate hydrates

    KAUST Repository

    Moon, J.

    2014-07-01

    The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.

  2. First-principles study of structural and work function properties for nitrogen-doped single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Shao, Xiji; Li, Detian; Cai, Jianqiu; Luo, Haijun; Dong, Changkun

    2016-01-01

    Graphical abstract: - Highlights: • Substitutional nitrogen atom doping in capped (5, 5) SWNT is investigated. • Serious defects appear from breaks of C−N bonds with N contents of above 23.3 at.%. • Work function drops after N doping and may reach 4.1 eV. - Abstract: The structural and electronic properties of the capped (5, 5) single-walled carbon nanotube (SWNT), including the structural stability, the work function, and the charge transfer performance, are investigated for the substitutional nitrogen atom doping under different concentrations by first-principles density functional theory. The geometrical structure keeps almost intact with single or two N atom doping, while C−N bonds may break up with serious defects for N concentrations of 23.3 at.% and above. The SWNT remains metallic and the work function drops after doping due to the upward shift of Fermi level, leading to the increase of the electrical conductivity. N doping enhances the oxygen reduction activity stronger than N adsorption because of higher charge transfers.

  3. First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron

    Science.gov (United States)

    Kakehashi, Yoshiro; Chandra, Sumal

    2016-04-01

    We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the d electrons with eg symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.

  4. Proof-of-principle functionals for the shape function

    International Nuclear Information System (INIS)

    Ayers, Paul W.

    2005-01-01

    Recently, it has been shown that the density per particle, or shape function, determines all the properties of molecules and, more generally, finite Coulomb systems (e.g., clusters). Here, we provide numerical evidence for this 'existence' theorem, showing that atomic properties (specifically the kinetic energy and exchange energy) have simple approximate expressions in terms of the shape function. While the accuracy of our results is limited, this provides 'proof-of-principle' evidence that shape-functional theory represents an alternative to density-functional theory for finite Coulomb systems

  5. Origin of current-induced forces in an atomic gold wire: A first-principles study

    DEFF Research Database (Denmark)

    Brandbyge, Mads; Stokbro, Kurt; Taylor, Jeremy Philip

    2003-01-01

    We address the microscopic origin of the current-induced forces by analyzing results of first principles density functional calculations of atomic gold wires connected to two gold electrodes with different electrochemical potentials. We find that current induced forces are closely related...

  6. Exact results and open questions in first principle functional RG

    International Nuclear Information System (INIS)

    Le Doussal, Pierre

    2010-01-01

    Some aspects of the functional RG (FRG) approach to pinned elastic manifolds (of internal dimension d) at finite temperature T > 0 are reviewed and reexamined in this much expanded version of Le Doussal (2006) . The particle limit d = 0 provides a test for the theory: there the FRG is equivalent to the decaying Burgers equation, with viscosity ν ∼ T-both being formally irrelevant. An outstanding question in FRG, i.e. how temperature regularizes the otherwise singular flow of T = 0 FRG, maps to the viscous layer regularization of inertial range Burgers turbulence (i.e. to the construction of the inviscid limit). Analogy between Kolmogorov scaling and FRG cumulant scaling is discussed. First, multi-loop FRG corrections are examined and the direct loop expansion at T > 0 is shown to fail already in d = 0, a hierarchy of ERG equations being then required (introduced in Balents and Le Doussal (2005) ). Next we prove that the FRG function R(u) and higher cumulants defined from the field theory can be obtained for any d from moments of a renormalized potential defined in an sliding harmonic well. This allows to measure the fixed point function R(u) in numerics and experiments. In d = 0 the beta function (of the inviscid limit) is obtained from first principles to four loop. For Sinai model (uncorrelated Burgers initial velocities) the ERG hierarchy can be solved and the exact function R(u) is obtained. Connections to exact solutions for the statistics of shocks in Burgers and to ballistic aggregation are detailed. A relation is established between the size distribution of shocks and the one for droplets. A droplet solution to the ERG functional hierarchy is found for any d, and the form of R(u) in the thermal boundary layer is related to droplet probabilities. These being known for the d = 0 Sinai model the function R(u) is obtained there at any T. Consistency of the ε=4-d expansion in one and two loop FRG is studied from first principles, and connected to shock and

  7. Anomalous doping effect in black phosphorene from first-principles calculations

    OpenAIRE

    Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2014-01-01

    Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with odd...

  8. A first principle study of band structure of III-nitride compounds

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

    2005-12-15

    The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

  9. First-principles momentum-dependent local ansatz wavefunction and momentum distribution function bands of iron

    International Nuclear Information System (INIS)

    Kakehashi, Yoshiro; Chandra, Sumal

    2016-01-01

    We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi–Dirac function for the d electrons with e g symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data. (author)

  10. Glass polymorphism in amorphous germanium probed by first-principles computer simulations

    Science.gov (United States)

    Mancini, G.; Celino, M.; Iesari, F.; Di Cicco, A.

    2016-01-01

    The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions.

  11. Open-system Kohn-Sham density functional theory.

    Science.gov (United States)

    Zhou, Yongxi; Ernzerhof, Matthias

    2012-03-07

    A simple model for electron transport through molecules is provided by the source-sink potential (SSP) method [F. Goyer, M. Ernzerhof, and M. Zhuang, J. Chem. Phys. 126, 144104 (2007)]. In SSP, the boundary conditions of having an incoming and outgoing electron current are enforced through complex potentials that are added to the Hamiltonian. Depending on the sign of the imaginary part of the potentials, current density is generated or absorbed. In this way, a finite system can be used to model infinite molecular electronic devices. The SSP has originally been developed for the Hückel method and subsequently it has been extended [F. Goyer and M. Ernzerhof, J. Chem. Phys. 134, 174101 (2011)] to the Hubbard model. Here we present a step towards its generalization for first-principles electronic structure theory methods. In particular, drawing on our earlier work, we discuss a new generalized density functional theory for complex non-Hermitian Hamiltonians. This theory enables us to combine SSP and Kohn-Sham theory to obtain a method for the description of open systems that exchange current density with their environment. Similarly, the Hartree-Fock method is extended to the realm of non-Hermitian, SSP containing Hamiltonians. As a proof of principle, we present the first applications of complex-density functional theory (CODFT) as well as non-Hermitian Hartree-Fock theory to electron transport through molecules. © 2012 American Institute of Physics

  12. Generalization of first-principles thermodynamic model: Application to hexagonal close-packed ε-Fe3N

    DEFF Research Database (Denmark)

    Bakkedal, Morten B.; Shang, Shu- Li; Liu, Zi-Kui

    2016-01-01

    A complete first-principles thermodynamic model was developed and applied to hexagonal close-packed structure ε-Fe3N. The electronic structure was calculated using density functional theory and the quasiharmonic phonon approximation to determine macroscopic thermodynamic properties at finite...

  13. First-principles equation-of-state table of silicon and its effects on high-energy-density plasma simulations

    Science.gov (United States)

    Hu, S. X.; Gao, R.; Ding, Y.; Collins, L. A.; Kress, J. D.

    2017-04-01

    Using density-functional theory-based molecular-dynamics simulations, we have investigated the equation of state for silicon in a wide range of plasma density and temperature conditions of ρ =0.001 -500 g /c m3 and T =2000 -108K . With these calculations, we have established a first-principles equation-of-state (FPEOS) table of silicon for high-energy-density (HED) plasma simulations. When compared with the widely used SESAME-EOS model (Table 3810), we find that the FPEOS-predicted Hugoniot is ˜20% softer; for off-Hugoniot plasma conditions, the pressure and internal energy in FPEOS are lower than those of SESAME EOS for temperatures above T ≈ 1-10 eV (depending on density), while the former becomes higher in the low-T regime. The pressure difference between FPEOS and SESAME 3810 can reach to ˜50%, especially in the warm-dense-matter regime. Implementing the FPEOS table of silicon into our hydrocodes, we have studied its effects on Si-target implosions. When compared with the one-dimensional radiation-hydrodynamics simulation using the SESAME 3810 EOS model, the FPEOS simulation showed that (1) the shock speed in silicon is ˜10% slower; (2) the peak density of an in-flight Si shell during implosion is ˜20% higher than the SESAME 3810 simulation; (3) the maximum density reached in the FPEOS simulation is ˜40% higher at the peak compression; and (4) the final areal density and neutron yield are, respectively, ˜30% and ˜70% higher predicted by FPEOS versus the traditional simulation using SESAME 3810. All of these features can be attributed to the larger compressibility of silicon predicted by FPEOS. These results indicate that an accurate EOS table, like the FPEOS presented here, could be essential for the precise design of targets for HED experiments.

  14. Structural, electronic, and vibrational properties of high-density amorphous silicon: a first-principles molecular-dynamics study.

    Science.gov (United States)

    Morishita, Tetsuya

    2009-05-21

    We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).

  15. First-principles calculation of the magnetic properties of paramagnetic fcc iron

    International Nuclear Information System (INIS)

    Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.

    1985-01-01

    Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments

  16. First principles molecular dynamics of metal/water interfaces under bias potential

    Science.gov (United States)

    Pedroza, Luana; Brandimarte, Pedro; Rocha, Alexandre; Fernandez-Serra, Marivi

    2014-03-01

    Understanding the interaction of the water-metal system at an atomic level is extremely important in electrocatalysts for fuel cells, photocatalysis among other systems. The question of the interface energetics involves a detailed study of the nature of the interactions between water-water and water-substrate. A first principles description of all components of the system is the most appropriate methodology in order to advance understanding of electrochemically processes. In this work we describe, using first principles molecular dynamics simulations, the dynamics of a combined surface(Au and Pd)/water system both in the presence and absence of an external bias potential applied to the electrodes, as one would come across in electrochemistry. This is accomplished using a combination of density functional theory (DFT) and non-equilibrium Green's functions methods (NEGF), thus accounting for the fact that one is dealing with an out-of-equilibrium open system, with and without van der Waals interactions. DOE Early Career Award No. DE-SC0003871.

  17. Surface structure and properties of functionalized nanodiamonds: a first-principles study

    International Nuclear Information System (INIS)

    Datta, Aditi; Kirca, Mesut; Fu Yao; To, Albert C

    2011-01-01

    The goal of this work is to gain fundamental understanding of the surface and internal structure of functionalized detonation nanodiamonds (NDs) using quantum mechanics based density functional theory (DFT) calculations. The unique structure of ND assists in the binding of different functional groups to its surface which in turn facilitates binding with drug molecules. The ability to comprehensively model the surface properties, as well as drug-ND interactions during functionalization, is a challenge and is the problem of our interest. First, the structure of NDs of technologically relevant size (∼5 nm) was optimized using classical mechanics based molecular mechanics simulations. Quantum mechanics based density functional theory (DFT) was then employed to analyse the properties of smaller relevant parts of the optimized cluster further to address the effect of functionalization on the stability of the cluster and reactivity at its surface. It is found that functionalization is preferred over reconstruction at the (100) surface and promotes graphitization in the (111) surface for NDs functionalized with the carbonyl oxygen (C = O) group. It is also seen that the edges of ND are the preferred sites for functionalization with the carboxyl group (-COOH) vis-a-vis the corners of ND.

  18. Surface structure and properties of functionalized nanodiamonds: a first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Datta, Aditi; Kirca, Mesut; Fu Yao; To, Albert C, E-mail: albertto@pitt.edu [Department of Mechanical Engineering and Materials Science and Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States)

    2011-02-11

    The goal of this work is to gain fundamental understanding of the surface and internal structure of functionalized detonation nanodiamonds (NDs) using quantum mechanics based density functional theory (DFT) calculations. The unique structure of ND assists in the binding of different functional groups to its surface which in turn facilitates binding with drug molecules. The ability to comprehensively model the surface properties, as well as drug-ND interactions during functionalization, is a challenge and is the problem of our interest. First, the structure of NDs of technologically relevant size ({approx}5 nm) was optimized using classical mechanics based molecular mechanics simulations. Quantum mechanics based density functional theory (DFT) was then employed to analyse the properties of smaller relevant parts of the optimized cluster further to address the effect of functionalization on the stability of the cluster and reactivity at its surface. It is found that functionalization is preferred over reconstruction at the (100) surface and promotes graphitization in the (111) surface for NDs functionalized with the carbonyl oxygen (C = O) group. It is also seen that the edges of ND are the preferred sites for functionalization with the carboxyl group (-COOH) vis-a-vis the corners of ND.

  19. First-principles study on the creation of holes in high Tc cuprates

    International Nuclear Information System (INIS)

    Ambrosch-Draxl, C.; Sherman, E.Ya.; Auer, H.; Thonhauser, T.

    2004-01-01

    We investigate the charge redistribution in high T c cuprates as a function of pressure, composition, and doping. To this extent we have performed first-principles calculations based on density functional theory for several representatives of the Hg based cuprates. In particular, we focus on the creation of holes in the copper-oxygen planes. Conclusions are drawn about the similarities and differences between the three parameters influencing the superconducting transition temperature. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Isobaric-isothermal Monte Carlo simulations from first principles: Application to liquid water at ambient conditions

    Energy Technology Data Exchange (ETDEWEB)

    McGrath, M; Siepmann, J I; Kuo, I W; Mundy, C J; VandeVondele, J; Hutter, J; Mohamed, F; Krack, M

    2004-12-02

    A series of first principles Monte Carlo simulations in the isobaric-isothermal ensemble were carried out for liquid water at ambient conditions (T = 298 K and p = 1 atm). The Becke-Lee-Yang-Parr (BLYP) exchange and correlation energy functionals and norm-conserving Goedecker-Teter-Hutter (GTH) pseudopotentials were employed with the CP2K simulation package to examine systems consisting of 64 water molecules. The fluctuations in the system volume encountered in simulations in the isobaric-isothermal ensemble requires a reconsideration of the suitability of the typical charge density cutoff and the regular grid generation method previously used for the computation of the electrostatic energy in first principles simulations in the microcanonical or canonical ensembles. In particular, it is noted that a much higher cutoff is needed and that the most computationally efficient method of creating grids can result in poor simulations. Analysis of the simulation trajectories using a very large charge density cutoff at 1200 Ry and four different grid generation methods point to a substantially underestimated liquid density of about 0.85 g/cm{sup 3} resulting in a somewhat understructured liquid (with a value of about 2.7 for the height of the first peak in the oxygen/oxygen radial distribution function) for BLYP-GTH water at ambient conditions.

  1. Band gap of β-PtO2 from first-principles

    Directory of Open Access Journals (Sweden)

    Yong Yang

    2012-06-01

    Full Text Available We studied the band gap of β-PtO2 using first-principles calculations based on density functional theory (DFT. The results are obtained within the framework of the generalized gradient approximation (GGA, GGA+U, GW, and the hybrid functional methods. For the different types of calculations, the calculated band gap increases from ∼0.46 eV to 1.80 eV. In particular, the band gap by GW (conventional and self-consistent calculation shows a tendency of converging to ∼1.25 ± 0.05 eV. The effect of on-site Coulomb interaction on the bonding characteristics is also analyzed.

  2. Thermodynamic properties of Mg2Si and Mg2Ge investigated by first principles method

    International Nuclear Information System (INIS)

    Wang, Hanfu; Jin, Hao; Chu, Weiguo; Guo, Yanjun

    2010-01-01

    The lattice dynamics and thermodynamic properties of Mg 2 Si and Mg 2 Ge are studied based on the first principles calculations. We obtain the phonon dispersion curves and phonon density of states spectra using the density functional perturbation theory with local density approximations. By employing the quasi-harmonic approximation, we calculate the temperature dependent Helmholtz free energy, bulk modulus, thermal expansion coefficient, specific heat, Debye temperature and overall Grueneisen coefficient. The results are in good agreement with available experimental data and previous theoretical studies. The thermal conductivities of both compounds are then estimated with the Slack's equation. By carefully choosing input parameters, especially the acoustic Debye temperature, we find that the calculated thermal conductivities agree fairly well with the experimental values above 80 K for both compounds. This demonstrates that the lattice thermal conductivity of simple cubic semiconductors may be estimated with satisfactory accuracy by combining the Slack's equation with the necessary thermodynamics parameters derived completely from the first principles calculations.

  3. Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials

    International Nuclear Information System (INIS)

    Klepeis, J E

    2005-01-01

    The purpose of this paper is to provide an introduction for non-experts to first-principles electronic structure methods that are widely used in the field of condensed-matter physics, including applications to actinide materials. The methods I describe are based on density functional theory (DFT) within the local density approximation (LDA) and the generalized gradient approximation (GGA). In addition to explaining the meaning of this terminology I also describe the underlying theory itself in some detail in order to enable a better understanding of the relative strengths and weaknesses of the methods. I briefly mention some particular numerical implementations of DFT, including the linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods, as well as general methodologies that go beyond DFT and specifically address some of the weaknesses of the theory. The last third of the paper is devoted to a few selected applications that illustrate the ideas discussed in the first two-thirds. In particular, I conclude by addressing the current controversy regarding magnetic DFT calculations for actinide materials. Throughout this paper particular emphasis is placed on providing the appropriate background to enable the non-expert to gain a better appreciation of the application of first-principles electronic structure methods to the study of actinide and other materials

  4. First-Principles Vibrational Electron Energy Loss Spectroscopy of β -Guanine

    Science.gov (United States)

    Radtke, G.; Taverna, D.; Lazzeri, M.; Balan, E.

    2017-07-01

    A general approach to model vibrational electron energy loss spectra obtained using an electron beam positioned away from the specimen is presented. The energy-loss probability of the fast electron is evaluated using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The validity of the method is assessed using recently measured anhydrous β -guanine, an important molecular solid used by animals to produce structural colors. The good agreement between theory and experiments lays the basis for a quantitative interpretation of this spectroscopy in complex systems.

  5. First principle study of structural, electronic and fermi surface properties of aluminum praseodymium

    Science.gov (United States)

    Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.

    2018-05-01

    We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.

  6. First-principles study of the diffusion mechanisms of the self-interstitial in germanium

    International Nuclear Information System (INIS)

    Carvalho, A; Jones, R; Janke, C; Goss, J P; Briddon, P R; Oeberg, S

    2008-01-01

    The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed

  7. Point defects in thorium nitride: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina)

    2016-11-15

    Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

  8. Point defects in thorium nitride: A first-principles study

    International Nuclear Information System (INIS)

    Pérez Daroca, D.; Llois, A.M.; Mosca, H.O.

    2016-01-01

    Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

  9. First-principles studies of PETN molecular crystal vibrational frequencies under high pressure

    Science.gov (United States)

    Perger, Warren; Zhao, Jijun

    2005-07-01

    The vibrational frequencies of the PETN molecular crystal were calculated using the first-principles CRYSTAL03 program which employs an all-electron LCAO approach and calculates analytic first derivatives of the total energy with respect to atomic displacements. Numerical second derivatives were used to enable calculation of the vibrational frequencies at ambient pressure and under various states of compression. Three different density functionals, B3LYP, PW91, and X3LYP were used to examine the effect of the exchange-correlation functional on the vibrational frequencies. The pressure-induced shift of the vibrational frequencies will be presented and compared with experiment. The average deviation with experimental results is shown to be on the order of 2-3%, depending on the functional used.

  10. Accurate first-principles structures and energies of diversely bonded systems from an efficient density functional.

    Science.gov (United States)

    Sun, Jianwei; Remsing, Richard C; Zhang, Yubo; Sun, Zhaoru; Ruzsinszky, Adrienn; Peng, Haowei; Yang, Zenghui; Paul, Arpita; Waghmare, Umesh; Wu, Xifan; Klein, Michael L; Perdew, John P

    2016-09-01

    One atom or molecule binds to another through various types of bond, the strengths of which range from several meV to several eV. Although some computational methods can provide accurate descriptions of all bond types, those methods are not efficient enough for many studies (for example, large systems, ab initio molecular dynamics and high-throughput searches for functional materials). Here, we show that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) within the density functional theory framework predicts accurate geometries and energies of diversely bonded molecules and materials (including covalent, metallic, ionic, hydrogen and van der Waals bonds). This represents a significant improvement at comparable efficiency over its predecessors, the GGAs that currently dominate materials computation. Often, SCAN matches or improves on the accuracy of a computationally expensive hybrid functional, at almost-GGA cost. SCAN is therefore expected to have a broad impact on chemistry and materials science.

  11. Thermodynamic and redox properties of graphene oxides for lithium-ion battery applications: a first principles density functional theory modeling approach.

    Science.gov (United States)

    Kim, Sunghee; Kim, Ki Chul; Lee, Seung Woo; Jang, Seung Soon

    2016-07-27

    Understanding the thermodynamic stability and redox properties of oxygen functional groups on graphene is critical to systematically design stable graphene-based positive electrode materials with high potential for lithium-ion battery applications. In this work, we study the thermodynamic and redox properties of graphene functionalized with carbonyl and hydroxyl groups, and the evolution of these properties with the number, types and distribution of functional groups by employing the density functional theory method. It is found that the redox potential of the functionalized graphene is sensitive to the types, number, and distribution of oxygen functional groups. First, the carbonyl group induces higher redox potential than the hydroxyl group. Second, more carbonyl groups would result in higher redox potential. Lastly, the locally concentrated distribution of the carbonyl group is more beneficial to have higher redox potential compared to the uniformly dispersed distribution. In contrast, the distribution of the hydroxyl group does not affect the redox potential significantly. Thermodynamic investigation demonstrates that the incorporation of carbonyl groups at the edge of graphene is a promising strategy for designing thermodynamically stable positive electrode materials with high redox potentials.

  12. Elastic properties of cubic perovskite BaRuO{sub 3} from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Han Deming; Liu Xiaojuan; Lv Shuhui; Li Hongping [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian, E-mail: jmeng@ciac.jl.c [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

    2010-08-01

    We present first-principles investigations on the structural and elastic properties of the cubic perovskite BaRuO{sub 3} using density-functional theory within both local density approximation (LDA) and generalized gradient approximation (GGA). Basic physical properties, such as lattice constant, shear modulus, elastic constants (C{sub ij}) are calculated. The calculated energy band structures show that the cubic perovskite BaRuO{sub 3} is metallic. We have also predicted the Young's modulus (Y), Poisson's ratio ({upsilon}), and Anisotropy factor (A).

  13. First-principles investigation of mechanical properties of silicene, germanene and stanene

    Science.gov (United States)

    Mortazavi, Bohayra; Rahaman, Obaidur; Makaremi, Meysam; Dianat, Arezoo; Cuniberti, Gianaurelio; Rabczuk, Timon

    2017-03-01

    Two-dimensional allotropes of group-IV substrates including silicene, germanene and stanene have recently attracted considerable attention in nanodevice fabrication industry. These materials involving the buckled structure have been experimentally fabricated lately. In this study, first-principles density functional theory calculations were utilized to investigate the mechanical properties of single-layer and free-standing silicene, germanene and stanene. Uniaxial tensile and compressive simulations were carried out to probe and compare stress-strain properties; such as the Young's modulus, Poisson's ratio and ultimate strength. We evaluated the chirality effect on the mechanical response and bond structure of the 2D substrates. Our first-principles simulations suggest that in all studied samples application of uniaxial loading can alter the electronic nature of the buckled structures into the metallic character. Our investigation provides a general but also useful viewpoint with respect to the mechanical properties of silicene, germanene and stanene.

  14. Surface regulated arsenenes as Dirac materials: From density functional calculations

    International Nuclear Information System (INIS)

    Yuan, Junhui; Xie, Qingxing; Yu, Niannian; Wang, Jiafu

    2017-01-01

    Highlights: • The presence of Dirac cones in chemically decorated buckled arsenene AsX (X = CN, NC, NCO, NCS, and NCSe) has been revealed. • First-principles calculations show that all these chemically decorated arsenenes are kinetically stable in defending thermal fluctuations in room temperature. - Abstract: Using first principle calculations based on density functional theory (DFT), we have systematically investigated the structure stability and electronic properties of chemically decorated arsenenes, AsX (X = CN, NC, NCO, NCS and NCSe). Phonon dispersion and formation energy analysis reveal that all the five chemically decorated buckled arsenenes are energetically favorable and could be synthesized. Our study shows that wide-bandgap arsenene would turn into Dirac materials when functionalized by -X (X = CN, NC, NCO, NCS and NCSe) groups, rendering new promises in next generation high-performance electronic devices.

  15. Quantum-mechanical calculation of H on Ni(001) using a model potential based on first-principles calculations

    DEFF Research Database (Denmark)

    Mattsson, T.R.; Wahnström, G.; Bengtsson, L.

    1997-01-01

    First-principles density-functional calculations of hydrogen adsorption on the Ni (001) surface have been performed in order to get a better understanding of adsorption and diffusion of hydrogen on metal surfaces. We find good agreement with experiments for the adsorption energy, binding distance...

  16. First-principles study of electron transport through monatomic Al and Na wires

    DEFF Research Database (Denmark)

    Kobayashi, Nobuhiko; Brandbyge, Mads; Tsukada, Masaru

    2000-01-01

    We present first-principles calculations of electron transport, in particular, the conduction channels of monatomic Al and Na atom wires bridged between metallic jellium electrodes. The electronic structures are calculated by the first-principles recursion-transfer matrix method, and the conduction...... channels are investigated using the eigenchannel decomposition (ECD) of the conductance, the local density of states (LDOS), and the current density. The ECD is different from the conventional decomposition of atomic orbitals, and the study of decomposed electronic structures is shown to be effective...

  17. Electronic Stopping Power in LiF from First Principles

    International Nuclear Information System (INIS)

    Pruneda, J. M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J. I.; Artacho, Emilio

    2007-01-01

    Using time-dependent density-functional theory we calculate from first principles the rate of energy transfer from a moving proton or antiproton to the electrons of an insulating material, LiF. The behavior of the electronic stopping power versus projectile velocity displays an effective threshold velocity of ∼0.2 a.u. for the proton, consistent with recent experimental observations, and also for the antiproton. The calculated proton/antiproton stopping-power ratio is ∼2.4 at velocities slightly above the threshold (v∼0.4 a.u.), as compared to the experimental value of 2.1. The projectile energy loss mechanism is observed to be extremely local

  18. First principles density functional calculation of magnetic moment and hyperfine fields of dilute transition metal impurities in Gd host

    International Nuclear Information System (INIS)

    Mohanta, S.K.; Mishra, S.N.; Srivastava, S.K.

    2014-01-01

    We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti–Co), 4d (Nb–Ru) and 5d (Ta–Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446–e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc–V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. - Highlights: • Detailed study of transition metal impurities in ferromagnetic Gd has been carried out. • The trends in impurity magnetic moment are qualitatively different from Fe, Co and Ni. • The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. • Experimental trend in a hyperfine field has been reproduced successfully

  19. Relationship of Quantum Entanglement to Density Functional Theory

    OpenAIRE

    Rajagopal, A. K.; Rendell, R. W.

    2005-01-01

    The maximum von Neumann entropy principle subject to given constraints of mean values of some physical observables determines the density matrix. Similarly the stationary action principle in the case of time-dependent (dissipative) situations under similar constraints yields the density matrix. The free energy and measures of entanglement are expressed in terms of such a density matrix and thus define respective functionals of the mean values. In the light of several model calculations, it is...

  20. Quantum Crystallography: Density Matrix-Density Functional Theory and the X-Ray Diffraction Experiment

    Science.gov (United States)

    Soirat, Arnaud J. A.

    Density Matrix Theory is a Quantum Mechanical formalism in which the wavefunction is eliminated and its role taken over by reduced density matrices. The interest of this is that, it allows one, in principle, to calculate any electronic property of a physical system, without having to solve the Schrodinger equation, using only two entities much simpler than an N-body wavefunction: first and second -order reduced density matrices. In practice, though, this very promising possibility faces the tremendous theoretical problem of N-representability, which has been solved for the former, but, until now, voids any hope of theoretically determining the latter. However, it has been shown that single determinant reduced density matrices of any order may be recovered from coherent X-ray diffraction data, if one provides a proper Quantum Mechanical description of the Crystallography experiment. A deeper investigation of this method is the purpose of this work, where we, first, further study the calculation of X-ray reduced density matrices N-representable by a single Slater determinant. In this context, we independently derive necessary and sufficient conditions for the uniqueness of the method. We then show how to account for electron correlation in this model. For the first time, indeed, we derive highly accurate, yet practical, density matrices approximately N-representable by correlated-determinant wavefunctions. The interest of such a result lies in the Quantum Mechanical validity of these density matrices, their property of being entirely obtainable from X-ray coherent diffraction data, their very high accuracy conferred by this known property of the N-representing wavefunction, as well as their definition as explicit functionals of the density. All of these properties are finally used in both a theoretical and a numerical application: in the former, we show that these density matrices may be used in the context of Density Functional Theory to highly accurately determine

  1. First-principles study of point defects in thorium carbide

    International Nuclear Information System (INIS)

    Pérez Daroca, D.; Jaroszewicz, S.; Llois, A.M.; Mosca, H.O.

    2014-01-01

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure

  2. First-principles study of point defects in thorium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina)

    2014-11-15

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

  3. Thermodynamics of the hexagonal close-packed iron-nitrogen system from first-principles

    DEFF Research Database (Denmark)

    Bakkedal, Morten Bjørn

    to hexagonal systems and a numerically tractable extended equation of state is developed to describe thermody-namic equilibrium properties at finite temperature.The model is applied to ε-Fe3N specifically. Through the versatility of the model, equi-librium lattice parameters, the bulk modulus, and the thermal......First-principles thermodynamic models are developed for the hexagonal close-packed ε-Fe-N system. The system can be considered as a hexagonal close-packed host lattice of iron atoms and with the nitrogen atoms residing on a sublattice formed by the octahedral interstices. The iron host lattice...... is assumed fixed.The models are developed entirely from first-principles calculations based on fundamen-tal quantum mechanical calculation through the density functional theory approach with the atomic numbers and crystal structures as the only input parameters. A complete thermody-namic description should...

  4. First Principles Simulation of a Ceramic/ Metal Interface with Misfit

    International Nuclear Information System (INIS)

    Benedek, R.; Alavi, A.; Seidman, D. N.; Yang, L. H.; Muller, D. A.; Woodward, C.

    2000-01-01

    The relaxed atomic structure of a model ceramic/metal interface, {222}MgO/Cu , is simulated, including lattice constant mismatch, using first principles local-density functional theory plane wave pseudopotential methods. The 399-atom computational unit cell contains 36 O and 49 Cu atoms per layer in accordance with the 7/6 ratio of MgO to Cu lattice constants. The atomic layers on both sides of the interface warp to optimize the local bonding. The interface adhesive energy is calculated. The interface electronic structure is found to vary appreciably with the local environment. (c) 2000 The American Physical Society

  5. First-principles real-space tight-binding LMTO calculation of electronic structures for atomic clusters

    International Nuclear Information System (INIS)

    Xie, Z.L.; Dy, K.S.; Wu, S.Y.

    1997-01-01

    A real-space scheme has been developed for a first-principles calculation of electronic structures and total energies of atomic clusters. The scheme is based on the combination of the tight-binding linear muffin-tin orbital (TBLMTO) method and the method of real-space Green close-quote s function. With this approach, the local electronic density of states can be conveniently determined from the real-space Green close-quote s function. Furthermore, the full electron density of a cluster can be directly calculated in real space. The scheme has been shown to be very efficient due to the incorporation of the method of real-space Green close-quote s function and Delley close-quote s method of evaluating multicenter integrals. copyright 1996 The American Physical Society

  6. First-principles method for electron-phonon coupling and electron mobility

    DEFF Research Database (Denmark)

    Gunst, Tue; Markussen, Troels; Stokbro, Kurt

    2016-01-01

    We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene, and MoS2. The material properties, including the electron-phonon interaction, are calculated from first principles. We provide a detailed description of the normalized full......-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell method. The method employed is fully numerical and does therefore not require a semianalytic treatment of part...... of the problem and, importantly, it keeps the anisotropy information stored in the coupling as well as the band structure. In addition, we perform calculations of the low-field mobility and its dependence on carrier density and temperature to obtain a better understanding of transport in graphene, silicene...

  7. Anisotropy and temperature dependence of structural, thermodynamic, and elastic properties of crystalline cellulose Iβ: a first-principles investigation

    Science.gov (United States)

    ShunLi Shang; Louis G. Hector Jr.; Paul Saxe; Zi-Kui Liu; Robert J. Moon; Pablo D. Zavattieri

    2014-01-01

    Anisotropy and temperature dependence of structural, thermodynamic and elastic properties of crystalline cellulose Iβ were computed with first-principles density functional theory (DFT) and a semi-empirical correction for van der Waals interactions. Specifically, we report the computed temperature variation (up to 500...

  8. Density functional theory of nuclei

    International Nuclear Information System (INIS)

    Terasaki, Jun

    2008-01-01

    The density functional theory of nuclei has come to draw attention of scientists in the field of nuclear structure because the theory is expected to provide reliable numerical data in wide range on the nuclear chart. This article is organized to present an overview of the theory to the people engaged in the theory of other fields as well as those people in the nuclear physics experiments. At first, the outline of the density functional theory widely used in the electronic systems (condensed matter, atoms, and molecules) was described starting from the Kohn-Sham equation derived on the variational principle. Then the theory used in the field of nuclear physics was presented. Hartree-Fock and Hartree-Fock-Bogolyubov approximation by using Skyrme interaction was explained. Comparison of the results of calculations and experiments of binding energies and ground state mean square charge radii of some magic number nuclei were shown. The similarity and dissimilarity between the two streams were summarized. Finally the activities of the international project of Universal Nuclear Energy Density Functional (UNEDF) which was started recently lead by US scientist was reported. This project is programmed for five years. One of the applications of the project is the calculation of the neutron capture cross section of nuclei on the r-process, which is absolutely necessary for the nucleosynthesis research. (S. Funahashi)

  9. Structural, electronic transport and optical properties of functionalized quasi-2D TiC{sub 2} from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Berdiyorov, G.R., E-mail: gberdiyorov@qf.org.qa; Madjet, M.E., E-mail: mmadjet@qf.org.qa

    2016-12-30

    Highlights: • Effect of surface termination on the optoelectronic properties of TiC{sub 2} is studied. • Fluorinated, oxidized and hydroxylated surfaces are considered. • Partial charges are calculated. • Absorption of the system increases by surface passivation. • Electronic transport reduces considerably due to the termination. - Abstract: Using the first-principles density functional theory, we study the effect of surface functionalization on the structural and optoelectronic properties of recently proposed quasi-two-dimensional material TiC{sub 2} [T. Zhao, S. Zhang, Y. Guo, Q. Wang, Nanoscale 8 (2016) 233]. Hydrogenated, fluorinated, oxidized and hydroxylated surfaces are considered. Significant changes in the lattice parameters and partial charge distributions are found due to the surface termination. Direct contribution of the adatoms to the system density of states near the Fermi level is obtained, which has a major impact on the optoelectronic properties of the material. For example, surface termination results in larger absorption in the visible range of the spectrum. The electronic transport is also affected by the surface functionalization: the current in the system can be reduced by an order of magnitude. These findings indicate the importance of the effects of surface passivation on optoelectronic properties of this quasi-2D material.

  10. A density functional study of backbone structures of polydiacetylene: destabilization of butatriene structure

    International Nuclear Information System (INIS)

    Katagiri, Hideki; Shimoi, Yukihiro; Abe, Shuji

    2004-01-01

    Backbone structures of polydiacetylene are studied with first-principles electronic structure method using plane-waves within generalized gradient approximation (GGA) of density functional theory. In spin-restricted calculations a coarse k-point sampling gives a potential energy curve with two local minima corresponding to acetylene and butatriene structures. However, the potential barrier between the two structures rapidly decreases with increasing number of k-points, which results in destabilization of the butatriene structure. Spin polarization effects also destabilize the butatriene structure, inducing atom-centered spin-density-wave state. These potential energies were compared with those obtained by Hartree-Fock, density functional within local density approximation (LDA) and GGA, and hybrid density functional methods using a gaussian basis set. The comparison shows that the density functional methods within LDA and GGA favor the destabilization of the butatriene structure in contrast to the Hartree-Fock method

  11. A first-principle for the nervous system

    OpenAIRE

    Vadakkan, Kunjumon

    2016-01-01

    Higher brain functions such as perception and memory are first-person internal sensations whose mechanisms can have options to concurrently activate motor neurons for behavioral action. By setting up all the required constraints using available information from different levels, a theoretical examination from a first-person frame of reference led to the derivation of a first-principle of the structure-function units. These units operate in synchrony with the synaptically-connected neural circ...

  12. A method of orbital analysis for large-scale first-principles simulations

    Energy Technology Data Exchange (ETDEWEB)

    Ohwaki, Tsukuru [Advanced Materials Laboratory, Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka, Kanagawa 237-8523 (Japan); Otani, Minoru [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ozaki, Taisuke [Research Center for Simulation Science (RCSS), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan)

    2014-06-28

    An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF{sub 4})

  13. A method of orbital analysis for large-scale first-principles simulations

    International Nuclear Information System (INIS)

    Ohwaki, Tsukuru; Otani, Minoru; Ozaki, Taisuke

    2014-01-01

    An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF 4 )

  14. First principles density functional theory study of Pb doped α-MnO2 catalytic materials

    Science.gov (United States)

    Song, Zilin; Yan, Zhiguo; Yang, Xiaojun; Bai, Hang; Duan, Yuhua; Yang, Bin; Leng, Li

    2018-03-01

    The impact of Pb in the tunnels of manganese oxide octahedral molecular sieves on chemical state of Mn species and lattice oxygen were investigated utilizing density functional theory calculations. The results show that the Pb dopant in the tunnels of OMS-2 could reduce the average valence states of Mn. The lower energy required for bulk oxygen defects formation in Pb-OMS-2 validates the activation of lattice oxygen by inclusion of tunnel dopant. The inclusion of Pb promotes the catalytic oxidation activity of OMS-2 by reducing the energy required for the surface lattice oxygen migration during the Mars - van Krevelen oxidation process.

  15. Engineering the work function of buckled boron α-sheet by lithium adsorption: a first-principles investigation.

    Science.gov (United States)

    Zheng, Bing; Yu, Hai-tao; Xie, Ying; Lian, Yong-fu

    2014-11-26

    First-principles density functional theory calculations were performed to study the effect of Li adsorption on the structural and electronic properties, particularly the work function, of boron α-sheet. The calculated binding energies indicated that boron α-sheet could be well stabilized by the adsorption of Li atoms. Furthermore, the work functions of Li-adsorbed boron α-sheets were observed to decrease drastically with increasing Li coverage. The work functions are lower than that of Mg and even, for some of them, lower than that of Ca, indicating a considerable potential application of Li-adsorbed boron α-sheets as field-emission and electrode materials. Based on the calculated geometric and electronic structures, we discuss in details some possible aspects affecting the work function. The Li coverage dependence of the work functions of Li-adsorbed boron α-sheets was further confirmed by electrostatic potential analyses. The relationship between the work function variation and the Fermi and vacuum energy level shifts was also discussed, and we observed that the variation of the work function is primarily associated with the shift of the Fermi energy level. It is the surface dipole formed by the interaction between adatoms and substrate that should be responsible for the observed variation of the work function, whereas the increasing negative charge and rumpling for boron α-sheet only play minor roles. Additionally, the effect of Li adatoms on the work function of boron α-sheet was confirmed to be much stronger than that of graphene or a graphene double layer.

  16. Localized surface plasmon resonance in silver nanoparticles: Atomistic first-principles time-dependent density-functional theory calculations

    OpenAIRE

    Kuisma, Mikael; Sakko, Arto; Rossi, Tuomas P.; Larsen, Ask H.; Enkovaara, Jussi; Lehtovaara, Lauri; Rantala, Tapio T.

    2015-01-01

    We observe using ab initio methods that localized surface plasmon resonances in icosahedral silver nanoparticles enter the asymptotic region already between diameters of 1 and 2 nm, converging close to the classical quasistatic limit around 3.4 eV. We base the observation on time-dependent density-functional theory simulations of the icosahedral silver clusters Ag$_{55}$ (1.06 nm), Ag$_{147}$ (1.60 nm), Ag$_{309}$ (2.14 nm), and Ag$_{561}$ (2.68 nm). The simulation method combines the adiabat...

  17. On possibility of superconductivity in SnSb: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Dabhi, Shweta D. [Department of Physics, M. K. Bhavnagar University, Bhavnagar 364001 (India); Shrivastava, Deepika [Department of Physics, Barkatullah University, Bhopal 462026 (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara 390002 (India); Sanyal, Sankar P. [Department of Physics, Barkatullah University, Bhopal 462026 (India)

    2016-09-15

    Highlights: • Superconducting property of SnSb is predicted by ab-initio calculations. • Electronic properties of SnSb in RS phase shows metallic behaviour similar to SnAs. • Phonon dispersion confirms the dynamical stability of SnSb in RS phase. • Superconducting transition temperature is 3.1 K, slightly lower than that of SnAs. • Calculated thermodynamic properties are also reported. - Abstract: The electronic, phonon structure and superconducting properties of tin antimonide (SnSb) in rock-salt (RS) structure are calculated using first-principles density functional theory. The electronic band structure and density of states show metallic behavior. The phonon frequencies are positive throughout the Brillouin zone in rock-salt structure indicating its stability in that phase. Superconductivity of SnSb in RS phase is discussed in detail by calculating phonon linewidths, Eliashberg spectral function, electron-phonon coupling constant and superconducting transition temperature. SnSb is found to have a slightly lower T{sub C} (3.1 K), as compared to SnAs.

  18. Density-functional theory for internal magnetic fields

    Science.gov (United States)

    Tellgren, Erik I.

    2018-01-01

    A density-functional theory is developed based on the Maxwell-Schrödinger equation with an internal magnetic field in addition to the external electromagnetic potentials. The basic variables of this theory are the electron density and the total magnetic field, which can equivalently be represented as a physical current density. Hence, the theory can be regarded as a physical current density-functional theory and an alternative to the paramagnetic current density-functional theory due to Vignale and Rasolt. The energy functional has strong enough convexity properties to allow a formulation that generalizes Lieb's convex analysis formulation of standard density-functional theory. Several variational principles as well as a Hohenberg-Kohn-like mapping between potentials and ground-state densities follow from the underlying convex structure. Moreover, the energy functional can be regarded as the result of a standard approximation technique (Moreau-Yosida regularization) applied to the conventional Schrödinger ground-state energy, which imposes limits on the maximum curvature of the energy (with respect to the magnetic field) and enables construction of a (Fréchet) differentiable universal density functional.

  19. First-principles study of the electronic transport properties of the anthraquinone-based molecular switch

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, P., E-mail: ss_zhaop@ujn.edu.c [School of Science, University of Jinan, Jinan 250022 (China); Liu, D.S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China); Wang, P.J.; Zhang, Z. [School of Science, University of Jinan, Jinan 250022 (China); Fang, C.F.; Ji, G.M. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)

    2011-02-15

    By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

  20. First-principles study of the electronic transport properties of the anthraquinone-based molecular switch

    International Nuclear Information System (INIS)

    Zhao, P.; Liu, D.S.; Wang, P.J.; Zhang, Z.; Fang, C.F.; Ji, G.M.

    2011-01-01

    By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

  1. Density functional theory for field emission from carbon nano-structures.

    Science.gov (United States)

    Li, Zhibing

    2015-12-01

    Electron field emission is understood as a quantum mechanical many-body problem in which an electronic quasi-particle of the emitter is converted into an electron in vacuum. Fundamental concepts of field emission, such as the field enhancement factor, work-function, edge barrier and emission current density, will be investigated, using carbon nanotubes and graphene as examples. A multi-scale algorithm basing on density functional theory is introduced. We will argue that such a first principle approach is necessary and appropriate for field emission of nano-structures, not only for a more accurate quantitative description, but, more importantly, for deeper insight into field emission. Copyright © 2015 The Author. Published by Elsevier B.V. All rights reserved.

  2. First-principles calculations of a high-pressure synthesized compound PtC

    International Nuclear Information System (INIS)

    Li Linyan; Yu Wen; Jin Changqing

    2005-01-01

    The first-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that platinum carbide has a zinc-blende ground-state phase at zero pressure and that the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt structure is determined to be 52 GPa. Furthermore, our calculation shows the possibility that the PtC experimentally synthesized under high pressure conditions might undergo a transition from rock-salt to zinc-blende structure after a pressure quench to ambient conditions

  3. First principles calculations for liquids and solids using maximally localized Wannier functions

    Science.gov (United States)

    Swartz, Charles W., VI

    The field of condensed matter computational physics has seen an explosion of applicability over the last 50+ years. Since the very first calculations with ENIAC and MANIAC the field has continued to pushed the boundaries of what is possible; from the first large-scale molecular dynamics simulation, to the implementation of Density Functional Theory and large scale Car-Parrinello molecular dynamics, to million-core turbulence calculations by Standford. These milestones represent not only technological advances but theoretical breakthroughs and algorithmic improvements as well. The work in this thesis was completed in the hopes of furthering such advancement, even by a small fraction. Here we will focus mainly on the calculation of electronic and structural properties of solids and liquids, where we shall implement a wide range of novel approaches that are both computational efficient and physically enlightening. To this end we routinely will work with maximally localized Wannier functions (MLWFs) which have recently seen a revival in mainstream scientific literature. MLWFs present us with interesting opportunity to calculate a localized orbital within the planewave formalism of atomistic simulations. Such a localization will prove to be invaluable in the construction of layer-based superlattice models, linear scaling hybrid functional schemes and model quasiparticle calculations. In the first application of MLWF we will look at modeling functional piezoelectricity in superlattices. Based on the locality principle of insulating superlattices, we apply the method of Wu et al to the piezoelectric strains of individual layers under iifixed displacement field. For a superlattice of arbitrary stacking sequence an accurate model is acquired for predicting piezoelectricity. By applying the model in the superlattices where ferroelectric and antiferrodistortive modes are in competition, functional piezoelectricity can be achieved. A strong nonlinear effect is observed and can

  4. First-principle calculation of refractive indices of BAlN and BGaN

    KAUST Repository

    Alqatari, Feras; Li, Kuang-Hui; Liu, Kaikai; Li, Xiaohang

    2018-01-01

    The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

  5. First principles calculations for interaction of tyrosine with (ZnO)3 cluster

    Science.gov (United States)

    Singh, Satvinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

    2018-04-01

    First Principles Calculations have been performed to study interactions of Phenol ring of Tyrosine (C6H5OH) with (ZnO)3 atomic cluster. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/C6H5OH have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations. The compatibility of the results with previous studies has been presented here.

  6. First-principle calculation of refractive indices of BAlN and BGaN

    KAUST Repository

    Alqatari, Feras

    2018-03-27

    The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

  7. First-principles calculation on electronic properties of zinc oxide by zinc–air system

    Directory of Open Access Journals (Sweden)

    Ahmad Azmin Mohamad

    2017-07-01

    Full Text Available First-principles calculations are performed to study the electronic properties of zinc oxide (ZnO formed on an anode after discharging a Zn–air system. Prior to calculation, the ZnO is characterised by X-ray diffraction using Rietveld refinement. Diffracted patterns proved the formation of single phase ZnO, while Rietveld analysis shows that the ZnO has a hexagonal wurtzite structure with lattice parameters, a = 3.244 and c = 5.199 Å. Geometry optimisation of the hexagonal wurtzite structure of the ZnO is performed using various exchange–correlation energy functionals. The local density approximation functional method is used to explain the structure, electronic band structure and density of state properties of hexagonal ZnO. The calculated energy band gap was 0.75 eV while the density of states reveals that the O 2p (the top valence band and Zn 4s (the bottom conduction band states domination.

  8. A first-principles approach to finite temperature elastic constants

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K [Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802 (United States)

    2010-06-09

    A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni{sub 3}Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.

  9. A first-principles approach to finite temperature elastic constants

    International Nuclear Information System (INIS)

    Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K

    2010-01-01

    A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni 3 Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.

  10. The structural, mechanical, and electronic properties of LiAlB{sub 4} under pressure from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Tayran, Ceren; Aydin, Sezgin [Department of Physics, Sciences Faculty, Gazi University, 06500, Ankara (Turkey)

    2017-05-15

    The structural, elastic, mechanical, and electronic properties of lithium aluminum tetraboride (LiAlB{sub 4}) under hydrostatic pressure have been investigated by using first-principles density functional theory calculations. The effects of pressure on the lattice parameters, volume, and bond lengths are studied. It is indicated from the calculated elastic constants that LiAlB{sub 4} compound is mechanically stable on 0-40 GPa pressure range. And, by means of these elastic constants set, some mechanical properties such as bulk, shear and Young's moduli, and then Poisson's ratio are determined as a function of pressure. Also, the ductile or brittle nature of LiAlB{sub 4} is examined. Additionally, using the first-principles data obtained from the geometry optimizations, the hardness of LiAlB{sub 4} is calculated, and its nature is investigated under pressure. Furthermore, in order to reveal the effects of pressure on the electronic and binding behavior of the compound, band structures, total and partial density of states, charge densities, Mulliken atomic charges, and bond overlap populations are searched as a function of pressure. To check the stability of the compound, phonon dispersion curves are calculated. And, the results are compared with the other convenient borides. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Analysis of wind speed distributions: Wind distribution function derived from minimum cross entropy principles as better alternative to Weibull function

    International Nuclear Information System (INIS)

    Kantar, Yeliz Mert; Usta, Ilhan

    2008-01-01

    In this study, the minimum cross entropy (MinxEnt) principle is applied for the first time to the wind energy field. This principle allows the inclusion of previous information of a wind speed distribution and covers the maximum entropy (MaxEnt) principle, which is also discussed by Li and Li and Ramirez as special cases in their wind power study. The MinxEnt probability density function (pdf) derived from the MinxEnt principle are used to determine the diurnal, monthly, seasonal and annual wind speed distributions. A comparison between MinxEnt pdfs defined on the basis of the MinxEnt principle and the Weibull pdf on wind speed data, which are taken from different sources and measured in various regions, is conducted. The wind power densities of the considered regions obtained from Weibull and MinxEnt pdfs are also compared. The results indicate that the pdfs derived from the MinxEnt principle fit better to a variety of measured wind speed data than the conventionally applied empirical Weibull pdf. Therefore, it is shown that the MinxEnt principle can be used as an alternative method to estimate both wind distribution and wind power accurately

  12. Metal-functionalized single-walled graphitic carbon nitride nanotubes: a first-principles study on magnetic property

    Directory of Open Access Journals (Sweden)

    Shenoy Vivek

    2011-01-01

    Full Text Available Abstract The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage.

  13. First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

    Directory of Open Access Journals (Sweden)

    Donato Belmonte

    2017-09-01

    Full Text Available Ab initio thermodynamic properties, equation of state and phase stability of periclase (MgO, B1-type structure have been investigated in a broad P–T range (0–160 GPa; 0–3000 K in order to set a model reference system for phase equilibria simulations under deep Earth conditions. Phonon dispersion calculations performed on large supercells using the finite displacement method and in the framework of quasi-harmonic approximation highlight the performance of the Becke three-parameter Lee-Yang-Parr (B3LYP hybrid density functional in predicting accurate thermodynamic functions (heat capacity, entropy, thermal expansivity, isothermal bulk modulus and phase reaction boundaries at high pressure and temperature. A first principles Mie–Grüneisen equation of state based on lattice vibrations directly provides a physically-consistent description of thermal pressure and P–V–T relations without any need to rely on empirical parameters or other phenomenological formalisms that could give spurious anomalies or uncontrolled extrapolations at HP–HT. The post-spinel phase transformation, Mg2SiO4 (ringwoodite = MgO (periclase + MgSiO3 (bridgmanite, is taken as a computational example to illustrate how first principles theory combined with the use of hybrid functionals is able to provide sound results on the Clapeyron slope, density change and P–T location of equilibrium mineral reactions relevant to mantle dynamics.

  14. Semiconductor band alignment from first principles: a new nonequilibrium Green's function method applied to the CZTSe/CdS interface for photovoltaics

    DEFF Research Database (Denmark)

    Palsgaard, Mattias Lau Nøhr; Crovetto, Andrea; Gunst, Tue

    2016-01-01

    In this paper we present a method to obtain the band offset of semiconductor heterointerfaces from Density Functional Theory together with the nonequilibrium Green's function method. Band alignment and detailed properties of the interface between Cu2ZnSnSe4 and CdS are extracted directly from first...... principles simulations. The interface is important for photovoltaics applications where in particular the band offsets are important for efficiency. The band bending pose a problem for accurate atomistic simulations of band offsets due to its long range. Here we investigate two different methods for dealing...... with band bending directly. One involves doping the materials to induce a shorter screening length. The other method is to apply a voltage bias across the interface to correct for the band bending. The calculated band offsets agree well with previous experimental and theoretical studies and, interestingly...

  15. First-principles calculations of the electronic and structural properties of GaSb

    Energy Technology Data Exchange (ETDEWEB)

    Castaño-González, E.-E. [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Seña, N. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mendoza-Estrada, V.; González-Hernández, R., E-mail: rhernandezj@uninorte.edu.co [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Dussan, A. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mesa, F., E-mail: fredy.mesa@urosario.edu.co [Universidad del Rosario, Grupo NanoTech, Facultad de Ciencias Naturales y Matemáticas (Colombia)

    2016-10-15

    In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B{sub 0}); while for the cohesive energy (E{sub coh}), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.

  16. First-principles studies on the adsorption of molecular oxygen on Ba(110) surface

    International Nuclear Information System (INIS)

    Li, S.F.; Xue Xinlian; Li Pinglin; Li Xinjian; Jia Yu

    2006-01-01

    The adsorption of O 2 on Ba(110) surface is studied with first-principles calculations based on density functional theory. Our calculations predict that O 2 may prefer to dissociative adsorption on Ba(110) surface without obvious barrier. Also our results do not support the model of charge transfer from the surface to the molecule as a bond breaking mechanism. Instead, the increasing hybridization between O 2 orbitals and the d states of Ba(110) surface may play an important role in the dissociation adsorption

  17. ONETEP: linear-scaling density-functional theory with plane-waves

    International Nuclear Information System (INIS)

    Haynes, P D; Mostof, A A; Skylaris, C-K; Payne, M C

    2006-01-01

    This paper provides a general overview of the methodology implemented in onetep (Order-N Electronic Total Energy Package), a parallel density-functional theory code for largescale first-principles quantum-mechanical calculations. The distinctive features of onetep are linear-scaling in both computational effort and resources, obtained by making well-controlled approximations which enable simulations to be performed with plane-wave accuracy. Titanium dioxide clusters of increasing size designed to mimic surfaces are studied to demonstrate the accuracy and scaling of onetep

  18. Functional Capillary Density Decreases after the First Week of Life in Term Neonates

    NARCIS (Netherlands)

    Top, A. P. C.; van Dijk, M.; van Velzen, J. E.; Ince, C.; Tibboel, D.

    2010-01-01

    Background: Changes in the microcirculation have been recognized to play a crucial role in many disease processes. In premature neonates, functional capillary density (FCD) decreases during the first months of life. Objectives: The aims of this study were to obtain microcirculatory parameters in

  19. Functional capillary density decreases after the first week of life in term neonates

    NARCIS (Netherlands)

    A.P.C. Top (Anke); M. van Dijk (Monique); J.E. van Velzen; C. Ince (Can); D. Tibboel (Dick)

    2010-01-01

    textabstractBackground: Changes in the microcirculation have been recognized to play a crucial role in many disease processes. In premature neonates, functional capillary density (FCD) decreases during the first months of life. Objectives: The aims of this study were to obtain microcirculatory

  20. Stability, electronic and thermodynamic properties of aluminene from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Junhui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Yu, Niannian [School of Science, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Xue, Kanhao, E-mail: xkh@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

    2017-07-01

    Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.

  1. Stability, electronic and thermodynamic properties of aluminene from first-principles calculations

    International Nuclear Information System (INIS)

    Yuan, Junhui; Yu, Niannian; Xue, Kanhao; Miao, Xiangshui

    2017-01-01

    Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.

  2. First-principles theory of inelastic currents in a scanning tunneling microscope

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.

    1998-01-01

    A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due...... to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent...

  3. First principles molecular dynamics without self-consistent field optimization

    International Nuclear Information System (INIS)

    Souvatzis, Petros; Niklasson, Anders M. N.

    2014-01-01

    We present a first principles molecular dynamics approach that is based on time-reversible extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] in the limit of vanishing self-consistent field optimization. The optimization-free dynamics keeps the computational cost to a minimum and typically provides molecular trajectories that closely follow the exact Born-Oppenheimer potential energy surface. Only one single diagonalization and Hamiltonian (or Fockian) construction are required in each integration time step. The proposed dynamics is derived for a general free-energy potential surface valid at finite electronic temperatures within hybrid density functional theory. Even in the event of irregular functional behavior that may cause a dynamical instability, the optimization-free limit represents a natural starting guess for force calculations that may require a more elaborate iterative electronic ground state optimization. Our optimization-free dynamics thus represents a flexible theoretical framework for a broad and general class of ab initio molecular dynamics simulations

  4. First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling

    Science.gov (United States)

    Jiang, Fengzhou; Yang, Lei; Zhou, Dali; He, Gang; Zhou, Jiabei; Wang, Fanhou; Chen, Zhi-Gang

    2018-04-01

    Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.

  5. Chemical hardness and density functional theory

    Indian Academy of Sciences (India)

    Unknown

    RALPH G PEARSON. Chemistry Department, University of California, Santa Barbara, CA 93106, USA. Abstract. The concept of chemical hardness is reviewed from a personal point of view. Keywords. Hardness; softness; hard & soft acids bases (HSAB); principle of maximum hardness. (PMH) density functional theory (DFT) ...

  6. Heating electrons with ion irradiation: A first-principles approach

    International Nuclear Information System (INIS)

    Pruneda, J.M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J.I.; Artacho, E.

    2009-01-01

    Using time-dependent density functional theory we calculate from first-principles the rate of energy transfer from a moving charged particle to the electrons in an insulating material. The behavior of the electronic stopping power in LiF (a wide band gap insulator) versus projectile velocity displays an effective threshold velocity of 8.2 Bohr/asec for the proton, consistent with recent experimental observations. The calculated proton/antiproton stopping power ratio is 2.4 at velocities slightly above the threshold (16.5 Bohr/asec) as compared to the experimental value of 2.1. The approximations introduced in this new non-perturbative methodology are discussed, and results on the velocity dependence of the stopping power, the locality of the energy transfer, and other characteristics of the host material are presented.

  7. First-principles investigations of the physical properties of binary uranium silicide alloys

    International Nuclear Information System (INIS)

    Yang, Jin; Long, Jianping; Yang, Lijun; Li, Dongmei

    2013-01-01

    Graphical abstract: Total density of states for USi 2 . Display Omitted -- Abstract: The structural, elastic properties and the Debye temperature of binary Uranium Silicide (U-Si) alloys are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The ground states properties are found to agree with the available experimental data. The mechanical properties like shear modulus, Young’s modulus, Poisson’s ratio σ and ratio B/G are also calculated. Finally, The averaged sound velocity (v m ), the longitudinal sound velocity (v l ), transverse sound velocity (v t ) and the Debye temperature (θ D ) are obtained. However, the theoretical values are slightly different from few existed experiment data because the latter was obtained at room temperature while the former one at 0 K

  8. First principles DFT study of dye-sensitized CdS quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Kalpna; Singh, Kh. S. [Department of Physics, D. J. College, Baraut -250611, U.P. (India); Kishor, Shyam, E-mail: shyam387@gmail.com [Department of Chemistry, J. V. College, Baraut -250611, U.P. (India); Josefesson, Ida; Odelius, Michael [Fysikum, Albanova University Center, Stockholm University, S-106 91 Stockholm (Sweden); Ramaniah, Lavanya M. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)

    2014-04-24

    Dye-sensitized quantum dots (QDs) are considered promising candidates for dye-sensitized solar cells. In order to maximize their efficiency, detailed theoretical studies are important. Here, we report a first principles density functional theory (DFT) investigation of experimentally realized dye - sensitized QD / ligand systems, viz., Cd{sub 16}S{sub 16}, capped with acetate molecules and a coumarin dye. The hybrid B3LYP functional and a 6−311+G(d,p)/LANL2dz basis set are used to study the geometric, energetic and electronic properties of these clusters. There is significant structural rearrangement in all the clusters studied - on the surface for the bare QD, and in the positions of the acetate / dye ligands for the ligated QDs. The density of states (DOS) of the bare QD shows states in the band gap, which disappear on surface passivation with the acetate molecules. Interestingly, in the dye-sensitised QD, the HOMO is found to be localized mainly on the dye molecule, while the LUMO is on the QD, as required for photo-induced electron injection from the dye to the QD.

  9. Diffusion coefficients of alloying elements in dilute Mg alloys: A comprehensive first-principles study

    International Nuclear Information System (INIS)

    Zhou, Bi-Cheng; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui

    2016-01-01

    First-principles calculations based on density functional theory have been used to calculate the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg by combining transition state theory and an 8-frequency model. The minimum energy pathways and the saddle point configurations during solute migration are calculated with the climbing image nudged elastic band method. Vibrational properties are obtained using the quasi-harmonic Debye model with inputs from first-principles calculations. An improved generalized gradient approximation of PBEsol is used in the present first-principles calculations, which is able to well describe both vacancy formation energies and vibrational properties. It is found that the solute diffusion coefficients in hcp Mg are roughly inversely proportional to the bulk modulus of the dilute alloys, which reflects the solutes' bonding to Mg. Transition metal elements with d electrons show strong interactions with Mg and have large diffusion activation energies. Correlation effects are not negligible for solutes Ca, Na, Sr, Se, Te, and Y, in which the direct solute migration barriers are much smaller than the solvent (Mg) migration barriers. Calculated diffusion coefficients are in remarkable agreement with available experimental data in the literature.

  10. First principles studies of multiferroic materials

    International Nuclear Information System (INIS)

    Picozzi, Silvia; Ederer, Claude

    2009-01-01

    Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO 3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO 3 , ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO 3 ), the magnetically induced ferroelectric polarization can be as large as a few μC cm -2 . The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the

  11. Anisotropic elastic and thermal properties of titanium borides by first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Liang; Gao, Yimin [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Xiao, Bing [Department of Physics and Quantum Theory Group, School of Science and Engineering, Tulane University, New Orleans, LA 70118 (United States); Li, Yefei, E-mail: yefeili@126.com [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Guoliang [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China)

    2013-12-05

    Highlights: •Elastic properties of titanium borides are calculated by first principles calculation. •Thermodynamical stability of titanium borides is analyzed. •Heat capacity and thermal expansion coefficient for titanium borides are calculated and compared. •Grüneisen parameters of titanium borides are calculated. -- Abstract: The anisotropic elastic and thermal expansions of the titanium borides (TiB{sub 2}, Ti{sub 3}B{sub 4}, TiB{sub P}nma and TiB{sub F}m3{sup ¯}m) are calculated from first-principles using density functional theory. All borides show different anisotropic elastic properties; the bulk, shear and Young’s moduli are consistent with those determined experimentally. The temperature dependence of thermal expansions is mainly caused by the restoration of thermal energy due to phonon excitations at low temperature. When the temperature is higher than 500 K, the volumetric coefficient is increased linearly by increasing temperature. Meanwhile, the heat capacities of titanium borides are obtained based on the knowledge of thermal expansion coefficient and the elasticity, the calculations are in good agreement with the experiments.

  12. First-principles study of hydrogen diffusion in transition metal Rhodium

    International Nuclear Information System (INIS)

    Bao, Wulijibilige; Cui, Xin; Wang, Zhi-Ping

    2015-01-01

    In this study, the diffuse pattern and path of hydrogen in transition metal rhodium are investigated by the first-principles calculations. Density functional theory is used to calculate the system energies of hydrogen atom occupying different positions in rhodium crystal lattice. The results indicate that the most stable position of hydrogen atom in rhodium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. The activation barrier energy for the diffusion of atomic hydrogen in transition metal rhodium is quantified by determining the most favorable path, i.e., the minimum-energy pathway for diffusion, that is the indirect octahedral-tetrahedral-octahedral (O-T-O) pathway, and the activation energy is 0.8345eV

  13. Density functional theory: Foundations reviewed

    Energy Technology Data Exchange (ETDEWEB)

    Kryachko, Eugene S., E-mail: eugene.kryachko@ulg.ac.be [Bogolyubov Institute for Theoretical Physics, Kiev, 03680 (Ukraine); Ludeña, Eduardo V., E-mail: popluabe@yahoo.es [Centro de Química, Instituto Venezolano de Investigaciones Científicas, IVIC, Apartado 21827, Caracas 1020-A (Venezuela, Bolivarian Republic of); Prometheus Program, Senescyt (Ecuador); Grupo Ecuatoriano para el Estudio Experimental y Teórico de Nanosistemas, GETNano, USFQ, N104-E, Quito (Ecuador); Escuela Politécnica Superior del Litoral, ESPOL, Guayaquil (Ecuador)

    2014-11-10

    Guided by the above motto (quotation), we review a broad range of issues lying at the foundations of Density Functional Theory, DFT, a theory which is currently omnipresent in our everyday computational study of atoms and molecules, solids and nano-materials, and which lies at the heart of modern many-body computational technologies. The key goal is to demonstrate that there are definitely the ways to improve DFT. We start by considering DFT in the larger context provided by reduced density matrix theory (RDMT) and natural orbital functional theory (NOFT), and examine the implications that N-representability conditions on the second-order reduced density matrix (2-RDM) have not only on RDMT and NOFT but, also, by extension, on the functionals of DFT. This examination is timely in view of the fact that necessary and sufficient N-representability conditions on the 2-RDM have recently been attained. In the second place, we review some problems appearing in the original formulation of the first Hohenberg–Kohn theorem which is still a subject of some controversy. In this vein we recall Lieb’s comment on this proof and the extension to this proof given by Pino et al. (2009), and in this context examine the conditions that must be met in order that the one-to-one correspondence between ground-state densities and external potentials remains valid for finite subspaces (namely, the subspaces where all Kohn–Sham solutions are obtained in practical applications). We also consider the issue of whether the Kohn–Sham equations can be derived from basic principles or whether they are postulated. We examine this problem in relation to ab initio DFT. The possibility of postulating arbitrary Kohn–Sham-type equations, where the effective potential is by definition some arbitrary mixture of local and non-local terms, is discussed. We also deal with the issue of whether there exists a universal functional, or whether one should advocate instead the construction of problem

  14. Covariant density functional theory: predictive power and first attempts of a microscopic derivation

    Science.gov (United States)

    Ring, Peter

    2018-05-01

    We discuss systematic global investigations with modern covariant density functionals. The number of their phenomenological parameters can be reduced considerable by using microscopic input from ab-initio calculations in nuclear matter. The size of the tensor force is still an open problem. Therefore we use the first full relativistic Brueckner-Hartree-Fock calculations in finite nuclear systems in order to study properties of such functionals, which cannot be obtained from nuclear matter calculations.

  15. First-principle calculations of the structural, electronic ...

    Indian Academy of Sciences (India)

    First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ... functional theory (DFT) combined with the quasi-harmonic .... is consistent with Vegard's law which assumes that the lat- tice constant varies .... reflects a charge-transfer effect which is due to the different.

  16. Recent progress in predicting structural and electronic properties of organic solids with the van der Waals density functional

    Energy Technology Data Exchange (ETDEWEB)

    Yanagisawa, Susumu, E-mail: shou@sci.u-ryukyu.ac.jp [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Okuma, Koji; Inaoka, Takeshi [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Hamada, Ikutaro, E-mail: Hamada.Ikutaro@nims.go.jp [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044 (Japan)

    2015-10-01

    Highlights: • Review of theoretical studies on organic solids with the density-functional methods. • van der Waals (vdW)-inclusive methods to predict cohesive properties of oligoacenes. • A variant of the vdW density functional describes the structures accurately. • The molecular configuration and conformation crucially affects the band dispersion. - Abstract: We review recent studies on electronic properties of the organic solids with the first-principles electronic structure methods, with the emphasis on the roles of the intermolecular van der Waals (vdW) interaction in electronic properties of the organic semiconductors. After a brief summary of the recent vdW inclusive first-principle theoretical methods, we discuss their performance in predicting cohesive properties of oligoacene crystals as examples of organic crystals. We show that a variant of the van der Waals density functional describes structure and energetics of organic crystals accurately. In addition, we review our recent study on the zinc phthalocyanine crystal and discuss the importance of the intermolecular distance and orientational angle in the band dispersion. Finally, we draw some general conclusions and the future perspectives.

  17. Recent progress in predicting structural and electronic properties of organic solids with the van der Waals density functional

    International Nuclear Information System (INIS)

    Yanagisawa, Susumu; Okuma, Koji; Inaoka, Takeshi; Hamada, Ikutaro

    2015-01-01

    Highlights: • Review of theoretical studies on organic solids with the density-functional methods. • van der Waals (vdW)-inclusive methods to predict cohesive properties of oligoacenes. • A variant of the vdW density functional describes the structures accurately. • The molecular configuration and conformation crucially affects the band dispersion. - Abstract: We review recent studies on electronic properties of the organic solids with the first-principles electronic structure methods, with the emphasis on the roles of the intermolecular van der Waals (vdW) interaction in electronic properties of the organic semiconductors. After a brief summary of the recent vdW inclusive first-principle theoretical methods, we discuss their performance in predicting cohesive properties of oligoacene crystals as examples of organic crystals. We show that a variant of the van der Waals density functional describes structure and energetics of organic crystals accurately. In addition, we review our recent study on the zinc phthalocyanine crystal and discuss the importance of the intermolecular distance and orientational angle in the band dispersion. Finally, we draw some general conclusions and the future perspectives.

  18. Determination of structure and properties of molecular crystals from first principles.

    Science.gov (United States)

    Szalewicz, Krzysztof

    2014-11-18

    CONSPECTUS: Until recently, it had been impossible to predict structures of molecular crystals just from the knowledge of the chemical formula for the constituent molecule(s). A solution of this problem has been achieved using intermolecular force fields computed from first principles. These fields were developed by calculating interaction energies of molecular dimers and trimers using an ab initio method called symmetry-adapted perturbation theory (SAPT) based on density-functional theory (DFT) description of monomers [SAPT(DFT)]. For clusters containing up to a dozen or so atoms, interaction energies computed using SAPT(DFT) are comparable in accuracy to the results of the best wave function-based methods, whereas the former approach can be applied to systems an order of magnitude larger than the latter. In fact, for monomers with a couple dozen atoms, SAPT(DFT) is about equally time-consuming as the supermolecular DFT approach. To develop a force field, SAPT(DFT) calculations are performed for a large number of dimer and possibly also trimer configurations (grid points in intermolecular coordinates), and the interaction energies are then fitted by analytic functions. The resulting force fields can be used to determine crystal structures and properties by applying them in molecular packing, lattice energy minimization, and molecular dynamics calculations. In this way, some of the first successful determinations of crystal structures were achieved from first principles, with crystal densities and lattice parameters agreeing with experimental values to within about 1%. Crystal properties obtained using similar procedures but empirical force fields fitted to crystal data have typical errors of several percent due to low sensitivity of empirical fits to interactions beyond those of the nearest neighbors. The first-principles approach has additional advantages over the empirical approach for notional crystals and cocrystals since empirical force fields can only be

  19. Magnetic fields and density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Salsbury Jr., Freddie [Univ. of California, Berkeley, CA (United States)

    1999-02-01

    A major focus of this dissertation is the development of functionals for the magnetic susceptibility and the chemical shielding within the context of magnetic field density functional theory (BDFT). These functionals depend on the electron density in the absence of the field, which is unlike any other treatment of these responses. There have been several advances made within this theory. The first of which is the development of local density functionals for chemical shieldings and magnetic susceptibilities. There are the first such functionals ever proposed. These parameters have been studied by constructing functionals for the current density and then using the Biot-Savart equations to obtain the responses. In order to examine the advantages and disadvantages of the local functionals, they were tested numerically on some small molecules.

  20. Magnetic fields and density functional theory

    International Nuclear Information System (INIS)

    Salsbury, Freddie Jr.

    1999-01-01

    A major focus of this dissertation is the development of functionals for the magnetic susceptibility and the chemical shielding within the context of magnetic field density functional theory (BDFT). These functionals depend on the electron density in the absence of the field, which is unlike any other treatment of these responses. There have been several advances made within this theory. The first of which is the development of local density functionals for chemical shieldings and magnetic susceptibilities. There are the first such functionals ever proposed. These parameters have been studied by constructing functionals for the current density and then using the Biot-Savart equations to obtain the responses. In order to examine the advantages and disadvantages of the local functionals, they were tested numerically on some small molecules

  1. The density functional theory and the charged fluid molecular dynamics

    International Nuclear Information System (INIS)

    Hansen, J.P.; Zerah, G.

    1993-01-01

    Car and Parrinello had the idea of combining the density functional theory (Hohenberg, Kohn and Sham) to the 'molecular dynamics' numerical modelling method, in order to simulate metallic or co-valent solids and liquids from the first principles. The objective of this paper is to present a simplified version of this method ab initio, applicable to classical and quantal charged systems. The method is illustrated with recent results on charged colloidal suspensions and highly correlated electron-proton plasmas. 1 fig., 21 refs

  2. Pressure induced structural phase transition in solid oxidizer KClO3: A first-principles study

    Science.gov (United States)

    Yedukondalu, N.; Ghule, Vikas D.; Vaitheeswaran, G.

    2013-05-01

    High pressure behavior of potassium chlorate (KClO3) has been investigated from 0 to 10 GPa by means of first principles density functional theory calculations. The calculated ground state parameters, transition pressure, and phonon frequencies using semiempirical dispersion correction scheme are in excellent agreement with experiment. It is found that KClO3 undergoes a pressure induced first order phase transition with an associated volume collapse of 6.4% from monoclinic (P21/m) → rhombohedral (R3m) structure at 2.26 GPa, which is in good accord with experimental observation. However, the transition pressure was found to underestimate (0.11 GPa) and overestimate (3.57 GPa) using local density approximation and generalized gradient approximation functionals, respectively. Mechanical stability of both the phases is explained from the calculated single crystal elastic constants. In addition, the zone center phonon frequencies have been calculated using density functional perturbation theory at ambient as well as at high pressure and the lattice modes are found to soften under pressure between 0.6 and 1.2 GPa. The present study reveals that the observed structural phase transition leads to changes in the decomposition mechanism of KClO3 which corroborates with the experimental results.

  3. Covariant density functional theory: predictive power and first attempts of a microscopic derivation

    Directory of Open Access Journals (Sweden)

    Ring Peter

    2018-01-01

    Full Text Available We discuss systematic global investigations with modern covariant density functionals. The number of their phenomenological parameters can be reduced considerable by using microscopic input from ab-initio calculations in nuclear matter. The size of the tensor force is still an open problem. Therefore we use the first full relativistic Brueckner-Hartree-Fock calculations in finite nuclear systems in order to study properties of such functionals, which cannot be obtained from nuclear matter calculations.

  4. Electronic structure and ionicity of actinide oxides from first principles

    DEFF Research Database (Denmark)

    Petit, Leon; Svane, Axel; Szotek, Z.

    2010-01-01

    The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, whi...

  5. Mechanical, electronic, chemical bonding and optical properties of cubic BaHfO3: First-principles calculations

    International Nuclear Information System (INIS)

    Liu Qijun; Liu Zhengtang; Feng Liping; Tian Hao

    2010-01-01

    We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, mechanical, electronic, chemical bonding and optical properties of cubic BaHfO 3 . The calculated lattice parameter and independent elastic constants are in good agreement with previous theoretical and experimental work. The bulk, shear and Young's modulus, Poisson coefficient, compressibility and Lame constants are obtained using Voigt-Reuss-Hill method and the Debye temperature is estimated using Debye-Grueneisen model, which are consistent with previous results. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions of cubic BaHfO 3 , the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. Then, we have explained the origins of spectral peaks on the basis of the theory of crystal-field and molecular-orbital bonding.

  6. First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT)

    International Nuclear Information System (INIS)

    Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Kasai, Hideaki; Dipojono, Hermawan Kresno

    2012-01-01

    The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H 2 O/Li-MMT.

  7. First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT).

    Science.gov (United States)

    Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Dipojono, Hermawan Kresno; Kasai, Hideaki

    2012-11-28

    The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.

  8. Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials

    International Nuclear Information System (INIS)

    Klepeis, J E

    2006-01-01

    This paper provides an introduction for non-experts to first-principles electronic structure methods that are widely used in condensed-matter physics. Particular emphasis is placed on giving the appropriate background information needed to better appreciate the use of these methods to study actinide and other materials. Specifically, I describe the underlying theory sufficiently to enable an understanding of the relative strengths and weaknesses of the methods. I also explain the meaning of commonly used terminology, including density functional theory (DFT), local density approximation (LDA), and generalized gradient approximation (GGA), as well as linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods. I also briefly discuss methodologies that extend the basic theory to address specific limitations. Finally, I describe a few illustrative applications, including quantum molecular dynamics (QMD) simulations and studies of surfaces, impurities, and defects. I conclude by addressing the current controversy regarding magnetic calculations for actinide materials

  9. Rectification of graphene self-switching diodes: First-principles study

    Science.gov (United States)

    Ghaziasadi, Hassan; Jamasb, Shahriar; Nayebi, Payman; Fouladian, Majid

    2018-05-01

    The first principles calculations based on self-consistent charge density functional tight-binding have performed to investigate the electrical properties and rectification behavior of the graphene self-switching diodes (GSSD). The devices contained two structures called CG-GSSD and DG-GSSD which have metallic or semiconductor gates depending on their side gates have a single or double hydrogen edge functionalized. We have relaxed the devices and calculated I-V curves, transmission spectrums and maximum rectification ratios. We found that the DG-MSM devices are more favorable and more stable. Also, the DG-MSM devices have better maximum rectification ratios and current. Moreover, by changing the side gates widths and behaviors from semiconductor to metal, the threshold voltages under forward bias changed from +1.2 V to +0.3 V. Also, the maximum currents are obtained from 1.12 μA to 10.50 μA. Finally, the MSM and SSS type of all devices have minimum and maximum values of voltage threshold and maximum rectification ratios, but the 769-DG devices don't obey this rule.

  10. First-Principles Study of the Polar TiC/Ti Interface

    Institute of Scientific and Technical Information of China (English)

    Limin LIU; Shaoqing WANG; Hengqiang YE

    2003-01-01

    The interface structure, work of adhesion, and bonding character of the polar TiC/Ti interface have been examined by the first-principles density functional plane-wave pseudopotential calculations. Both Ti- and C-terminated interfaces including six different interface structures were calculated, which present quite different features. For the Ti-terminated interface, the interfacial Ti-Ti bond has a strong metallic and weak covalent character; while for the C-terminated interface, the interfacial bond is a strong polar covalent interaction between the Ti-3d and C-2p orbital.The work of adhesion of C-terminated interface is nearly 9 J/m2 stronger than that of the Ti-terminated. It is found that each termination has relatively large work of adhesion, which is consistent with other polar interfaces.

  11. Comment on "Nonuniqueness of algebraic first-order density-matrix functionals"

    Science.gov (United States)

    Gritsenko, O. V.

    2018-02-01

    Wang and Knowles (WK) [Phys. Rev. A 92, 012520 (2015), 10.1103/PhysRevA.92.012520] have given a counterexample to the conventional in reduced density-matrix functional theory representation of the second-order reduced density matrix (2RDM) Γi j ,k l in the basis of the natural orbitals as a function Γi j ,k l(n ) of the orbital occupation numbers (ONs) ni. The observed nonuniqueness of Γi j ,k l for prototype systems of different symmetry has been interpreted as the inherent inability of ON functions to reproduce the 2RDM, due to the insufficient information contained in the 1RDM spectrum. In this Comment, it is argued that, rather than totally invalidating Γi j ,k l(n ) , the WK example exposes its symmetry dependence which, as well as the previously established analogous dependence in density functional theory, is demonstrated with a general formulation based on the Levy constrained search.

  12. First principle DFT study of electric field effects on the characteristics of bilayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Sabzyan, Hassan; Sadeghpour, Narges [Isfahan Univ. (Iran, Islamic Republic of). Dept. of Chemistry

    2017-04-01

    First principle density functional theory methods, local density and Perdew-Burke-Ernzerhof generalized gradient approximations with Goedecker pseudopotential (LDA-G and PBE-G), are used to study the electric field effects on the binding energy and atomic charges of bilayer graphene (BLG) at the Γ point of the Brillouin zone based on two types of unit cells (α and β) containing n{sub C}=8-32 carbon atoms. Results show that application of electric fields of 4-24 V/nm strengths reduces the binding energies and induces charge transfer between the two layers. The transferred charge increases almost linearly with the strength of the electric field for all sizes of the two types of unit cells. Furthermore, the charge transfer calculated with the α-type unit cells is more sensitive to the electric field strength. The calculated field-dependent contour plots of the differential charge densities of the two layers show details of charge density redistribution under the influence of the electric field.

  13. First-Principles Studies of Pentaerythritol Tetranitrate (PETN) Single Crystal Unit Cell Volumes and Vibrational Frequencies under Hydrostatic Pressure

    Science.gov (United States)

    Perger, Warren F.; Zhao, Jijun; Winey, J. M.; Gupta, Y. M.

    2006-07-01

    The vibrational frequencies of the PETN molecular crystal were calculated using the first-principles CRYSTAL03 program which employs an all-electron LCAO approach and calculates analytic first derivatives of the total energy with respect to atomic displacements. Numerical second derivatives were used to enable calculation of the vibrational frequencies at ambient pressure and under various states of compression. Three different density functionals, B3LYP, PW91, and X3LYP were used to examine the effect of the exchange-correlation functional on the vibrational frequencies. The average deviation with experimental results is shown to be on the order of 2-3%, depending on the functional used. The pressure-induced shift of the vibrational frequencies is presented.

  14. Investigation of structural stability and elastic properties of CrH and MnH: A first principles study

    Science.gov (United States)

    Kanagaprabha, S.; Rajeswarapalanichamy, R.; Sudhapriyanga, G.; Murugan, A.; Santhosh, M.; Iyakutti, K.

    2015-06-01

    The structural and mechanical properties of CrH and MnH are investigated using first principles calculation based on density functional theory as implemented in VASP code with generalized gradient approximation. The calculated ground state properties are in good agreement with previous experimental and other theoretical results. A structural phase transition from NaCl to NiAs phase at a pressure of 76 GPa is predicted for both CrH and MnH.

  15. Quantum Chemistry of Solids The LCAO First Principles Treatment of Crystals

    CERN Document Server

    Evarestov, Robert A

    2007-01-01

    Quantum Chemistry of Solids delivers a comprehensive account of the main features and possibilities of LCAO methods for the first principles calculations of electronic structure of periodic systems. The first part describes the basic theory underlying the LCAO methods applied to periodic systems and the use of wave-function-based (Hartree-Fock), density-based (DFT) and hybrid hamiltonians. The translation and site symmetry consideration is included to establish connection between k-space solid-state physics and real-space quantum chemistry methods in the framework of cyclic model of an infinite crystal. The inclusion of electron correlation effects for periodic systems is considered on the basis of localized crystalline orbitals. The possibilities of LCAO methods for chemical bonding analysis in periodic systems are discussed. The second part deals with the applications of LCAO methods for calculations of bulk crystal properties, including magnetic ordering and crystal structure optimization. The discussion o...

  16. Mechanical properties of layered oxysulfide CaZnOS from first principle calculations

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhi-Jun [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Feng, Ang [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai, 200050 (China); Zhang, Shao-Lin; Zhang, Wei-Bin [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Yang, Woochul, E-mail: wyang@dongguk.edu [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of)

    2016-06-15

    Elastic and tensile properties of mixed-anion oxysulfide CaZnOS have been theoretically investigated by first principle method of density functional theory (DFT). Elastic constants were obtained by stress–strain relationships, and bulk structure parameters including bulk modulus, shear modulus, as well as Poisson's ratio were then calculated using Voigt-Reuses-Hill (VRH) approximation. The results of shear anisotropic factors, compressibility anisotropic factor and directional Young's modulus showed that CaZnOS is almost elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. Chemical bond anisotropy shown by Mulliken atomic charges and bond overlap populations is responsible for the elastic anisotropy behavior aforementioned. Moreover, theoretical uniaxial and biaxial tensile results showed the crystal collapsed at strain more than 12%, except in the biaxial extension where CaZnOS collapsed at strain of 7%. - Highlights: • Elastic and theoretical tensile properties of CaZnOS have been investigated by first principle method. • CaZnOS is elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. • Mulliken atomic charges and bond overlap populations are responsible for the elastic anisotropy behavior.

  17. First-principles electronic functionalization of silicene and germanene by adatom chemisorption

    Energy Technology Data Exchange (ETDEWEB)

    Broek, B. van den; Houssa, M.; Scalise, E. [Semiconductor Physics Laboratory, Department of Physics and Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Pourtois, G. [IMEC, 75 Kapeldreef, B-3001 Leuven (Belgium); Department of Chemistry, Plasmant Research Group, University of Antwerp, B-2610 Wilrijk-Antwerp (Belgium); Afanas‘ev, V.V.; Stesmans, A. [Semiconductor Physics Laboratory, Department of Physics and Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium)

    2014-02-01

    This study presents first-principles results on the electronic functionalization of silicene and germanene monolayers by means of chemisorption of adatom species H, Li, F, Sc, Ti, V. Three general adatom-monolayer configurations are considered, each having its distinct effect on the electronic structure, yielding metallic or semiconducting dispersions depending on the adatom species and configuration. The induced bandgap is a (in)direct Γ gap ranging from 0.2 to 2.3 eV for both silicene and germanene. In general the alternating configuration was found to be the most energetically stable. The boatlike and chairlike conformers are degenerate with the former having anisotropic effective carrier masses. The top configuration leads to the planar monolayer and predominately to a gapped dispersion. The hollow configuration with V adatoms retains the Dirac cone, but with strong orbital planar hybridization at the Fermi level. We also observe a planar surface state the Fermi level for the latter systems.

  18. Diffusion in thorium carbide: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM–CNEA, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina)

    2015-12-15

    The prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature. - Highlights: • Diffusion in thorium carbide by means of first-principles calculations is studied. • The most favorable migration event is a C atom moving through a C-vacancy aided path. • Calculated C atoms diffusion coefficients agree very well with the experimental data. • For He, the energetically most favorable migration path is through Th-vacancies.

  19. Saturation and negative temperature coefficient of electrical resistivity in liquid iron-sulfur alloys at high densities from first-principles calculations

    Science.gov (United States)

    Wagle, Fabian; Steinle-Neumann, Gerd; de Koker, Nico

    2018-03-01

    We report results on electronic transport properties of liquid Fe-S alloys at conditions of planetary cores, computed using first-principle techniques in the Kubo-Greenwood formalism. We describe a combined effect of resistivity saturation due to temperature, compression, and chemistry by comparing the electron mean free path from the Drude response of optical conductivity to the mean interatomic distance. At high compression and high sulfur concentration the Ioffe-Regel condition is satisfied, and the temperature coefficient of resistivity changes sign from positive to negative. We show that this happens due to a decrease in the d density of states at the Fermi level in response to thermal broadening.

  20. Density-functional theory of atoms and molecules

    CERN Document Server

    Parr, Robert G

    1995-01-01

    Provides an account of the fundamental principles of the density-functional theory of the electronic structure of matter and its applications to atoms and molecules. This book contains a discussion of the chemical potential and its derivatives. It is intended for physicists, chemists, and advanced students in chemistry.

  1. Existence of time-dependent density-functional theory for open electronic systems: time-dependent holographic electron density theorem.

    Science.gov (United States)

    Zheng, Xiao; Yam, ChiYung; Wang, Fan; Chen, GuanHua

    2011-08-28

    We present the time-dependent holographic electron density theorem (TD-HEDT), which lays the foundation of time-dependent density-functional theory (TDDFT) for open electronic systems. For any finite electronic system, the TD-HEDT formally establishes a one-to-one correspondence between the electron density inside any finite subsystem and the time-dependent external potential. As a result, any electronic property of an open system in principle can be determined uniquely by the electron density function inside the open region. Implications of the TD-HEDT on the practicality of TDDFT are also discussed.

  2. First principles study of CaTIO3 crystal in paraelectric and ferroelectric phases

    International Nuclear Information System (INIS)

    Hashemi, H.; Kompany, A.; Hosseini, M.

    2005-01-01

    Electronic properties of CaTiO 3 crystal in paraelectric and ferroelectric phases have been studied by first principles, using Hohenberg-kohn-sham density functional theory. In paraelectric phase the results show an indirect band gap of about at 2eV at Γ-R direction in the Brillouin zone and a strong hybridization between Ti-3d an O-2P orbital. In ferroelectric phase a direct band gap of about 1 eV is seen at ***Γ point. Up to our knowledge no data has been reported on the ferroelectric phase so far, therefore our results might be useful for the future works

  3. Density-functional theory in one dimension for contact-interacting fermions

    International Nuclear Information System (INIS)

    Magyar, R.J.; Burke, K.

    2004-01-01

    A density-functional theory is developed for fermions in one dimension, interacting via a δ function. Such systems provide a natural testing ground for questions of principle, as the local-density approximation should be highly accurate since for this interaction type the exchange contribution to the local-density approximation is intrinsically self-interaction-free. The exact-exchange contribution to the total energy is a local functional of the density. A local-density approximation for correlation is obtained using perturbation theory and Bethe ansatz results for the one-dimensional contact-interacting uniform Fermi gas. The ground-state energies are calculated for two finite systems, the analogs of helium and of Hooke's atom. The local-density approximation is shown to be excellent as expected

  4. First principles calculations using density matrix divide-and-conquer within the SIESTA methodology

    International Nuclear Information System (INIS)

    Cankurtaran, B O; Gale, J D; Ford, M J

    2008-01-01

    The density matrix divide-and-conquer technique for the solution of Kohn-Sham density functional theory has been implemented within the framework of the SIESTA methodology. Implementation details are provided where the focus is on the scaling of the computation time and memory use, in both serial and parallel versions. We demonstrate the linear-scaling capabilities of the technique by providing ground state calculations of moderately large insulating, semiconducting and (near-) metallic systems. This linear-scaling technique has made it feasible to calculate the ground state properties of quantum systems consisting of tens of thousands of atoms with relatively modest computing resources. A comparison with the existing order-N functional minimization (Kim-Mauri-Galli) method is made between the insulating and semiconducting systems

  5. Unified first principles description from warm dense matter to ideal ionized gas plasma: electron-ion collisions induced friction.

    Science.gov (United States)

    Dai, Jiayu; Hou, Yong; Yuan, Jianmin

    2010-06-18

    Electron-ion interactions are central to numerous phenomena in the warm dense matter (WDM) regime and at higher temperature. The electron-ion collisions induced friction at high temperature is introduced in the procedure of ab initio molecular dynamics using the Langevin equation based on density functional theory. In this framework, as a test for Fe and H up to 1000 eV, the equation of state and the transition of electronic structures of the materials with very wide density and temperature can be described, which covers a full range of WDM up to high energy density physics. A unified first principles description from condensed matter to ideal ionized gas plasma is constructed.

  6. Site preference and phase stability of Ti doping Ni–Mn–Ga shape memory alloys from first-principles calculations

    International Nuclear Information System (INIS)

    Gao, Zhiyong; Chen, Baishu; Meng, Xianglong; Cai, Wei

    2013-01-01

    Highlights: •Site preference and phase stability of NiMnGaTi are studied by first-principles. •The Ti atoms prefer to occupy the Ga sites in the Ni 2 MnGa austenitic phase. •The phase stability becomes worse when Ga is replaced by Ti. •The phase stability is discussed based on the densities of states. -- Abstract: The effects of Ti content on martensitic transformation and phase stability of Ni 50 Mn 25 Ga 25−x Ti x shape memory alloys were investigated from first-principles calculations based on density functional theory. The formation energy results indicate that the added Ti preferentially occupies the Ga sites in Ni 2 MnGa alloy due to the lowest formation energy. The total energy difference between austenite and martensite increases with Ti alloying, being relevant to the experimentally reported changes in martensitic transformation temperature. The phase stability of Ni 50 Mn 25 Ga 25−x Ti x austenite decreases with increasing Ti content, which results from the reduced Ni 3d–Mn 3d hybridization when Ga is replaced by Ti

  7. Role of anion doping on electronic structure and magnetism of GdN by first principles calculations

    KAUST Repository

    Zhang, Xuejing; Mi, Wenbo; Guo, Zaibing; Cheng, Yingchun; Chen, Guifeng; Bai, Haili

    2014-01-01

    We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.

  8. First-principles study of SnS electronic properties using LDA, PBE and HSE06 functionals

    Science.gov (United States)

    Ibragimova, R.; Ganchenkova, M.; Karazhanov, S.; Marstein, E. S.

    2018-03-01

    Recently, tin sulphide (SnS) has emerged as a promising alternative to conventional CIGS and CZTC for use in solar cells, possessing such properties as non-toxicity, low cost and production stability. SnS has a high theoretically predicted efficiency above 20%, but the experimentally achieved efficiency so far is as low as 4.36%. The reason for the low achieved efficiency is unclear. One of the powerful tools to get deeper insights about the nature of the problem is first-principles calculation approaches. That is why SnS has become an attractive subject for first-principles calculations recently. Previously calculated data, however, show a widespread of such fundamental value as the bandgap varying from 0.26 to 1.26 eV. In order to understand a reason for that, in this work, we concentrate on a systematic study of calculation parameters effects on the resulting electronic structure, with the particular attention paid to the influence of the exchange-correlation functional chosen for calculations. Several exchange-correlation functionals (LDA, PBE and HSE06) were considered. The systematic analysis has shown that the bandgap variation can result from a tensile/compressive hydrostatic pressure introduced by non-equilibrium lattice parameters used for the calculations. The study of the applicability of three functionals has shown that HSE06 gives the best match to both experimentally obtained bandgap and the XPS valence band spectra. LDA underestimates the bandgap but qualitatively reproduces experimentally measured valence DOS similar to that of HSE06 in contrast to PBE. PBE underestimates the bandgap and does not match to the measured XPS spectra.

  9. First principles studies of complex oxide surfaces and interfaces

    International Nuclear Information System (INIS)

    Noguera, Claudine; Finocchi, Fabio; Goniakowski, Jacek

    2004-01-01

    Oxides enter our everyday life and exhibit an impressive variety of physical and chemical properties. The understanding of their behaviour, which is often determined by the electronic and atomic structures of their surfaces and interfaces, is a key question in many fields, such as geology, environmental chemistry, catalysis, thermal coatings, microelectronics, and bioengineering. In the last decade, first principles methods, mainly those based on the density functional theory, have been frequently applied to study complex oxide surfaces and interfaces, complementing the experimental observations. In this work, we discuss some of these contributions, with emphasis on several issues that are especially important when dealing with oxides: the local electronic structure at interfaces, and its connection with chemical reactivity; the charge redistribution and the bonding variations, in relation to screening properties; and the possibility of bridging the gap between model and real systems by taking into account the chemical environments and the effect of finite temperatures, and by performing simulations on systems of an adequate (large) size

  10. Obtaining Hartree-Fock and density functional theory doubly excited states with Car-Parrinello density matrix search

    Science.gov (United States)

    Liang, Wenkel; Isborn, Christine M.; Li, Xiaosong

    2009-11-01

    The calculation of doubly excited states is one of the major problems plaguing the modern day excited state workhorse methodology of linear response time dependent Hartree-Fock (TDHF) and density function theory (TDDFT). We have previously shown that the use of a resonantly tuned field within real-time TDHF and TDDFT is able to simultaneously excite both the α and β electrons to achieve the two-electron excited states of minimal basis H2 and HeH+ [C. M. Isborn and X. Li, J. Chem. Phys. 129, 204107 (2008)]. We now extend this method to many electron systems with the use of our Car-Parrinello density matrix search (CP-DMS) with a first-principles fictitious mass method for wave function optimization [X. Li, C. L. Moss, W. Liang, and Y. Feng, J. Chem. Phys. 130, 234115 (2009)]. Real-time TDHF/TDDFT is used during the application of the laser field perturbation, driving the electron density toward the doubly excited state. The CP-DMS method then converges the density to the nearest stationary state. We present these stationary state doubly excited state energies and properties at the HF and DFT levels for H2, HeH+, lithium hydride, ethylene, and butadiene.

  11. First principles calculation of thermodynamic properties of NaAlSi ternary

    International Nuclear Information System (INIS)

    Qin Jining; Lu Weijie; Zhang Di; Fan Tongxiang

    2012-01-01

    PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.

  12. Equilibration and analysis of first-principles molecular dynamics simulations of water

    Science.gov (United States)

    Dawson, William; Gygi, François

    2018-03-01

    First-principles molecular dynamics (FPMD) simulations based on density functional theory are becoming increasingly popular for the description of liquids. In view of the high computational cost of these simulations, the choice of an appropriate equilibration protocol is critical. We assess two methods of estimation of equilibration times using a large dataset of first-principles molecular dynamics simulations of water. The Gelman-Rubin potential scale reduction factor [A. Gelman and D. B. Rubin, Stat. Sci. 7, 457 (1992)] and the marginal standard error rule heuristic proposed by White [Simulation 69, 323 (1997)] are evaluated on a set of 32 independent 64-molecule simulations of 58 ps each, amounting to a combined cumulative time of 1.85 ns. The availability of multiple independent simulations also allows for an estimation of the variance of averaged quantities, both within MD runs and between runs. We analyze atomic trajectories, focusing on correlations of the Kohn-Sham energy, pair correlation functions, number of hydrogen bonds, and diffusion coefficient. The observed variability across samples provides a measure of the uncertainty associated with these quantities, thus facilitating meaningful comparisons of different approximations used in the simulations. We find that the computed diffusion coefficient and average number of hydrogen bonds are affected by a significant uncertainty in spite of the large size of the dataset used. A comparison with classical simulations using the TIP4P/2005 model confirms that the variability of the diffusivity is also observed after long equilibration times. Complete atomic trajectories and simulation output files are available online for further analysis.

  13. On extending Kohn-Sham density functionals to systems with fractional number of electrons.

    Science.gov (United States)

    Li, Chen; Lu, Jianfeng; Yang, Weitao

    2017-06-07

    We analyze four ways of formulating the Kohn-Sham (KS) density functionals with a fractional number of electrons, through extending the constrained search space from the Kohn-Sham and the generalized Kohn-Sham (GKS) non-interacting v-representable density domain for integer systems to four different sets of densities for fractional systems. In particular, these density sets are (I) ensemble interacting N-representable densities, (II) ensemble non-interacting N-representable densities, (III) non-interacting densities by the Janak construction, and (IV) non-interacting densities whose composing orbitals satisfy the Aufbau occupation principle. By proving the equivalence of the underlying first order reduced density matrices associated with these densities, we show that sets (I), (II), and (III) are equivalent, and all reduce to the Janak construction. Moreover, for functionals with the ensemble v-representable assumption at the minimizer, (III) reduces to (IV) and thus justifies the previous use of the Aufbau protocol within the (G)KS framework in the study of the ground state of fractional electron systems, as defined in the grand canonical ensemble at zero temperature. By further analyzing the Aufbau solution for different density functional approximations (DFAs) in the (G)KS scheme, we rigorously prove that there can be one and only one fractional occupation for the Hartree Fock functional, while there can be multiple fractional occupations for general DFAs in the presence of degeneracy. This has been confirmed by numerical calculations using the local density approximation as a representative of general DFAs. This work thus clarifies important issues on density functional theory calculations for fractional electron systems.

  14. Atomistic properties of helium in hcp titanium: A first-principles study

    International Nuclear Information System (INIS)

    Wang Yongli; Liu, Shi; Rong Lijian; Wang Yuanming

    2010-01-01

    First-principles calculations based on density functional theory have been performed to investigate the behaviors of He in hcp-type Ti. The most favorable interstitial site for He is not an ordinary octahedral or tetrahedral site, but a novel interstitial site (called FC) with a formation energy as low as 2.67 eV, locating the center of the face shared by two adjacent octahedrons. The origin was further analyzed by composition of formation energy of interstitial He defects and charge density of defect-free hcp Ti. It has also been found that an interstitial He atom can easily migrate along direction with an activation energy of 0.34 eV and be trapped by another interstitial He atom with a high binding energy of 0.66 eV. In addition, the small He clusters with/without Ti vacancy have been compared in details and the formation energies of He n V clusters with a pre-existing Ti vacancy are even higher than those of He n clusters until n ≥ 3.

  15. Quantal density functional theory. 2. ed.

    International Nuclear Information System (INIS)

    Sahni, Viraht

    2016-01-01

    This book is on quantal density functional theory (QDFT) which is a time-dependent local effective potential theory of the electronic structure of matter. The time-independent QDFT constitutes a special case. The 2 nd edition describes the further development of the theory, and extends it to include the presence of an external magnetostatic field. The theory is based on the 'quantal Newtonian' second and first laws for the individual electron. These laws are in terms of 'classical' fields that pervade all space, and their quantal sources. The fields are separately representative of the electron correlations that must be accounted for in local potential theory. Recent developments show that irrespective of the type of external field the electrons are subject to, the only correlations beyond those due to the Pauli exclusion principle and Coulomb repulsion that need be considered are solely of the correlation-kinetic effects. Foundational to QDFT, the book describes Schroedinger theory from the new perspective of the single electron in terms of the 'quantal Newtonian' laws. Hohenberg-Kohn density functional theory (DFT), new understandings of the theory and its extension to the presence of an external uniform magnetostatic field are described. The physical interpretation via QDFT, in terms of electron correlations, of Kohn-Sham DFT, approximations to it and Slater theory are provided.

  16. Quantal density functional theory. 2. ed.

    Energy Technology Data Exchange (ETDEWEB)

    Sahni, Viraht

    2016-07-01

    This book is on quantal density functional theory (QDFT) which is a time-dependent local effective potential theory of the electronic structure of matter. The time-independent QDFT constitutes a special case. The 2{sup nd} edition describes the further development of the theory, and extends it to include the presence of an external magnetostatic field. The theory is based on the 'quantal Newtonian' second and first laws for the individual electron. These laws are in terms of 'classical' fields that pervade all space, and their quantal sources. The fields are separately representative of the electron correlations that must be accounted for in local potential theory. Recent developments show that irrespective of the type of external field the electrons are subject to, the only correlations beyond those due to the Pauli exclusion principle and Coulomb repulsion that need be considered are solely of the correlation-kinetic effects. Foundational to QDFT, the book describes Schroedinger theory from the new perspective of the single electron in terms of the 'quantal Newtonian' laws. Hohenberg-Kohn density functional theory (DFT), new understandings of the theory and its extension to the presence of an external uniform magnetostatic field are described. The physical interpretation via QDFT, in terms of electron correlations, of Kohn-Sham DFT, approximations to it and Slater theory are provided.

  17. Sb2Te3 crystal a potential absorber material for broadband photodetector: A first-principles study

    Directory of Open Access Journals (Sweden)

    Abdullahi Lawal

    Full Text Available Antimony telluride (Sb2Te3, a layered semiconductor material, is considered a promising absorbing material for a high-performance optoelectronic device within broadband wavelengths because of remarkable features like strong optical absorbance and the narrow direct band gap. In this work, based on the first-principles approach, we investigate in detail the structural, electronic and optical properties of the hexagonal Sb2Te3 compound. The structural and electronic properties were computed using the first-principles approach, treating exchange–correlation potential with generalized gradient approximation (GGA within density functional theory (DFT. Furthermore, for accurate prediction of the band gap, we go beyond DFT and calculated band structure using GW correction. The optical properties, namely, imaginary and real parts of complex dielectric function, absorption coefficient, refractive index, reflectivity, extinction coefficient, electron energy loss function and optical conductivity are performed by quasi-particle many-body perturbation theory (MBPT via Bethe-Salpeter equation (BSE. The computed structural parameters are in good agreement with available experimental data. The obtained quasi-particle (GW correction band structure show the semiconducting character of Sb2Te3 material with a direct band gap Eg of 0.221 eV, in agreement with previously reported value (Eg = 0.210 eV while the projected density of states indicates (PDOS that the p-orbital of Sb and Te atoms are responsible for material properties near the Fermi level. To our knowledge, our first reported calculations of optical properties, with the inclusion of electron-hole effects are consistent with available experimental measurements. Consistencies of our findings with experimental data validate the effectiveness of electron-hole interaction for theoretical investigation of optical properties. Keywords: DFT, Quasi-particle many-body perturbation theory, Bethe

  18. Effects of hydrogen on Mn-doped GaN: A first principles calculation

    International Nuclear Information System (INIS)

    Wu, M.S.; Xu, B.; Liu, G.; Lei, X.L.; Ouyang, C.Y.

    2013-01-01

    First-principles calculations based on spin density functional theory are performed to study the effects of H on the structural, electronic and magnetic properties of the Mn-doped GaN dilute magnetic semiconductors. Our results show that the interstitial H atom prefers to bond with N atom rather than Mn atom, which means that H favors to form the N–H complex rather than Mn–H complex in the Mn-doped GaN. After introducing one H atom in the system, the total magnetic moment of the Mn-doped GaN increases by 25%, from 4.0μ B to 5.0μ B . The physics mechanism of the increase of magnetic moment after hydrogenation in Mn-doped GaN is discussed

  19. Exact density functional and wave function embedding schemes based on orbital localization

    International Nuclear Information System (INIS)

    Hégely, Bence; Nagy, Péter R.; Kállay, Mihály; Ferenczy, György G.

    2016-01-01

    Exact schemes for the embedding of density functional theory (DFT) and wave function theory (WFT) methods into lower-level DFT or WFT approaches are introduced utilizing orbital localization. First, a simple modification of the projector-based embedding scheme of Manby and co-workers [J. Chem. Phys. 140, 18A507 (2014)] is proposed. We also use localized orbitals to partition the system, but instead of augmenting the Fock operator with a somewhat arbitrary level-shift projector we solve the Huzinaga-equation, which strictly enforces the Pauli exclusion principle. Second, the embedding of WFT methods in local correlation approaches is studied. Since the latter methods split up the system into local domains, very simple embedding theories can be defined if the domains of the active subsystem and the environment are treated at a different level. The considered embedding schemes are benchmarked for reaction energies and compared to quantum mechanics (QM)/molecular mechanics (MM) and vacuum embedding. We conclude that for DFT-in-DFT embedding, the Huzinaga-equation-based scheme is more efficient than the other approaches, but QM/MM or even simple vacuum embedding is still competitive in particular cases. Concerning the embedding of wave function methods, the clear winner is the embedding of WFT into low-level local correlation approaches, and WFT-in-DFT embedding can only be more advantageous if a non-hybrid density functional is employed.

  20. Exact density functional and wave function embedding schemes based on orbital localization

    Science.gov (United States)

    Hégely, Bence; Nagy, Péter R.; Ferenczy, György G.; Kállay, Mihály

    2016-08-01

    Exact schemes for the embedding of density functional theory (DFT) and wave function theory (WFT) methods into lower-level DFT or WFT approaches are introduced utilizing orbital localization. First, a simple modification of the projector-based embedding scheme of Manby and co-workers [J. Chem. Phys. 140, 18A507 (2014)] is proposed. We also use localized orbitals to partition the system, but instead of augmenting the Fock operator with a somewhat arbitrary level-shift projector we solve the Huzinaga-equation, which strictly enforces the Pauli exclusion principle. Second, the embedding of WFT methods in local correlation approaches is studied. Since the latter methods split up the system into local domains, very simple embedding theories can be defined if the domains of the active subsystem and the environment are treated at a different level. The considered embedding schemes are benchmarked for reaction energies and compared to quantum mechanics (QM)/molecular mechanics (MM) and vacuum embedding. We conclude that for DFT-in-DFT embedding, the Huzinaga-equation-based scheme is more efficient than the other approaches, but QM/MM or even simple vacuum embedding is still competitive in particular cases. Concerning the embedding of wave function methods, the clear winner is the embedding of WFT into low-level local correlation approaches, and WFT-in-DFT embedding can only be more advantageous if a non-hybrid density functional is employed.

  1. Exact density functional and wave function embedding schemes based on orbital localization

    Energy Technology Data Exchange (ETDEWEB)

    Hégely, Bence; Nagy, Péter R.; Kállay, Mihály, E-mail: kallay@mail.bme.hu [MTA-BME Lendület Quantum Chemistry Research Group, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, P.O. Box 91, H-1521 Budapest (Hungary); Ferenczy, György G. [Medicinal Chemistry Research Group, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, H-1117 Budapest (Hungary); Department of Biophysics and Radiation Biology, Semmelweis University, Tűzoltó u. 37-47, H-1094 Budapest (Hungary)

    2016-08-14

    Exact schemes for the embedding of density functional theory (DFT) and wave function theory (WFT) methods into lower-level DFT or WFT approaches are introduced utilizing orbital localization. First, a simple modification of the projector-based embedding scheme of Manby and co-workers [J. Chem. Phys. 140, 18A507 (2014)] is proposed. We also use localized orbitals to partition the system, but instead of augmenting the Fock operator with a somewhat arbitrary level-shift projector we solve the Huzinaga-equation, which strictly enforces the Pauli exclusion principle. Second, the embedding of WFT methods in local correlation approaches is studied. Since the latter methods split up the system into local domains, very simple embedding theories can be defined if the domains of the active subsystem and the environment are treated at a different level. The considered embedding schemes are benchmarked for reaction energies and compared to quantum mechanics (QM)/molecular mechanics (MM) and vacuum embedding. We conclude that for DFT-in-DFT embedding, the Huzinaga-equation-based scheme is more efficient than the other approaches, but QM/MM or even simple vacuum embedding is still competitive in particular cases. Concerning the embedding of wave function methods, the clear winner is the embedding of WFT into low-level local correlation approaches, and WFT-in-DFT embedding can only be more advantageous if a non-hybrid density functional is employed.

  2. Anomalous doping effect in black phosphorene using first-principles calculations.

    Science.gov (United States)

    Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2015-07-07

    Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with an odd number of valence electrons retain a semiconducting feature. This even-odd oscillating behavior is attributed to the peculiar bonding characteristics of phosphorene and the strong hybridization of sp orbitals between dopants and phosphorene. Furthermore, the calculated formation energies of various substitutional dopants in phosphorene show that such doped systems can be thermodynamically stable. These results propose an intriguing route to tune the transport properties of electronic and photoelectronic devices based on phosphorene.

  3. Towards quantitative accuracy in first-principles transport calculations: The GW method applied to alkane/gold junctions

    DEFF Research Database (Denmark)

    Strange, Mikkel; Thygesen, Kristian Sommer

    2011-01-01

    -electron interactions are described by th=e many-body GW approximation. The conductance follows an exponential length dependence: Gn = Gc exp(-βn). The main difference from standard density functional theory (DFT) calculations is a significant reduction of the contact conductance, Gc, due to an improved alignment......The calculation of the electronic conductance of nanoscale junctions from first principles is a long-standing problem in the field of charge transport. Here we demonstrate excellent agreement with experiments for the transport properties of the gold/alkanediamine benchmark system when electron...

  4. Primordial Black Holes from First Principles (Overview)

    Science.gov (United States)

    Lam, Casey; Bloomfield, Jolyon; Moss, Zander; Russell, Megan; Face, Stephen; Guth, Alan

    2017-01-01

    Given a power spectrum from inflation, our goal is to calculate, from first principles, the number density and mass spectrum of primordial black holes that form in the early universe. Previously, these have been calculated using the Press- Schechter formalism and some demonstrably dubious rules of thumb regarding predictions of black hole collapse. Instead, we use Monte Carlo integration methods to sample field configurations from a power spectrum combined with numerical relativity simulations to obtain a more accurate picture of primordial black hole formation. We demonstrate how this can be applied for both Gaussian perturbations and the more interesting (for primordial black holes) theory of hybrid inflation. One of the tools that we employ is a variant of the BBKS formalism for computing the statistics of density peaks in the early universe. We discuss the issue of overcounting due to subpeaks that can arise from this approach (the ``cloud-in-cloud'' problem). MIT UROP Office- Paul E. Gray (1954) Endowed Fund.

  5. Near-infrared radiation absorption properties of covellite (CuS using first-principles calculations

    Directory of Open Access Journals (Sweden)

    Lihua Xiao

    2016-08-01

    Full Text Available First-principles density functional theory was used to investigate the electronic structure, optical properties and the origin of the near-infrared (NIR absorption of covellite (CuS. The calculated lattice constant and optical properties are found to be in reasonable agreement with experimental and theoretical findings. The electronic structure reveals that the valence and conduction bands of covellite are determined by the Cu 3d and S 3p states. By analyzing its optical properties, we can fully understand the potential of covellite (CuS as a NIR absorbing material. Our results show that covellite (CuS exhibits NIR absorption due to its metal-like plasma oscillation in the NIR range.

  6. The effects of the impurity distribution on the electrical and optical properties of Cr2+:ZnSe nanowires: First-principles study

    Directory of Open Access Journals (Sweden)

    Shenyu Dai

    2018-03-01

    Full Text Available The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT. The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed. Keywords: First-principles, Nanowires, Impurity distribution, Cr-doped ZnSe

  7. Grand canonical electronic density-functional theory: Algorithms and applications to electrochemistry

    International Nuclear Information System (INIS)

    Sundararaman, Ravishankar; Goddard, William A. III; Arias, Tomas A.

    2017-01-01

    First-principles calculations combining density-functional theory and continuum solvation models enable realistic theoretical modeling and design of electrochemical systems. When a reaction proceeds in such systems, the number of electrons in the portion of the system treated quantum mechanically changes continuously, with a balancing charge appearing in the continuum electrolyte. A grand-canonical ensemble of electrons at a chemical potential set by the electrode potential is therefore the ideal description of such systems that directly mimics the experimental condition. We present two distinct algorithms: a self-consistent field method and a direct variational free energy minimization method using auxiliary Hamiltonians (GC-AuxH), to solve the Kohn-Sham equations of electronic density-functional theory directly in the grand canonical ensemble at fixed potential. Both methods substantially improve performance compared to a sequence of conventional fixed-number calculations targeting the desired potential, with the GC-AuxH method additionally exhibiting reliable and smooth exponential convergence of the grand free energy. Lastly, we apply grand-canonical density-functional theory to the under-potential deposition of copper on platinum from chloride-containing electrolytes and show that chloride desorption, not partial copper monolayer formation, is responsible for the second voltammetric peak.

  8. Grand canonical electronic density-functional theory: Algorithms and applications to electrochemistry

    Science.gov (United States)

    Sundararaman, Ravishankar; Goddard, William A.; Arias, Tomas A.

    2017-03-01

    First-principles calculations combining density-functional theory and continuum solvation models enable realistic theoretical modeling and design of electrochemical systems. When a reaction proceeds in such systems, the number of electrons in the portion of the system treated quantum mechanically changes continuously, with a balancing charge appearing in the continuum electrolyte. A grand-canonical ensemble of electrons at a chemical potential set by the electrode potential is therefore the ideal description of such systems that directly mimics the experimental condition. We present two distinct algorithms: a self-consistent field method and a direct variational free energy minimization method using auxiliary Hamiltonians (GC-AuxH), to solve the Kohn-Sham equations of electronic density-functional theory directly in the grand canonical ensemble at fixed potential. Both methods substantially improve performance compared to a sequence of conventional fixed-number calculations targeting the desired potential, with the GC-AuxH method additionally exhibiting reliable and smooth exponential convergence of the grand free energy. Finally, we apply grand-canonical density-functional theory to the under-potential deposition of copper on platinum from chloride-containing electrolytes and show that chloride desorption, not partial copper monolayer formation, is responsible for the second voltammetric peak.

  9. First principles investigation of structural, vibrational and thermal properties of black and blue phosphorene

    Science.gov (United States)

    Arif Khalil, R. M.; Ahmad, Javed; Rana, Anwar Manzoor; Bukhari, Syed Hamad; Tufiq Jamil, M.; Tehreem, Tuba; Nissar, Umair

    2018-05-01

    In this investigation, structural, dynamical and thermal properties of black and blue phosphorene (P) are presented through the first principles calculations based on the density functional theory (DFT). These DFT calculations depict that due to the approximately same values of ground state energy at zero Kelvin and Helmholtz free energy at room-temperature, it is expected that both structures can coexist at transition temperature. Lattice dynamics of both phases were investigated by using the finite displacement supercell approach. It is noticed on the basis of harmonic approximation thermodynamic calculations that the blue phase is thermodynamically more stable than the black phase above 155 K.

  10. Half-metallic ferromagnetism in Fe-doped Zn3P2 from first-principles calculations

    International Nuclear Information System (INIS)

    Jaiganesh, G.; Jaya, S. Mathi

    2014-01-01

    Using the first-principles calculations based on the density functional theory, we have studied the magnetism and electronic structure of Fe-doped Zinc Phosphide (Zn 3 P 2 ). Our results show that the half-metallic ground state and ferromagnetic stability for the small Fe concentrations considered in our study. The stability of the doped material has been studied by calculating the heat of formation and analyzing the minimum total energies in nonmagnetic and ferromagnetic phases. A large value of the magnetic moment is obtained from our calculations and our calculation suggests that the Fe-doped Zn 3 P 2 may be a useful material in semiconductor spintronics

  11. First-principles study on the effect of high In doping on the conductivity of ZnO

    International Nuclear Information System (INIS)

    Hou Qing-Yu; Li Ji-Jun; Ying Chun; Zhao Chun-Wang; Zhao Er-Jun; Zhang Yue

    2013-01-01

    Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly In-doped supercells of Zn 0.9375 In 0.0625 O and Zn 0.875 In 0.125 O are constructed, and the geometry optimizations of the three models are carried out. The total density of states (DOS) and the band structures (BS) are also calculated. The calculation results show that in the range of high doping concentration, when the doping concentration is hihger than a specific value, the conductivity decreases with the increase of the doping concentration of In in ZnO, which is in consistence with the change trend of the experimental results

  12. TOPICAL REVIEW: First principles studies of multiferroic materials

    Science.gov (United States)

    Picozzi, Silvia; Ederer, Claude

    2009-07-01

    Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO3, ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO3), the magnetically induced ferroelectric polarization can be as large as a few µC cm-2. The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the

  13. Half-metallic ferromagnetism in Fe, Co and Ni doped BaS: First principles calculations

    Science.gov (United States)

    Maurya, Savita; Sharma, Ramesh; Bhamu, K. C.

    2018-04-01

    The first principle investigation of structural, electronic, magnetic and optical properties of Ba1-xTMxS (x = 0.25) have been done using FPLAW method within the density functional theory (DFT) using generalized gradient approximation (GGA) for exchange correlation potential using two different functionals which are the PBE-sol and the modified Becke and Johnson local (spin) density approximation (mBJLDA). It was found that mBJLDA functional offer better account for the electronic structure of the Fe, Co and Ni-doped BaS. It was also observed that Fe/Co/Ni d, S p and Ba d states play a major role in determining the electronic properties of this alloy system. Investigation results shows that Ba0.75(Fe/Co/Ni)0.25S is ferromagnetic with magnetic moment of 3.72 µB, 2.73908 µB and 1.74324 µB at Fe, Co and Ni sites respectively. Complex dielectric constant ɛ(ω) and normal incidence reflectivity R(ω) are also been investigate for broad range of photon energies. These results are compared with the some reported existing experimental values.

  14. First-principles calculation of transport property in nano-devices under an external magnetic field

    International Nuclear Information System (INIS)

    Chen Jingzhe; Zhang Jin; Han Rushan

    2008-01-01

    The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov–Bohm effect (A–B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A–B effect is observed and the origin of the oscillation is also discussed

  15. Jump rates for surface diffusion of large molecules from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Shea, Patrick, E-mail: patrick.shea@dal.ca; Kreuzer, Hans Jürgen [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 3J5 (Canada)

    2015-04-21

    We apply a recently developed stochastic model for the surface diffusion of large molecules to calculate jump rates for 9,10-dithioanthracene on a Cu(111) surface. The necessary input parameters for the stochastic model are calculated from first principles using density functional theory (DFT). We find that the inclusion of van der Waals corrections to the DFT energies is critical to obtain good agreement with experimental results for the adsorption geometry and energy barrier for diffusion. The predictions for jump rates in our model are in excellent agreement with measured values and show a marked improvement over transition state theory (TST). We find that the jump rate prefactor is reduced by an order of magnitude from the TST estimate due to frictional damping resulting from energy exchange with surface phonons, as well as a rotational mode of the diffusing molecule.

  16. First-principles modeling of magnetic misfit interfaces

    KAUST Repository

    Grytsiuk, Sergii

    2013-08-16

    We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.

  17. First-principles modeling of magnetic misfit interfaces

    KAUST Repository

    Grytsyuk, Sergiy; Schwingenschlö gl, Udo

    2013-01-01

    We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.

  18. A maximum principle for the first-order Boltzmann equation, incorporating a potential treatment of voids

    International Nuclear Information System (INIS)

    Schofield, S.L.

    1988-01-01

    Ackroyd's generalized least-squares method for solving the first-order Boltzmann equation is adapted to incorporate a potential treatment of voids. The adaptation comprises a direct least-squares minimization allied with a suitably-defined bilinear functional. The resulting formulation gives rise to a maximum principle whose functional does not contain terms of the type that have previously led to difficulties in treating void regions. The maximum principle is derived without requiring continuity of the flux at interfaces. The functional of the maximum principle is concluded to have an Euler-Lagrange equation given directly by the first-order Boltzmann equation. (author)

  19. First-principles investigation of strain effects on the energy gaps in silicon nanoclusters

    International Nuclear Information System (INIS)

    Peng, X-H; Alizadeh, A; Bhate, N; Varanasi, K K; Kumar, S K; Nayak, S K

    2007-01-01

    First-principles density functional calculations were performed to study strain effects on the energy gaps in silicon nanoclusters with diameter ranging from 0.6 to 2 nm. Hydrostatic and non-hydrostatic strains have been found to affect the energy gaps differently. For the same strain energy density, non-hydrostatic strain leads to a significantly larger change in the energy gap of silicon clusters compared to that of the hydrostatic strain case. In contrast, hydrostatic and non-hydrostatic strain effects on the energy gaps of bulk Si or larger size Si quantum dots are comparable. Non-hydrostatic strains break the tetrahedral bonding symmetry in silicon, resulting in significant variation in the energy gaps due to the splitting of the degenerate orbitals in the clusters. Our results suggest that the combination of energy gaps and strains permits the engineering of photoluminescence in silicon nanoclusters and offers the possibility of designing novel optical devices and chemical sensors

  20. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Schulthess, T C [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States); Temmerman, W M [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Szotek, Z [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Svane, A [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Petit, L [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States)

    2007-04-23

    We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments.

  1. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    International Nuclear Information System (INIS)

    Schulthess, T C; Temmerman, W M; Szotek, Z; Svane, A; Petit, L

    2007-01-01

    We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments

  2. Orbital functionals in density-matrix- and current-density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Helbig, N

    2006-05-15

    Density-Functional Theory (DFT), although widely used and very successful in the calculation of several observables, fails to correctly describe strongly correlated materials. In the first part of this work we, therefore, introduce reduced-densitymatrix- functional theory (RDMFT) which is one possible way to treat electron correlation beyond DFT. Within this theory the one-body reduced density matrix (1- RDM) is used as the basic variable. Our main interest is the calculation of the fundamental gap which proves very problematic within DFT. In order to calculate the fundamental gap we generalize RDMFT to fractional particle numbers M by describing the system as an ensemble of an N and an N+1 particle system (with N{<=}M{<=}N+1). For each fixed particle number, M, the total energy is minimized with respect to the natural orbitals and their occupation numbers. This leads to the total energy as a function of M. The derivative of this function with respect to the particle number has a discontinuity at integer particle number which is identical to the gap. In addition, we investigate the necessary and sufficient conditions for the 1- RDM of a system with fractional particle number to be N-representable. Numerical results are presented for alkali atoms, small molecules, and periodic systems. Another problem within DFT is the description of non-relativistic many-electron systems in the presence of magnetic fields. It requires the paramagnetic current density and the spin magnetization to be used as basic variables besides the electron density. However, electron-gas-based functionals of current-spin-density-functional Theory (CSDFT) exhibit derivative discontinuities as a function of the magnetic field whenever a new Landau level is occupied, which makes them difficult to use in practice. Since the appearance of Landau levels is, intrinsically, an orbital effect it is appealing to use orbital-dependent functionals. We have developed a CSDFT version of the optimized

  3. All-phosphorus flexible devices with non-collinear electrodes: a first principles study.

    Science.gov (United States)

    Li, Junjun; Ruan, Lufeng; Wu, Zewen; Zhang, Guiling; Wang, Yin

    2018-03-07

    With the continuous expansion of the family of two-dimensional (2D) materials, flexible electronics based on 2D materials have quickly emerged. Theoretically, predicting the transport properties of the flexible devices made up of 2D materials using first principles is of great importance. Using density functional theory combined with the non-equilibrium Green's function formalism, we calculated the transport properties of all-phosphorus flexible devices with non-collinear electrodes, and the results predicted that the device with compressed metallic phosphorene electrodes sandwiching a P-type semiconducting phosphorene shows a better and robust conducting behavior against the bending of the semiconducting region when the angle between the two electrodes is less than 45°, which indicates that this system is very promising for flexible electronics. The calculation of a quantum transport system with non-collinear electrodes demonstrated in this work will provide more interesting information on mesoscopic material systems and related devices.

  4. First-principles data-driven discovery of transition metal oxides for artificial photosynthesis

    Science.gov (United States)

    Yan, Qimin

    We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.

  5. First Principles Modeling and Interpretation of Ionization-Triggered Charge Migration in Molecules

    Science.gov (United States)

    Bruner, Adam; Hernandez, Sam; Mauger, Francois; Abanador, Paul; Gaarde, Mette; Schafer, Ken; Lopata, Ken

    Modeling attosecond coherent charge migration in molecules is important for understanding initial steps of photochemistry and light harvesting processes. Ionization triggered hole migration can be difficult to characterize and interpret as the dynamics can be convoluted with excited states. Here, we introduce a real-time time-dependent density functional theory (RT-TDDFT) approach for modeling such dynamics from first principles. To isolate the specific hole dynamics from excited states, Fourier transform analysis and orbital occupations are used to provide a spatial hole representation in the frequency domain. These techniques are applied to hole transfer across a thiophene dimer as well as core-hole triggered valence motion in nitrosobenzene. This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0012462.

  6. First-principles investigation of Fe-doped MgSiO3-ilmenite

    International Nuclear Information System (INIS)

    Stashans, Arvids; Rivera, Krupskaya; Pinto, Henry P.

    2012-01-01

    First principles density functional theory and generalised gradient approximation (GGA) have been exploited to investigate Fe-doped ilmenite-type MgSiO 3 mineral. Strong electron correlation effects not included in a density-functional formalism are described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach). Microstructure of equilibrium geometries, electronic band structures as well as magnetic properties are computed and discussed in detail. Hartree-Fock methodology is used as an extra tool to study optical properties of the same system. For equilibrium state of the doped mineral we find zigzag-type atomic rearrangements around the Fe impurity. The inclusion of correlation effects leads to an improved description of the electronic properties. In particular, it is discovered that Fe incorporation produces local energy levels within the band-gap of the material. Using ΔSCF method optical absorption energies are found to be equal to 2.2 and 2.6 eV leading to light absorption at longer wavelengths compared to the undoped MgSiO 3 . Our results provide evidence on the occurrence of local magnetic moment in the region surrounding iron dopant. According to the outcomes, the Fe⇒Mg reaction can be described as substitutionally labile with Fe 2+ complex being found in the high-spin state at low pressure MgSiO 3 -ilmenite conditions.

  7. Oxygen vacancy effects in HfO2-based resistive switching memory: First principle study

    Directory of Open Access Journals (Sweden)

    Yuehua Dai

    2016-08-01

    Full Text Available The work investigated the shape and orientation of oxygen vacancy clusters in HfO2-base resistive random access memory (ReRAM by using the first-principle method based on the density functional theory. Firstly, the formation energy of different local Vo clusters was calculated in four established orientation systems. Then, the optimized orientation and charger conductor shape were identified by comparing the isosurface plots of partial charge density, formation energy, and the highest isosurface value of oxygen vacancy. The calculated results revealed that the [010] orientation was the optimal migration path of Vo, and the shape of system D4 was the best charge conductor in HfO2, which effectively influenced the SET voltage, formation voltage and the ON/OFF ratio of the device. Afterwards, the PDOS of Hf near Vo and total density of states of the system D4_010 were obtained, revealing the composition of charge conductor was oxygen vacancy instead of metal Hf. Furthermore, the migration barriers of the Vo hopping between neighboring unit cells were calculated along four different orientations. The motion was proved along [010] orientation. The optimal circulation path for Vo migration in the HfO2 super-cell was obtained.

  8. First-principles calculations, experimental study, and thermodynamic modeling of the Al-Co-Cr system.

    Directory of Open Access Journals (Sweden)

    Xuan L Liu

    Full Text Available The phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system are investigated using first-principles calculations based on density functional theory (DFT and phase-equilibria experiments that led to X-ray diffraction (XRD and electron probe micro-analysis (EPMA measurements. A thermodynamic description is developed by means of the calculations of phase diagrams (CALPHAD method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the bcc-A2, B2, fcc-γ, and tetragonal-σ phases in the temperature range of 1173 to 1623 K. Liquid, bcc-A2 and fcc-γ phases are modeled using substitutional solution descriptions. First-principles special quasirandom structures (SQS calculations predict a large bcc-A2 (disordered/B2 (ordered miscibility gap, in agreement with experiments. A partitioning model is then used for the A2/B2 phase to effectively describe the order-disorder transitions. The critically assessed thermodynamic description describes all phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings.

  9. Temperature-dependent stability of stacking faults in Al, Cu and Ni: first-principles analysis.

    Science.gov (United States)

    Bhogra, Meha; Ramamurty, U; Waghmare, Umesh V

    2014-09-24

    We present comparative analysis of microscopic mechanisms relevant to plastic deformation of the face-centered cubic (FCC) metals Al, Cu, and Ni, through determination of the temperature-dependent free energies of intrinsic and unstable stacking faults along [1 1̄ 0] and [1 2̄ 1] on the (1 1 1) plane using first-principles density-functional-theory-based calculations. We show that vibrational contribution results in significant decrease in the free energy of barriers and intrinsic stacking faults (ISFs) of Al, Cu, and Ni with temperature, confirming an important role of thermal fluctuations in the stability of stacking faults (SFs) and deformation at elevated temperatures. In contrast to Al and Ni, the vibrational spectrum of the unstable stacking fault (USF[1 2̄ 1]) in Cu reveals structural instabilities, indicating that the energy barrier (γusf) along the (1 1 1)[1 2̄ 1] slip system in Cu, determined by typical first-principles calculations, is an overestimate, and its commonly used interpretation as the energy release rate needed for dislocation nucleation, as proposed by Rice (1992 J. Mech. Phys. Solids 40 239), should be taken with caution.

  10. First-principles studies of di-arsenic interstitial and its implications for arsenic-interstitial diffusion in crystalline silicon

    International Nuclear Information System (INIS)

    Kim, Yonghyun; Kirichenko, Taras A.; Kong, Ning; Larson, Larry; Banerjee, Sanjay K.

    2007-01-01

    We propose new structural configurations and novel diffusion mechanisms for neutral di-arsenic interstitial (As 2 I 2 ) in silicon with a first-principle density functional theory simulation within the generalized gradient approximation. With an assumption of excess silicon interstitials and high arsenic concentrations, neutral As 2 I 2 is expected to be favorable and mobile with low-migration barrier. Moreover, because the diffusion barrier of arsenic interstitial pairs (AsI) is very low ( 2 I 2 can be easily formed and likely intermediate stage of larger arsenic interstitial clusters

  11. First-principles study on electronic, optic, elastic, dynamic and thermodynamic properties of RbH compound

    Directory of Open Access Journals (Sweden)

    Gulebaglan Sinem Erden

    2015-01-01

    Full Text Available We performed first-principles calculations to obtain the electronic, optical, elastic, lattice-dynamical and thermodynamic properties of RbH compound with rock salt structure. The ground-state properties, i.e., the lattice constant and the band gap were investigated using a plane wave pseudopotential method within density functional theory. The calculated lattice constant, bulk modulus, energy band gap and elastic constants are reported and compared with previous theoretical and experimental results. Our calculated results and the previous results which are obtained from literature are in a good agreement. Moreover, real and imaginary parts of complex dielectric function, reflectivity spectrum, absorption, extinction coefficient and loss function as a function of photon energy and refractive index with respect to photon wavelength were calculated. In addition, temperature dependent thermodynamic properties such as Helmholtz free energy, internal energy, entropy and specific heat have been studied.

  12. First principles simulation on the K0.8Fe2Se2 high-temperature structural superconductor

    International Nuclear Information System (INIS)

    Guo, Rui; Yang, Shizhong; Khosravi, Ebrahim; Zhao, Guang-Lin; Bagayoko, Diola

    2013-01-01

    Highlights: • The superconductor K 0.8 Fe 2 Se 2 super cell size, shape, and atomic positions are fully optimized using first principles density functional theory method. • Each K atom donates 0.8 |e| with K vacancies in the supercell, each Fe atom donates 0.4 |e|, while each Se atom gains 0.7 |e| ∼ 0.8 |e|. • Fe atoms show magnetic moment fluctuation and possible strong spin-orbital coupling. -- Abstract: Since the synthesis of the first ones in 2008, iron-based high temperature superconductors have been the subject of many studies. This great interest is partly due to their higher, upper magnetic field, smaller Fermi surface around the Γ point, and a larger coherence length. This work is focused on A x Fe 2 Se 2 structural superconductor (FeSe, 11 hierarchy; A = K, Cs) as recently observed. ARPES data show novel, electronic structure and a hole-free Fermi surface which is different from previously observed Fermi surface images. We use ab initio density functional theory method to simulate the electronic structure of the novel superconductor A x Fe 2 Se 2 . We compare this electronic structure with those of other Fe-based superconductors

  13. Ensemble Assimilation Using Three First-Principles Thermospheric Models as a Tool for 72-hour Density and Satellite Drag Forecasts

    Science.gov (United States)

    Hunton, D.; Pilinski, M.; Crowley, G.; Azeem, I.; Fuller-Rowell, T. J.; Matsuo, T.; Fedrizzi, M.; Solomon, S. C.; Qian, L.; Thayer, J. P.; Codrescu, M.

    2014-12-01

    Much as aircraft are affected by the prevailing winds and weather conditions in which they fly, satellites are affected by variability in the density and motion of the near earth space environment. Drastic changes in the neutral density of the thermosphere, caused by geomagnetic storms or other phenomena, result in perturbations of satellite motions through drag on the satellite surfaces. This can lead to difficulties in locating important satellites, temporarily losing track of satellites, and errors when predicting collisions in space. As the population of satellites in Earth orbit grows, higher space-weather prediction accuracy is required for critical missions, such as accurate catalog maintenance, collision avoidance for manned and unmanned space flight, reentry prediction, satellite lifetime prediction, defining on-board fuel requirements, and satellite attitude dynamics. We describe ongoing work to build a comprehensive nowcast and forecast system for neutral density, winds, temperature, composition, and satellite drag. This modeling tool will be called the Atmospheric Density Assimilation Model (ADAM). It will be based on three state-of-the-art coupled models of the thermosphere-ionosphere running in real-time, using assimilative techniques to produce a thermospheric nowcast. It will also produce, in realtime, 72-hour predictions of the global thermosphere-ionosphere system using the nowcast as the initial condition. We will review the requirements for the ADAM system, the underlying full-physics models, the plethora of input options available to drive the models, a feasibility study showing the performance of first-principles models as it pertains to satellite-drag operational needs, and review challenges in designing an assimilative space-weather prediction model. The performance of the ensemble assimilative model is expected to exceed the performance of current empirical and assimilative density models.

  14. Gentlest ascent dynamics for calculating first excited state and exploring energy landscape of Kohn-Sham density functionals.

    Science.gov (United States)

    Li, Chen; Lu, Jianfeng; Yang, Weitao

    2015-12-14

    We develop the gentlest ascent dynamics for Kohn-Sham density functional theory to search for the index-1 saddle points on the energy landscape of the Kohn-Sham density functionals. These stationary solutions correspond to excited states in the ground state functionals. As shown by various examples, the first excited states of many chemical systems are given by these index-1 saddle points. Our novel approach provides an alternative, more robust way to obtain these excited states, compared with the widely used ΔSCF approach. The method can be easily generalized to target higher index saddle points. Our results also reveal the physical interest and relevance of studying the Kohn-Sham energy landscape.

  15. Structural, Mechanical and Thermodynamic Properties under Pressure Effect of Rubidium Telluride: First Principle Calculations

    Directory of Open Access Journals (Sweden)

    Bidai K.

    2017-06-01

    Full Text Available First-principles density functional theory calculations have been performed to investigate the structural, elastic and thermodynamic properties of rubidium telluride in cubic anti-fluorite (anti-CaF2-type structure. The calculated ground-state properties of Rb2Te compound such as equilibrium lattice parameter and bulk moduli are investigated by generalized gradient approximation (GGA-PBE that are based on the optimization of total energy. The elastic constants, Young’s and shear modulus, Poisson ratio, have also been calculated. Our results are in reasonable agreement with the available theoretical and experimental data. The pressure dependence of elastic constant and thermodynamic quantities under high pressure are also calculated and discussed.

  16. First-principles prediction of shape memory behavior and ferrimagnetism in Mn2NiSn

    International Nuclear Information System (INIS)

    Paul, Souvik; Ghosh, Subhradip

    2011-01-01

    Using first-principles density functional theory, we show that, in Mn 2 NiSn, an energy lowering phase transition from the cubic to tetragonal phase occurs which indicates a martensitic phase transition. This structural phase transition is nearly volume-conserving, implying that this alloy can exhibit shape memory behavior. The magnetic ground state is a ferrimagnetic one with antiparallel Mn spin moments. The calculated moments with different electronic structure methods in the cubic phase compare well with each other but differ from the experimental values by more than 1 μ B . The reason behind this discrepancy is explored by considering antisite disorder in our calculations, which indicates that the site ordering in this alloy can be quite complex.

  17. Density functional theory for field emission from carbon nano-structures

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhibing, E-mail: stslzb@mail.sysu.edu.cn

    2015-12-15

    Electron field emission is understood as a quantum mechanical many-body problem in which an electronic quasi-particle of the emitter is converted into an electron in vacuum. Fundamental concepts of field emission, such as the field enhancement factor, work-function, edge barrier and emission current density, will be investigated, using carbon nanotubes and graphene as examples. A multi-scale algorithm basing on density functional theory is introduced. We will argue that such a first principle approach is necessary and appropriate for field emission of nano-structures, not only for a more accurate quantitative description, but, more importantly, for deeper insight into field emission. - Highlights: • Applications of DFT to electron field emission of nano-structures are reviewed. • Fundamental concepts of field emission are re-visited with emphasis on the many-body effects. • New insights to field emission of nano-structures are obtained by multi-scale DFT calculations. • It is shown that the exchange–correlation effect on the emission barrier is significant. • Spontaneous symmetry breaking in field emission of CNT has been predicted.

  18. The QTP family of consistent functionals and potentials in Kohn-Sham density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Yifan; Bartlett, Rodney J., E-mail: bartlett@qtp.ufl.edu [Quantum Theory Project and Departments of Chemistry and Physics, University of Florida, Gainesville, Florida 32611 (United States)

    2016-07-21

    This manuscript presents the second, consistent density functional in the QTP (Quantum Theory Project) family, that is, the CAM-QTP(01). It is a new range-separated exchange-correlation functional in which the non-local exchange contribution is 100% at large separation. It follows the same basic principles of this family that the Kohn-Sham eigenvalues of the occupied orbitals approximately equal the vertical ionization energies, which is not fulfilled by most of the traditional density functional methods. This new CAM-QTP(01) functional significantly improves the accuracy of the vertical excitation energies especially for the Rydberg states in the test set. It also reproduces many other properties such as geometries, reaction barrier heights, and atomization energies.

  19. Functional derivative of noninteracting kinetic energy density functional

    International Nuclear Information System (INIS)

    Liu Shubin; Ayers, Paul W.

    2004-01-01

    Proofs from different theoretical frameworks, namely, the Hohenbergh-Kohn theorems, the Kohn-Sham scheme, and the first-order density matrix representation, have been presented in this paper to show that the functional derivative of the noninteracting kinetic energy density functional can uniquely be expressed as the negative of the Kohn-Sham effective potential, arbitrary only to an additive orbital-independent constant. Key points leading to the current result as well as confusion about the quantity in the literature are briefly discussed

  20. Combining Kohn-Sham and orbital-free density-functional theory for Hugoniot calculations to extreme pressures.

    Science.gov (United States)

    Sheppard, Daniel; Kress, Joel D; Crockett, Scott; Collins, Lee A; Desjarlais, Michael P

    2014-12-01

    The shock Hugoniot for lithium 6 deuteride ((6)LiD) was calculated via first principles using Kohn-Sham density-functional theory molecular dynamics (KSMD) for temperatures of 0.5-25 eV. The upper limit of 25 eV represents a practical limit where KSMD is no longer computationally feasible due to the number of electronic bands which are required to be populated. To push the Hugoniot calculations to higher temperatures we make use of orbital-free density-functional theory molecular dynamics (OFMD). Thomas-Fermi-Dirac-based OFMD gives a poor description of the electronic structure at low temperatures so the initial state is not well defined. We propose a method of bootstrapping the Hugoniot from OFMD to the Hugoniot from KSMD between 10 and 20 eV, where the two methods are in agreement. The combination of KSMD and OFMD allows construction of a first-principles Hugoniot from the initial state to 1000 eV. Theoretical shock-compression results are in good agreement with available experimental data and exhibit the appropriate high-temperature limits. We show that a unified KSMD-OFMD Hugoniot can be used to assess the quality of the existing equation-of-state (EOS) models and inform better EOS models based on justifiable physics.

  1. First-principles calculations of novel materials

    Science.gov (United States)

    Sun, Jifeng

    Computational material simulation is becoming more and more important as a branch of material science. Depending on the scale of the systems, there are many simulation methods, i.e. first-principles calculation (or ab-initio), molecular dynamics, mesoscale methods and continuum methods. Among them, first-principles calculation, which involves density functional theory (DFT) and based on quantum mechanics, has become to be a reliable tool in condensed matter physics. DFT is a single-electron approximation in solving the many-body problems. Intrinsically speaking, both DFT and ab-initio belong to the first-principles calculation since the theoretical background of ab-initio is Hartree-Fock (HF) approximation and both are aimed at solving the Schrodinger equation of the many-body system using the self-consistent field (SCF) method and calculating the ground state properties. The difference is that DFT introduces parameters either from experiments or from other molecular dynamic (MD) calculations to approximate the expressions of the exchange-correlation terms. The exchange term is accurately calculated but the correlation term is neglected in HF. In this dissertation, DFT based first-principles calculations were performed for all the novel materials and interesting materials introduced. Specifically, the DFT theory together with the rationale behind related properties (e.g. electronic, optical, defect, thermoelectric, magnetic) are introduced in Chapter 2. Starting from Chapter 3 to Chapter 5, several representative materials were studied. In particular, a new semiconducting oxytelluride, Ba2TeO is studied in Chapter 3. Our calculations indicate a direct semiconducting character with a band gap value of 2.43 eV, which agrees well with the optical experiment (˜ 2.93 eV). Moreover, the optical and defects properties of Ba2TeO are also systematically investigated with a view to understanding its potential as an optoelectronic or transparent conducting material. We find

  2. Wobbled electronic properties of lithium clusters: Deterministic approach through first principles

    Science.gov (United States)

    Kushwaha, Anoop Kumar; Nayak, Saroj Kumar

    2018-03-01

    The innate tendency to form dendritic growth promoted through cluster formation leading to the failure of a Li-ion battery system have drawn significant attention of the researchers towards the effective destabilization of the cluster growth through selective implementation of electrolytic media such as acetonitrile (MeCN). In the present work, using first principles density functional theory and continuum dielectric model, we have investigated the origin of oscillatory nature of binding energy per atom of Lin (n ≤ 8) under the influence of MeCN. In the gas phase, we found that static mean polarizability is strongly correlated with binding energy and shows oscillatory nature with cluster size due to the open shell of Lin cluster. However, in acetonitrile medium, the binding energy has been correlated with electrostatic Lin -MeCN interaction and it has been found that both of them possess wobbled behavior characterized by the cluster size.

  3. Electrical properties of improper ferroelectrics from first principles

    Science.gov (United States)

    Stengel, Massimiliano; Fennie, Craig J.; Ghosez, Philippe

    2012-09-01

    We study the interplay of structural and polar distortions in hexagonal YMnO3 and short-period PbTiO3/SrTiO3 (PTO/STO) superlattices by means of first-principles calculations at constrained electric displacement field D. We find that in YMnO3 the tilts of the oxygen polyhedra produce a robustly polar ground state, which persists at any choice of the electrical boundary conditions. Conversely, in PTO/STO the antiferrodistortive instabilities alone do not break inversion symmetry, and open-circuit boundary conditions restore a nonpolar state. We suggest that this qualitative difference naturally provides a route to rationalizing the concept of “improper ferroelectricity” from the point of view of first-principles theory. We discuss the implications of our arguments for the design of novel multiferroic materials with enhanced functionalities and for the symmetry analysis of the phase transitions.

  4. Absorption of CO2 on Carbon-based Sensors: First-Principle Analysis

    Science.gov (United States)

    Tit, Nacir; Elezzi, Mohammed; Abdullah, Hasan; Bahlouli, Hocine; Yamani, Zain

    We present first-principle investigation of the adsorption properties of CO and CO2 molecules on both graphene and carbon nano-tubes (CNTs) in presence of metal catalysis, mainly iron (Fe). The relaxations were carried out using the self-consistent-charge density-functional tight-binding (SCC-DFTB) code in neglect of heat effects. The results show the following: (1) Defected graphene is found to have high sensitivity and high selectivity towards chemisorption of CO molecules and weak physisorption with CO2 molecules. (2) In case of CNTs, the iron ``Fe'' catalyst plays an essential role in capturing CO2 molecules. The Fe ad-atoms on the surface of CNT introduce huge density of states at Fermi level, but the capture of CO2 molecules would reduce that density and consequently reduce conductivity and increase sensitivity. Concerning the selectivity, we have studied the sensitivity versus various gas molecules (such as: O2, N2, H2, H2O, and CO). Furthermore, to assess the effect of catalysis on sensitivity, we have studied the sensitivity of other metal catalysts (such as: Ni, Co, Ti, and Sc). We found that CNT-Fe is highly sensitive and selective towards detection of CO and CO2 molecules. CNT being conductive or semiconducting does not matter much on the adsorption properties.

  5. Improving density functional tight binding predictions of free energy surfaces for peptide condensation reactions in solution

    Science.gov (United States)

    Kroonblawd, Matthew; Goldman, Nir

    First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for chemistry that is fast relative to DFT simulation times (Contract DE-AC52-07NA27344.

  6. Improving Density Functional Tight Binding Predictions of Free Energy Surfaces for Slow Chemical Reactions in Solution

    Science.gov (United States)

    Kroonblawd, Matthew; Goldman, Nir

    2017-06-01

    First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for reactions that are fast relative to DFT simulation times (Contract DE-AC52-07NA27344.

  7. Density functional theory

    International Nuclear Information System (INIS)

    Freyss, M.

    2015-01-01

    This chapter gives an introduction to first-principles electronic structure calculations based on the density functional theory (DFT). Electronic structure calculations have a crucial importance in the multi-scale modelling scheme of materials: not only do they enable one to accurately determine physical and chemical properties of materials, they also provide data for the adjustment of parameters (or potentials) in higher-scale methods such as classical molecular dynamics, kinetic Monte Carlo, cluster dynamics, etc. Most of the properties of a solid depend on the behaviour of its electrons, and in order to model or predict them it is necessary to have an accurate method to compute the electronic structure. DFT is based on quantum theory and does not make use of any adjustable or empirical parameter: the only input data are the atomic number of the constituent atoms and some initial structural information. The complicated many-body problem of interacting electrons is replaced by an equivalent single electron problem, in which each electron is moving in an effective potential. DFT has been successfully applied to the determination of structural or dynamical properties (lattice structure, charge density, magnetisation, phonon spectra, etc.) of a wide variety of solids. Its efficiency was acknowledged by the attribution of the Nobel Prize in Chemistry in 1998 to one of its authors, Walter Kohn. A particular attention is given in this chapter to the ability of DFT to model the physical properties of nuclear materials such as actinide compounds. The specificities of the 5f electrons of actinides will be presented, i.e., their more or less high degree of localisation around the nuclei and correlations. The limitations of the DFT to treat the strong 5f correlations are one of the main issues for the DFT modelling of nuclear fuels. Various methods that exist to better treat strongly correlated materials will finally be presented. (author)

  8. Electronic and optical properties of RESn{sub 3} (RE=Pr & Nd) intermetallics: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pagare, G., E-mail: gita-pagare@yahoo.co.in [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Abraham, Jisha A. [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Department of Physics, National Defence Academy, Pune-411023 (India); Sanyal, S. P. [Department of Physics, Barkatullah University, Bhopal-462026 (India)

    2015-06-24

    A theoretical study of structural, electronic and optical properties of RESn{sub 3} (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linear optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.

  9. Fe magnetic moment formation and exchange interaction in Fe{sub 2}P: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, X.B., E-mail: liuxubo@uta.edu [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Ping Liu, J.; Zhang, Qiming [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Altounian, Z. [Center for the Physics of Materials and Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8 (Canada)

    2013-03-15

    Electronic structure and magnetic properties of Fe{sub 2}P have been studied by a first-principles density functional theory calculation. The ground state is ferromagnetic and the calculated magnetic moments for Fe{sub 1} (3f) and Fe{sub 2} (3g) are 0.83 and 2.30μ{sub B}, respectively. The nearest neighbor inter-site magnetic exchange coupling parameter at the Fe{sub 1} layer (0.02 mRy) is much smaller than that at the Fe{sub 2} layer (1.29 mRy). The Fe moment at the 3f site is metastable and sensitive to the inter-site exchange interaction with its magnetic neighbors, which is responsible for the first order magnetic transition and large magneto-caloric effect around T{sub C}.

  10. First principles investigation of structural, electronic, elastic and thermal properties of rare-earth-doped titanate Ln2TiO5

    Directory of Open Access Journals (Sweden)

    Hui Niu

    2012-09-01

    Full Text Available Systematic first-principles calculations based on density functional theory were performed on a wide range of Ln2TiO5 compositions (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Y in order to investigate their structural, elastic, electronic, and thermal properties. At low temperature, these compounds crystallize in orthorhombic structures with a Pnma symmetry, and the calculated equilibrium structural parameters agree well with experimental results. A complete set of elastic parameters including elastic constants, Hill's bulk moduli, Young's moduli, shear moduli and Poisson's ratio were calculated. All Ln2TiO5 are ductile in nature. Analysis of densities of states and charge densities and electron localization functions suggests that the oxide bonds are highly ionic with some degree of covalency in the Ti-O bonds. Thermal properties including the mean sound velocity, Debye temperature, and minimum thermal conductivity were obtained from the elastic constants.

  11. First-principles study of the structure properties of Al(111)/6H-SiC(0001) interfaces

    Science.gov (United States)

    Wu, Qingjie; Xie, Jingpei; Wang, Changqing; Li, Liben; Wang, Aiqin; Mao, Aixia

    2018-04-01

    This paper presents a systematic study on the energetic and electronic structure of the Al(111)/6H-SiC(0001) interfaces by using first-principles calculation with density functional theory (DFT). There are all three situations for no-vacuum layer of Al/SiC superlattics, and two cases of C-terminated and Si-terminated interfaces are compared and analyzed. Through the density of states analysis, the initial information of interface combination is obtained. Then the supercells are stretched vertically along the z-axis, and the fracture of the interface is obtained, and it is pointed out that C-terminated SiC and Al interfaces have a better binding property. And, the fracture positions of C-terminated and Si-terminated interfaces are different in the process of stretching. Then, the distance variation in the process of stretching, the charge density differences, and the distribution of the electrons near the interface are analyzed. Al these work makes the specific reasons for the interface fracture are obtained at last.

  12. Tailoring graphene magnetism by zigzag triangular holes: A first-principles thermodynamics study

    Directory of Open Access Journals (Sweden)

    Muhammad Ejaz Khan

    2016-03-01

    Full Text Available We discuss the thermodynamic stability and magnetic property of zigzag triangular holes (ZTHs in graphene based on the results of first-principles density functional theory calculations. We find that ZTHs with hydrogen-passivated edges in mixed sp2/sp3 configurations (z211 could be readily available at experimental thermodynamic conditions, but ZTHs with 100% sp2 hydrogen-passivation (z1 could be limitedly available at high temperature and ultra-high vacuum conditions. Graphene magnetization near the ZTHs strongly depends on the type and the size of the triangles. While metallic z1 ZTHs exhibit characteristic edge magnetism due to the same-sublattice engineering, semiconducting z211 ZTHs do show characteristic corner magnetism when the size is small <2 nm. Our findings could be useful for experimentally tailoring metal-free carbon magnetism by simply fabricating triangular holes in graphene.

  13. Ab initio derivation of model energy density functionals

    International Nuclear Information System (INIS)

    Dobaczewski, Jacek

    2016-01-01

    I propose a simple and manageable method that allows for deriving coupling constants of model energy density functionals (EDFs) directly from ab initio calculations performed for finite fermion systems. A proof-of-principle application allows for linking properties of finite nuclei, determined by using the nuclear nonlocal Gogny functional, to the coupling constants of the quasilocal Skyrme functional. The method does not rely on properties of infinite fermion systems but on the ab initio calculations in finite systems. It also allows for quantifying merits of different model EDFs in describing the ab initio results. (letter)

  14. First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3

    Science.gov (United States)

    Mubarak, A. A.; Al-Omari, Saleh

    2015-05-01

    We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF3 and RbNiF3. The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF3 compound has a half-metallic behavior while the RbNiF3 compound has a semiconductor behavior with indirect (M-Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra.

  15. Spin resolved electronic transport through N@C20 fullerene molecule between Au electrodes: A first principles study

    Science.gov (United States)

    Caliskan, Serkan

    2018-05-01

    Using first principles study, through Density Functional Theory combined with Non Equilibrium Green's Function Formalism, electronic properties of endohedral N@C20 fullerene molecule joining Au electrodes (Au-N@C20) was addressed in the presence of spin property. The electronic transport behavior across the Au-N@C20 molecular junction was investigated by spin resolved transmission, density of states, molecular orbitals, differential conductance and current-voltage (I-V) characteristics. Spin asymmetric variation was clearly observed in the results due to single N atom encapsulated in the C20 fullerene cage, where the N atom played an essential role in the electronic behavior of Au-N@C20. This N@C20 based molecular bridge, exhibiting a spin dependent I-V variation, revealed a metallic behavior within the bias range from -1 V to 1 V. The induced magnetic moment, spin polarization and other relevant quantities associated with the spin resolved transport were elucidated.

  16. First-principles study of direct and narrow band gap semiconducting β-CuGaO2

    International Nuclear Information System (INIS)

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-01-01

    Semiconducting oxides have attracted much attention due to their great stability in air or water and the abundance of oxygen. Recent success in synthesizing a metastable phase of CuGaO 2 with direct narrow band gap opens up new applications of semiconducting oxides as absorber layer for photovoltaics. Using first-principles density functional theory calculations, we investigate the thermodynamic and mechanical stabilities as well as the structural and electronic properties of the β-CuGaO 2 phase. Our calculations show that the β-CuGaO 2 structure is dynamically and mechanically stable. The energy band gap is confirmed to be direct at the Γ point of Brillouin zone. The optical absorption occurs right at the band gap edge and the density of states near the valance band maximum is large, inducing an intense absorption of light as observed in experiment. (paper)

  17. Defects in boron carbide: First-principles calculations and CALPHAD modeling

    International Nuclear Information System (INIS)

    Saengdeejing, Arkapol; Saal, James E.; Manga, Venkateswara Rao; Liu Zikui

    2012-01-01

    The energetics of defects in B 4+x C boron carbide and β-boron are studied through first-principles calculations, the supercell phonon approach and the Debye–Grüneisen model. It is found that suitable sublattice models for β-boron and B 4+x C are B 101 (B,C) 4 and B 11 (B,C) (B,C,Va) (B,Va) (B,C,Va), respectively. The thermodynamic properties of B 4+x C, β-boron, liquid and graphite are modeled using the CALPHAD approach based on the thermochemical data from first-principles calculations and experimental phase equilibrium data in the literature. The concentrations of various defects are then predicted as a function of carbon composition and temperature.

  18. Magnetism, microstructure and First Principles calculations of atomized and annealed Ni3Al

    International Nuclear Information System (INIS)

    García-Escorial, A.; Crespo, P.; Hernando, A.; Lieblich, M.; Marín, P.; Velasco, V.; Ynduráin, F.

    2014-01-01

    Highlights: • The microstructure and order of as-atomized Ni 3 Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni 3 Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni 3 Al, L1 2 , phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position

  19. Rydberg energies using excited state density functional theory

    International Nuclear Information System (INIS)

    Cheng, C.-L.; Wu Qin; Van Voorhis, Troy

    2008-01-01

    We utilize excited state density functional theory (eDFT) to study Rydberg states in atoms. We show both analytically and numerically that semilocal functionals can give quite reasonable Rydberg energies from eDFT, even in cases where time dependent density functional theory (TDDFT) fails catastrophically. We trace these findings to the fact that in eDFT the Kohn-Sham potential for each state is computed using the appropriate excited state density. Unlike the ground state potential, which typically falls off exponentially, the sequence of excited state potentials has a component that falls off polynomially with distance, leading to a Rydberg-type series. We also address the rigorous basis of eDFT for these systems. Perdew and Levy have shown using the constrained search formalism that every stationary density corresponds, in principle, to an exact stationary state of the full many-body Hamiltonian. In the present context, this means that the excited state DFT solutions are rigorous as long as they deliver the minimum noninteracting kinetic energy for the given density. We use optimized effective potential techniques to show that, in some cases, the eDFT Rydberg solutions appear to deliver the minimum kinetic energy because the associated density is not pure state v-representable. We thus find that eDFT plays a complementary role to constrained DFT: The former works only if the excited state density is not the ground state of some potential while the latter applies only when the density is a ground state density.

  20. First-principles study on band structures and electrical transports of doped-SnTe

    Directory of Open Access Journals (Sweden)

    Xiao Dong

    2016-06-01

    Full Text Available Tin telluride is a thermoelectric material that enables the conversion of thermal energy to electricity. SnTe demonstrates a great potential for large-scale applications due to its lead-free nature and the similar crystal structure to PbTe. In this paper, the effect of dopants (i.e., Mg, Ca, Sr, Ba, Eu, Yb, Zn, Cd, Hg, and In on the band structures and electrical transport properties of SnTe was investigated based on the first-principles density functional theory including spin–orbit coupling. The results show that Zn and Cd have a dominant effect of band convergence, leading to power factor enhancement. Indium induces obvious resonant states, while Hg-doped SnTe exhibits a different behavior with defect states locating slightly above the Fermi level.

  1. Liquid Water from First Principles: Validation of Different Sampling Approaches

    Energy Technology Data Exchange (ETDEWEB)

    Mundy, C J; Kuo, W; Siepmann, J; McGrath, M J; Vondevondele, J; Sprik, M; Hutter, J; Parrinello, M; Mohamed, F; Krack, M; Chen, B; Klein, M

    2004-05-20

    A series of first principles molecular dynamics and Monte Carlo simulations were carried out for liquid water to assess the validity and reproducibility of different sampling approaches. These simulations include Car-Parrinello molecular dynamics simulations using the program CPMD with different values of the fictitious electron mass in the microcanonical and canonical ensembles, Born-Oppenheimer molecular dynamics using the programs CPMD and CP2K in the microcanonical ensemble, and Metropolis Monte Carlo using CP2K in the canonical ensemble. With the exception of one simulation for 128 water molecules, all other simulations were carried out for systems consisting of 64 molecules. It is found that the structural and thermodynamic properties of these simulations are in excellent agreement with each other as long as adiabatic sampling is maintained in the Car-Parrinello molecular dynamics simulations either by choosing a sufficiently small fictitious mass in the microcanonical ensemble or by Nos{acute e}-Hoover thermostats in the canonical ensemble. Using the Becke-Lee-Yang-Parr exchange and correlation energy functionals and norm-conserving Troullier-Martins or Goedecker-Teter-Hutter pseudopotentials, simulations at a fixed density of 1.0 g/cm{sup 3} and a temperature close to 315 K yield a height of the first peak in the oxygen-oxygen radial distribution function of about 3.0, a classical constant-volume heat capacity of about 70 J K{sup -1} mol{sup -1}, and a self-diffusion constant of about 0.1 Angstroms{sup 2}/ps.

  2. First-principles investigation of Fe-doped MgSiO{sub 3}-ilmenite

    Energy Technology Data Exchange (ETDEWEB)

    Stashans, Arvids, E-mail: arvids@utpl.edu.ec [Grupo de Fisicoquimica de Materiales, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Rivera, Krupskaya [Grupo de Fisicoquimica de Materiales, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Escuela de Geologia y Minas, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Pinto, Henry P. [Interdisciplinary Center for Nanotoxicity, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217-0510 (United States)

    2012-06-15

    First principles density functional theory and generalised gradient approximation (GGA) have been exploited to investigate Fe-doped ilmenite-type MgSiO{sub 3} mineral. Strong electron correlation effects not included in a density-functional formalism are described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach). Microstructure of equilibrium geometries, electronic band structures as well as magnetic properties are computed and discussed in detail. Hartree-Fock methodology is used as an extra tool to study optical properties of the same system. For equilibrium state of the doped mineral we find zigzag-type atomic rearrangements around the Fe impurity. The inclusion of correlation effects leads to an improved description of the electronic properties. In particular, it is discovered that Fe incorporation produces local energy levels within the band-gap of the material. Using {Delta}SCF method optical absorption energies are found to be equal to 2.2 and 2.6 eV leading to light absorption at longer wavelengths compared to the undoped MgSiO{sub 3}. Our results provide evidence on the occurrence of local magnetic moment in the region surrounding iron dopant. According to the outcomes, the Fe Rightwards-Double-Arrow Mg reaction can be described as substitutionally labile with Fe{sup 2+} complex being found in the high-spin state at low pressure MgSiO{sub 3}-ilmenite conditions.

  3. First-principles calculations of impurity diffusion coefficients in dilute Mg alloys using the 8-frequency model

    International Nuclear Information System (INIS)

    Ganeshan, S.; Hector, L.G.; Liu, Z.-K.

    2011-01-01

    Research highlights: → Implemented the eight frequency model for impurity diffusion in hexagonal metals. → Model inputs were energetics/vibrational properties from first princples. → Predicted diffusion coefficients for Al, Ca, Zn and Sn impurity diffusion in Mg. → Successful prediction of partial correlation factors and jump frequencies. → Good agreement between calculated and experimental results. - Abstract: Diffusion in dilute Mg-X alloys, where X denotes Al, Zn, Sn and Ca impurities, was investigated with first-principles density functional theory in the local density approximation. Impurity diffusion coefficients were computed as a function of temperature using the 8-frequency model which provided the relevant impurity and solvent (Mg) jump frequencies and correlation factors. Minimum energy pathways for impurity diffusion and associated saddle point structures were computed with the climbing image nudged elastic band method. Vibrational properties were obtained with the supercell (direct) method for lattice dynamics. Calculated diffusion coefficients were compared with available experimental data. For diffusion between basal planes, we find D Mg-Ca > D Mg-Zn > D Mg-Sn > D Mg-Al, where D is the diffusion coefficient. For diffusion within a basal plane, the same trend holds except that D Mg-Zn overlaps with D Mg-Al at high temperatures and D Mg-Sn at low temperatures. These trends were explored with charge density contours in selected planes of each Mg-X alloy, the variation of the activation energy for diffusion with the atomic radius of each impurity and the electronic density of states. The theoretical methodology developed herein can be applied to impurity diffusion in other hexagonal materials.

  4. GPU based acceleration of first principles calculation

    International Nuclear Information System (INIS)

    Tomono, H; Tsumuraya, K; Aoki, M; Iitaka, T

    2010-01-01

    We present a Graphics Processing Unit (GPU) accelerated simulations of first principles electronic structure calculations. The FFT, which is the most time-consuming part, is about 10 times accelerated. As the result, the total computation time of a first principles calculation is reduced to 15 percent of that of the CPU.

  5. Theoretical study on the first kind of density wave instabilities

    Energy Technology Data Exchange (ETDEWEB)

    Zuying, Gao; Jincai, Li; Baocheng, Xu; Zuoyi, Zhang; Cheng, Gao [Institute of Nuclear Energy and Technology, Tsingua Univ., Beijing (China)

    1997-09-01

    The present paper summarizes the theoretical studies carried out by INET (Institute of Nuclear Energy Technology) of Tsinghua University on the first kind of density wave instabilities (DWIs) of natural circulation systems. The analysis methods of DWI and mathematical models of drift flux are presented. Based on the general excess entropy production criterion of non-equilibrium thermodynamics, an energy principle of DWI is established. (author). 10 refs, 16 figs.

  6. First-principles calculation on oxygen ion migration in alkaline-earth doped La2GeO5

    International Nuclear Information System (INIS)

    Thuy Linh, Tran Phan; Sakaue, Mamoru; Aspera, Susan Meñez; Alaydrus, Musa; Wungu, Triati Dewi Kencana; Hoang Linh, Nguyen; Kasai, Hideaki; Mohri, Takahiro; Ishihara, Tatsumi

    2014-01-01

    By using first-principles calculations based on the density functional theory, we investigated the doping effects of alkaline-earth metals (Ba, Sr and Ca) in monoclinic lanthanum germanate La 2 GeO 5 on its oxygen ion conduction. Although the lattice parameters of the doped systems changed due to the ionic radii mismatch, the crystal structures remained monoclinic. The contribution of each atomic orbital to electronic densities of states was evaluated from the partial densities of states and partial charge densities. It was confirmed that the materials behaved as ionic crystals comprising of cations of La and dopants and anions of oxygen and covalently formed GeO 4 . The doping effect on the activation barrier for oxygen hopping to the most stable oxygen vacancy site was investigated by the climbing-image nudged elastic band method. By tracing the charge density change during the hopping, it was confirmed that the oxygen motion is governed by covalent interactions. The obtained activation barriers showed excellent quantitative agreements with an experiment for the Ca- and Sr-doped systems in low temperatures as well as the qualitative trend, including the Ba-doped system. (paper)

  7. A first principle study for the comparison of phonon dispersion of armchair carbon and silicon nanotubes

    International Nuclear Information System (INIS)

    Chandel, Surjeet Kumar; Kumar, Arun; Bharti, Ankush; Sharma, Raman

    2015-01-01

    Using first principles density functional theoretical calculations, the present paper reports a systematic study of phonon dispersion curves in pristine carbon (CNT) and silicon nanotubes (SiNT) having chirality (6,6) in the armchair configuration. Some of the phonon modes are found to have negative frequencies which leads to instability of the systems under study. The number of phonon branches has been found to be thrice as much as the number of atoms. The frequency of the higher optical bands varies from 1690 to 1957 cm −1 for CNT(6,6) while it is 596 to 658 cm −1 for SiNT

  8. Generating Tunable Magnetism in AlN Nanoribbons Using Anion/Cation Vacancies:a First-Principles Prediction

    Science.gov (United States)

    Chegeni, Mahdieh; Beiranvand, Razieh; Valedbagi, Shahoo

    2017-04-01

    Using first-principles approach, we theoretically study the effect of anion/cation vacancies on structural and electro-magnetic properties of zigzag AlN nanoribbons (ZAlNNRs). Calculations were performed using a full spin-polarized method within the density functional theory (DFT). Our findings shed light on how the edge states combined with vacancy engineering can affect electro-magnetic properties of ZAlNNRs. We found that depending on the nature and number of vacancies, ZAlNNRs can design as half-metal or semiconductor. Our results reveal a significant amount of spin magnetic moment for ZAlNNR with Al vacancies (VAl). These results may open new applications of AlN nano-materials in spintronics.

  9. Implication of volume changes in uranium oxides: A density functional study

    International Nuclear Information System (INIS)

    Szpunar, B.; Szpunar, J.A.; Milman, V.; Goldberg, A.

    2013-01-01

    In severe nuclear accident scenarios (in air environments and high temperatures) UO 2 fuel pellets oxidise to produce uranium oxides with higher oxygen content, e.g., U 4 O 9 or U 3 O 8 . As a first step in investigating the microstructural changes following UO 2 oxidation to hexagonal high temperature phase of U 3 O 8 , density functional quantum mechanical calculations of the structure, elastic properties and electronic structure of U 3 O 8 have been performed. The calculated properties of hexagonal phase of U 3 O 8 are compared to those of the orthorhombic pseudo-hexagonal phase which is stable at room temperature. The total energy technique based on the local density approximation plus Hubbard U as implemented in the CASTEP code is used to investigate changes in the lattice constants. The first-principles calculations predict a 35-42% increase in volume per uranium atom as a result of the transformation from UO 2 to U 3 O 8 , in agreement with experimental data. The implications of this prediction on the linear expansion and fragmentation of fuel are discussed. (authors)

  10. First principles and Debye model study of the thermodynamic, electronic and optical properties of MgO under high-temperature and pressure

    Science.gov (United States)

    Miao, Yurun; Li, Huayang; Wang, Hongjuan; He, Kaihua; Wang, Qingbo

    2018-02-01

    First principles and quasi-harmonic Debye model have been used to study the thermodynamic properties, enthalpies, electronic and optical properties of MgO up to the core-mantle boundary (CMB) condition (137 GPa and 3700 K). Thermodynamic properties calculation includes thermal expansion coefficient and capacity, which have been studied up to the CMB pressure (137 GPa) and temperature (3700 K) by the Debye model with generalized gradient approximation (GGA) and local-density approximation (LDA). First principles with hybrid functional method (PBE0) has been used to calculate the electronic and optical properties under pressure up to 137 GPa and 0 K. Our results show the Debye model with LDA and first principles with PBE0 can provide accurate thermodynamic properties, enthalpies, electronic and optical properties. Calculated enthalpies show that MgO keep NaCl (B1) structure up to 137 GPa. And MgO is a direct bandgap insulator with a 7.23 eV calculated bandgap. The bandgap increased with increasing pressure, which will induce a blue shift of optical properties. We also calculated the density of states (DOS) and discussed the relation between DOS and band, optical properties. Equations were used to fit the relations between pressure and bandgaps, absorption coefficient (α(ω)) of MgO. The equations can be used to evaluate pressure after careful calibration. Our calculations can not only be used to identify some geological processes, but also offer a reference to the applications of MgO in the future.

  11. A first-principles study of the electronic structure of the sulvanite compounds

    Energy Technology Data Exchange (ETDEWEB)

    Osorio-Guillen, J.M., E-mail: jorge.osorio@fisica.udea.edu.co [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia); Espinosa-Garcia, W.F. [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia)

    2012-03-15

    We have investigated by means of first-principles total energy calculations the electronic structure of the sulvanite compounds: Cu{sub 3}VS{sub 4}, Cu{sub 3}NbS{sub 4} and Cu{sub 3}TaS{sub 4}; the later is a possible candidate as a p-type transparent conductor with potential applications in solar cells and electrochromic devices. The calculated electronic structure shows that these compounds are indirect band gap semiconductors, with the valence band maximum located at the R-point and the conduction band minimum located at the X-point. The character of the valence band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the d-states of the group five elements. From the calculated charge density and electron localisation function we can conclude that the sulvanite compounds are polar covalent semiconductors.

  12. A pair density functional theory utilizing the correlated wave function

    International Nuclear Information System (INIS)

    Higuchi, M; Higuchi, K

    2009-01-01

    We propose a practical scheme for calculating the ground-state pair density (PD) by utilizing the correlated wave function. As the correlated wave function, we adopt a linear combination of the single Slater determinants that are constructed from the solutions of the initial scheme [Higuchi M and Higuchi K 2007 Physica B 387, 117]. The single-particle equation is derived by performing the variational principle within the set of PDs that are constructed from such correlated wave functions. Since the search region of the PD is substantially extended as compared with the initial scheme, it is expected that the present scheme can cover more correlation effects. The single-particle equation is practical, and may be easily applied to actual calculations.

  13. Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations

    International Nuclear Information System (INIS)

    Bennett, Joseph W.; Rabe, Karin M.

    2012-01-01

    In this concept paper, the development of strategies for the integration of first-principles methods with crystallographic database mining for the discovery and design of novel ferroelectric materials is discussed, drawing on the results and experience derived from exploratory investigations on three different systems: (1) the double perovskite Sr(Sb 1/2 Mn 1/2 )O 3 as a candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite MSb 2 O 4 ; and (3) ferroelectric semiconductors with formula M 2 P 2 (S,Se) 6 . A variety of avenues for further research and investigation are suggested, including automated structure type classification, low-symmetry improper ferroelectrics, and high-throughput first-principles searches for additional representatives of structural families with desirable functional properties. - Graphical abstract: Integration of first-principles methods with crystallographic database mining, for the discovery and design of novel ferroelectric materials, could potentially lead to new classes of multifunctional materials. Highlights: ► Integration of first-principles methods and database mining. ► Minor structural families with desirable functional properties. ► Survey of polar entries in the Inorganic Crystal Structural Database.

  14. First-principles investigations on structural, elastic, electronic properties and Debye temperature of orthorhombic Ni3Ta under pressure

    Science.gov (United States)

    Li, Pan; Zhang, Jianxin; Ma, Shiyu; Jin, Huixin; Zhang, Youjian; Zhang, Wenyang

    2018-06-01

    The structural, elastic, electronic properties and Debye temperature of Ni3Ta under different pressures are investigated using the first-principles method based on density functional theory. Our calculated equilibrium lattice parameters at 0 GPa well agree with the experimental and previous theoretical results. The calculated negative formation enthalpies and elastic constants both indicate that Ni3Ta is stable under different pressures. The bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν are calculated by the Voigt-Reuss-Hill method. The bigger ratio of B/G indicates Ni3Ta is ductile and the pressure can improve the ductility of Ni3Ta. In addition, the results of density of states and the charge density difference show that the stability of Ni3Ta is improved by the increasing pressure. The Debye temperature ΘD calculated from elastic modulus increases along with the pressure.

  15. Reduced density matrix functional theory at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Baldsiefen, Tim

    2012-10-15

    Density functional theory (DFT) is highly successful in many fields of research. There are, however, areas in which its performance is rather limited. An important example is the description of thermodynamical variables of a quantum system in thermodynamical equilibrium. Although the finite-temperature version of DFT (FT-DFT) rests on a firm theoretical basis and is only one year younger than its brother, groundstate DFT, it has been successfully applied to only a few problems. Because FT-DFT, like DFT, is in principle exact, these shortcomings can be attributed to the difficulties of deriving valuable functionals for FT-DFT. In this thesis, we are going to present an alternative theoretical description of quantum systems in thermal equilibrium. It is based on the 1-reduced density matrix (1RDM) of the system, rather than on its density and will rather cumbersomly be called finite-temperature reduced density matrix functional theory (FT-RDMFT). Its zero-temperature counterpart (RDMFT) proved to be successful in several fields, formerly difficult to address via DFT. These fields include, for example, the calculation of dissociation energies or the calculation of the fundamental gap, also for Mott insulators. This success is mainly due to the fact that the 1RDM carries more directly accessible ''manybody'' information than the density alone, leading for example to an exact description of the kinetic energy functional. This sparks the hope that a description of thermodynamical systems employing the 1RDM via FT-RDMFT can yield an improvement over FT-DFT. Giving a short review of RDMFT and pointing out difficulties when describing spin-polarized systems initiates our work. We then lay the theoretical framework for FT-RDMFT by proving the required Hohenberg-Kohn-like theorems, investigating and determining the domain of FT-RDMFT functionals and by deriving several properties of the exact functional. Subsequently, we present a perturbative method to

  16. Reduced density matrix functional theory at finite temperature

    International Nuclear Information System (INIS)

    Baldsiefen, Tim

    2012-10-01

    Density functional theory (DFT) is highly successful in many fields of research. There are, however, areas in which its performance is rather limited. An important example is the description of thermodynamical variables of a quantum system in thermodynamical equilibrium. Although the finite-temperature version of DFT (FT-DFT) rests on a firm theoretical basis and is only one year younger than its brother, groundstate DFT, it has been successfully applied to only a few problems. Because FT-DFT, like DFT, is in principle exact, these shortcomings can be attributed to the difficulties of deriving valuable functionals for FT-DFT. In this thesis, we are going to present an alternative theoretical description of quantum systems in thermal equilibrium. It is based on the 1-reduced density matrix (1RDM) of the system, rather than on its density and will rather cumbersomly be called finite-temperature reduced density matrix functional theory (FT-RDMFT). Its zero-temperature counterpart (RDMFT) proved to be successful in several fields, formerly difficult to address via DFT. These fields include, for example, the calculation of dissociation energies or the calculation of the fundamental gap, also for Mott insulators. This success is mainly due to the fact that the 1RDM carries more directly accessible ''manybody'' information than the density alone, leading for example to an exact description of the kinetic energy functional. This sparks the hope that a description of thermodynamical systems employing the 1RDM via FT-RDMFT can yield an improvement over FT-DFT. Giving a short review of RDMFT and pointing out difficulties when describing spin-polarized systems initiates our work. We then lay the theoretical framework for FT-RDMFT by proving the required Hohenberg-Kohn-like theorems, investigating and determining the domain of FT-RDMFT functionals and by deriving several properties of the exact functional. Subsequently, we present a perturbative method to iteratively construct

  17. Spin theory of the density functional: reduced matrices and density functions

    International Nuclear Information System (INIS)

    Pavlov, R.; Delchev, Y.; Pavlova, K.; Maruani, J.

    1993-01-01

    Expressions for the reduced matrices and density functions of N-fermion systems of arbitrary order s (1<=s<=N) are derived within the frame of rigorous spin approach to the density functional theory (DFT). Using the local-scale transformation method and taking into account the particle spin it is shown that the reduced matrices and density functions are functionals of the total one-fermion density. Similar dependence is found for the distribution density of s-particle aggregates. Generalization and applicability of DFT to the case of s-particle ensembles and aggregates is discussed. 14 refs

  18. First principles study the stability and mechanical properties of MC (M = Ti, V, Zr, Nb, Hf and Ta) compounds

    International Nuclear Information System (INIS)

    Liu, YangZhen; Jiang, YeHua; Zhou, Rong; Feng, Jing

    2014-01-01

    Highlights: • The stability and elastic constants of carbides are studied by first principles. • The rules of modulus of MC compounds are discussed by their group. • The hardness of carbides is estimated in this paper at the first time. -- Abstract: The first principles calculations based on density functional theory (DFT) were adopted to investigate the stability, elastic constants, chemical bonding, Debye temperature and hardness of MC (M = Ti, V, Zr, Nb, Hf and Ta) compounds. The cohesive energy and formation enthalpy of these carbides indicate that they are thermodynamically stable structures. The population analysis was used to discuss the chemical bonding of these carbides. The elastic constants and moduli of these compounds were calculated. The results show that the bulk moduli of the carbides of transition metals from the fourth group (TiC, ZrC, HfC) are lower than the fifth group (VC, NbC, TaC). However, the Young’s moduli of the carbides from fourth group are higher than the fifth group. The hardness of compounds was estimated using a semi empirical hardness theory

  19. Machine Learning methods in fitting first-principles total energies for substitutionally disordered solid

    Science.gov (United States)

    Gao, Qin; Yao, Sanxi; Widom, Michael

    2015-03-01

    Density functional theory (DFT) provides an accurate and first-principles description of solid structures and total energies. However, it is highly time-consuming to calculate structures with hundreds of atoms in the unit cell and almost not possible to calculate thousands of atoms. We apply and adapt machine learning algorithms, including compressive sensing, support vector regression and artificial neural networks to fit the DFT total energies of substitutionally disordered boron carbide. The nonparametric kernel method is also included in our models. Our fitted total energy model reproduces the DFT energies with prediction error of around 1 meV/atom. The assumptions of these machine learning models and applications of the fitted total energies will also be discussed. Financial support from McWilliams Fellowship and the ONR-MURI under the Grant No. N00014-11-1-0678 is gratefully acknowledged.

  20. A first-principles study of He, Xe, Kr and O incorporation in thorium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1033 Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1033 Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina)

    2015-05-15

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. Understanding the incorporation of fission products and oxygen is very important to predict the behavior of nuclear fuels. A first approach to this goal is the study of the incorporation energies and stability of these elements in the material. By means of first-principles calculations within the framework of density functional theory, we calculate the incorporation energies of He, Xe, Kr and O atoms in Th and C vacancy sites, in tetrahedral interstitials and in Schottky defects along the 〈1 1 1〉 and 〈1 0 0〉 directions. We also analyze atomic displacements, volume modifications and Bader charges. This kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. This should deal as a starting point towards the study of the complex behavior of fission products in irradiated ThC.

  1. Quantal density functional theory II. Approximation methods and applications

    International Nuclear Information System (INIS)

    Sahni, Viraht

    2010-01-01

    This book is on approximation methods and applications of Quantal Density Functional Theory (QDFT), a new local effective-potential-energy theory of electronic structure. What distinguishes the theory from traditional density functional theory is that the electron correlations due to the Pauli exclusion principle, Coulomb repulsion, and the correlation contribution to the kinetic energy -- the Correlation-Kinetic effects -- are separately and explicitly defined. As such it is possible to study each property of interest as a function of the different electron correlations. Approximations methods based on the incorporation of different electron correlations, as well as a many-body perturbation theory within the context of QDFT, are developed. The applications are to the few-electron inhomogeneous electron gas systems in atoms and molecules, as well as to the many-electron inhomogeneity at metallic surfaces. (orig.)

  2. Magnetism, microstructure and First Principles calculations of atomized and annealed Ni{sub 3}Al

    Energy Technology Data Exchange (ETDEWEB)

    García-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Crespo, P.; Hernando, A. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Marín, P.; Velasco, V. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Ynduráin, F. [Dpto. de Física de la Materia Condensada, UAM, Cantoblanco, 28049 Madrid (Spain)

    2014-12-05

    Highlights: • The microstructure and order of as-atomized Ni{sub 3}Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni{sub 3}Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni{sub 3}Al, L1{sub 2}, phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position.

  3. Structural, electronic and optical properties of silver delafossite oxides: A first-principles study with hybrid functional

    International Nuclear Information System (INIS)

    Kumar, Mukesh; Persson, Clas

    2013-01-01

    Ternary delafossite compounds are potential materials for optoelectronic devices. Employing a first-principles method, we calculate the structural, electronic, and optical properties of the silver based compounds AgMO 2 (M=Al, Ga or In), which crystallize in delafossite structure. Our calculations show that these AgMO 2 oxides have indirect band gaps and the gap energies are in the region of 1.6–3.0 eV whereas, the lowest direct band gap energies are estimated in the range of 2.6–4.3 eV. Furthermore, we find that AgMO 2 compounds exhibit a strong anisotropy for the dielectric function and absorption spectra. The absorption onset for these compounds occurs well above the band gap energies. Overall, we show that the hybrid functional improves the lattice parameters and band gap energies and the calculated values are in good agreement with the experimental values

  4. First-principles study of Ga-vacancy induced magnetism in β-Ga2O3.

    Science.gov (United States)

    Yang, Ya; Zhang, Jihua; Hu, Shunbo; Wu, Yabei; Zhang, Jincang; Ren, Wei; Cao, Shixun

    2017-11-01

    First principles calculations based on density functional theory were performed to study the electronic structure and magnetic properties of β-Ga 2 O 3 in the presence of cation vacancies. We investigated two kinds of Ga vacancies at different symmetry sites and the consequent structural distortion and defect states. We found that both the six-fold coordinated octahedral site and the four-fold coordinated tetrahedral site vacancies can lead to a spin polarized ground state. Furthermore, the calculation identified a relationship between the spin polarization and the charge states of the vacancies, which might be explained by a molecular orbital model consisting of uncompensated O 2- 2p dangling bonds. The calculations for the two vacancy systems also indicated a potential long-range ferromagnetic order which is beneficial for spintronics application.

  5. First-principles study for the enhanced sulfur tolerance of Ni(1 1 1) surface alloyed with Pb

    Science.gov (United States)

    Zhang, Yanxing; Yang, Zongxian

    2018-04-01

    The adsorption of H2S, HS, S, H and the dissociation of H2S on the Ni2Pb/Ni (1 1 1) are systematically studied using the first-principles method based on density functional theory. It is found that H2S dissociation barriers are greatly increased by alloying with Pb atoms in the Ni(1 1 1) surface, while the barrier for H2S formation is greatly reduced. In addition, the adsorption of sulfur atom is weakened a lot. The results indicate that alloying with Pb may be a good way to increase the sulfur tolerance of Ni based anode catalysts of solid oxide fuel cells.

  6. First principles calculation of material properties of group IV elements and III-V compounds

    Science.gov (United States)

    Malone, Brad Dean

    first principles calculations of the quasiparticle and optical excitation spectra of recently predicted silicon and germanium polytypes in the body-centered-tetragonal (bct) structure. The quasiparticle spectra calculated within the GW approximation predict that both silicon and germanium in the bct structure are small band gap materials. The optical spectra are then evaluated by solving the Bethe-Salpeter equation taking into account. • We examine the low-pressure phases of Ge in Chapter 6 by performing first principles calculations of the electronic structure and lattice dynamics of the R8, BC8, ST12, and hexagonal diamond structures of Ge. To aid future experimental investigation, we include predictions of the Raman-active frequencies of these phases as well as present the full phonon dispersion throughout the zone. • In Chapter 7 we demonstrate how first principles calculations can be used to predict new structures. In a study aimed at finding new useful forms of silicon, we use an ab initio random structure searching (AIRSS) method to identify a new phase of silicon in the Ibamstructure. The Ibam phase is found to be semimetallic within density functional theory with a small band overlap, and it is expected that quasiparticle corrections using the GW approximation would yield a semiconducting state with a small band gap. • We present a first-principles study of boron and phosphorus substitutional defects in Si-XII in Chapter 8. Recent result from nanoindentation experiments reveal that the Si-XII phase is semiconducting and has the interesting property that it can be doped n- and p-type at room temperature without an annealing step. Using the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we examine the formation energies of the B and P defects at the two distinct atomic sites in Si-XII to find on which site the substitutional defects are more easily accommodated. We also estimate the thermodynamic transition levels of each defect in its relevant

  7. First principles design of a core bioenergetic transmembrane electron-transfer protein

    Energy Technology Data Exchange (ETDEWEB)

    Goparaju, Geetha; Fry, Bryan A.; Chobot, Sarah E.; Wiedman, Gregory; Moser, Christopher C.; Leslie Dutton, P.; Discher, Bohdana M.

    2016-05-01

    Here we describe the design, Escherichia coli expression and characterization of a simplified, adaptable and functionally transparent single chain 4-α-helix transmembrane protein frame that binds multiple heme and light activatable porphyrins. Such man-made cofactor-binding oxidoreductases, designed from first principles with minimal reference to natural protein sequences, are known as maquettes. This design is an adaptable frame aiming to uncover core engineering principles governing bioenergetic transmembrane electron-transfer function and recapitulate protein archetypes proposed to represent the origins of photosynthesis. This article is part of a Special Issue entitled Biodesign for Bioenergetics — the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

  8. First-principles and classical molecular dynamics study of threshold displacement energy in beryllium

    Energy Technology Data Exchange (ETDEWEB)

    Vladimirov, P.V. [Institute for Applied Materials – Applied Materials Physics, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe (Germany); Borodin, V.A., E-mail: Borodin_VA@nrcki.ru [National Research Center “Kurchatov Institute”, 123182 Moscow (Russian Federation); NRNU MEPhI, 115409 Moscow (Russian Federation)

    2017-02-15

    Highlights: • Beryllium is a functional material of future fusion reactors. • The threshold displacement energy by fast particles is studied. • Classical and first principles simulations are used. - Abstract: Beryllium selected as a neutron multiplier material for the tritium breeding blanket of fusion reactor should withstand high doses of fast neutron irradiation. The damage produced by irradiation is usually evaluated assuming that the number of atomic displacements to the threshold displacement energy, E{sub d}, which is considered as an intrinsic material parameter. In this work the value of E{sub d} for hcp beryllium is estimated simultaneously from classical and first-principles molecular dynamics simulations. Quite similar quantitative pictures of defect production are observed in both simulation types, though the predicted displacement threshold values seem to be approximately two times higher in the first-principles approach. We expect that, after more detailed first-principles investigations, this approach can be used for scaling the damage prediction predictions by classical molecular dynamics, opening a way for more consistent calculations of displacement damage in materials.

  9. First principles calculation of L21+A2 coherent equilibria in the Fe-Al-Ti system

    International Nuclear Information System (INIS)

    Alonso, Paula R.; Gargano, Pablo H.; Ramirez-Caballero, Gustavo E.; Balbuena, Perla B.; Rubiolo, Gerardo H.

    2009-01-01

    By combining first-principles density functional total energy calculations and statistical mechanics the ground state and the phase equilibria at finite temperatures of the ternary system Fe-Al-Ti have been investigated. Total energy calculations have been performed by means of the Wien 2k code to establish the ground state energetic. A cluster expansion method was therewith used to describe solid solutions. At several chosen finite temperatures the cluster variation method in the irregular tetrahedron approximation was employed in order to calculate the iron rich ternary bcc equilibria. It is confirmed that there are two kinds of phase separations of the bcc phase, A2+L2 1 and B2+L2 1 .

  10. A first principles study of the mechanical, electronic, and vibrational properties of lead oxide

    Science.gov (United States)

    Zhuravlev, Yu. N.; Korabel'nikov, D. V.

    2017-11-01

    The first principles study of the crystal structure, chemical bonds, elastic and mechanical properties, electron energy band structure and density, and normal long-wave vibrations of nine phases of lead monoxide, dioxide, and tetraoxide has been performed under normal and external pressure within the framework of density functional theory (DFT) with the Perdew-Becke-Ernzerhof (PBE) gradient exchange-correlation functional and its hybrid version with a 25-% Hartree-Fock (HF) exchange contribution in the basis of localized atom orbitals. The behavior of physical parameters has been studied using the cold four- and threeparameter equations of state. The parameters of the crystal structures are in satisfactory agreement with experimental data, and elastic constants indicate their mechanical stability and anisotropy in the elastic properties. The elasticity, shear, and Young moduli, hardness, acoustic velocities, and Debye temperature of dioxide on the one hand and monoxide and tetraoxide on the other hand appreciably differ from each other. The difference between electron properties may be explained by the character of hybridization in the upper filled and lower empty energy bands as evident from the density of states. In monoxide, the indirect band gap width decreases with increasing pressure at a rate of 0.16 eV/GPa, and the direct band gap width increases at a rate of 0.13 eV/GPa. To identify crystalline phases, the frequencies and intensities of long-wave modes active in IR and Raman spectra have been calculated.

  11. First-Principles Momentum Dependent Local Ansatz Approach to the Momentum Distribution Function in Iron-Group Transition Metals

    Science.gov (United States)

    Kakehashi, Yoshiro; Chandra, Sumal

    2017-03-01

    The momentum distribution function (MDF) bands of iron-group transition metals from Sc to Cu have been investigated on the basis of the first-principles momentum dependent local ansatz wavefunction method. It is found that the MDF for d electrons show a strong momentum dependence and a large deviation from the Fermi-Dirac distribution function along high-symmetry lines of the first Brillouin zone, while the sp electrons behave as independent electrons. In particular, the deviation in bcc Fe (fcc Ni) is shown to be enhanced by the narrow eg (t2g) bands with flat dispersion in the vicinity of the Fermi level. Mass enhancement factors (MEF) calculated from the jump on the Fermi surface are also shown to be momentum dependent. Large mass enhancements of Mn and Fe are found to be caused by spin fluctuations due to d electrons, while that for Ni is mainly caused by charge fluctuations. Calculated MEF are consistent with electronic specific heat data as well as recent angle resolved photoemission spectroscopy data.

  12. First-Principle Study of the Optical Properties of Dilute-P GaN1-xPx Alloys.

    Science.gov (United States)

    Borovac, Damir; Tan, Chee-Keong; Tansu, Nelson

    2018-04-16

    An investigation on the optical properties of dilute-P GaN 1-x P x alloys by First-Principle Density Functional Theory (DFT) methods is presented, for phosphorus (P) content varying from 0% up to 12.5%. Findings on the imaginary and real part of the dielectric function are analyzed and the results are compared with previously reported theoretical works on GaN. The complex refractive index, normal-incidence reflectivity and birefringence are presented and a difference in the refractive index in the visible regime between GaN and GaNP alloys of ~0.3 can be engineered by adding minute amounts of phosphorus, indicating strong potential for refractive index tunability. The optical properties of the GaN 1-x P x alloys indicate their strong potential for implementation in various III-nitride-based photonic waveguide applications and Distributed Bragg Reflectors (DBR).

  13. Quasiparticles and phonon satellites in spectral functions of semiconductors and insulators: Cumulants applied to the full first-principles theory and the Fröhlich polaron

    Science.gov (United States)

    Nery, Jean Paul; Allen, Philip B.; Antonius, Gabriel; Reining, Lucia; Miglio, Anna; Gonze, Xavier

    2018-03-01

    The electron-phonon interaction causes thermal and zero-point motion shifts of electron quasiparticle (QP) energies ɛk(T ) . Other consequences of interactions, visible in angle-resolved photoemission spectroscopy (ARPES) experiments, are broadening of QP peaks and appearance of sidebands, contained in the electron spectral function A (k ,ω ) =-ℑ m GR(k ,ω ) /π , where GR is the retarded Green's function. Electronic structure codes (e.g., using density-functional theory) are now available that compute the shifts and start to address broadening and sidebands. Here we consider MgO and LiF, and determine their nonadiabatic Migdal self-energy. The spectral function obtained from the Dyson equation makes errors in the weight and energy of the QP peak and the position and weight of the phonon-induced sidebands. Only one phonon satellite appears, with an unphysically large energy difference (larger than the highest phonon energy) with respect to the QP peak. By contrast, the spectral function from a cumulant treatment of the same self-energy is physically better, giving a quite accurate QP energy and several satellites approximately spaced by the LO phonon energy. In particular, the positions of the QP peak and first satellite agree closely with those found for the Fröhlich Hamiltonian by Mishchenko et al. [Phys. Rev. B 62, 6317 (2000), 10.1103/PhysRevB.62.6317] using diagrammatic Monte Carlo. We provide a detailed comparison between the first-principles MgO and LiF results and those of the Fröhlich Hamiltonian. Such an analysis applies widely to materials with infrared(IR)-active phonons.

  14. Self-consistent embedding of density-matrix renormalization group wavefunctions in a density functional environment.

    Science.gov (United States)

    Dresselhaus, Thomas; Neugebauer, Johannes; Knecht, Stefan; Keller, Sebastian; Ma, Yingjin; Reiher, Markus

    2015-01-28

    We present the first implementation of a density matrix renormalization group algorithm embedded in an environment described by density functional theory. The frozen density embedding scheme is used with a freeze-and-thaw strategy for a self-consistent polarization of the orbital-optimized wavefunction and the environmental densities with respect to each other.

  15. Clean Os(0001) electronic surface states: A first-principle fully relativistic investigation

    Science.gov (United States)

    Urru, Andrea; Dal Corso, Andrea

    2018-05-01

    We analyze the electronic structure of the Os(0001) surface by means of first-principle calculations based on Fully Relativistic (FR) Density Functional Theory (DFT) and a Projector Augmented-Wave (PAW) approach. We investigate surface states and resonances analyzing their spin-orbit induced energy splitting and their spin polarization. The results are compared with previously studied surfaces Ir(111), Pt(111), and Au(111). We do not find any surface state in the gap similar to the L-gap of the (111) fcc surfaces, but find Rashba split resonances that cross the Fermi level and, as in the recently studied Ir(111) surface, have a characteristic downward dispersion. Moreover, for some selected surface states we study the spin polarization with respect to k∥, the wave-vector parallel to the surface. In some cases, such as the Rashba split resonances, the spin polarization shows a smooth behavior with slow rotations, in others the rotation is faster, due to mixing and anti-crossing of the states.

  16. Density matrix in quantum electrodynamics, equivalence principle and Hawking effect

    International Nuclear Information System (INIS)

    Frolov, V.P.; Gitman, D.M.

    1978-01-01

    The expression for the density matrix describing particles of one sort (electrons or positrons) created by an external electromagnetic field from the vacuum is obtained. The explicit form of the density matrix is found for the case of constant and uniform electric field. Arguments are given for the presence of a connection between the thermal nature of the density matrix describing particles created by the gravitational field of a black hole and the equivalence principle. (author)

  17. Density-functional expansion methods: Grand challenges.

    Science.gov (United States)

    Giese, Timothy J; York, Darrin M

    2012-03-01

    We discuss the source of errors in semiempirical density functional expansion (VE) methods. In particular, we show that VE methods are capable of well-reproducing their standard Kohn-Sham density functional method counterparts, but suffer from large errors upon using one or more of these approximations: the limited size of the atomic orbital basis, the Slater monopole auxiliary basis description of the response density, and the one- and two-body treatment of the core-Hamiltonian matrix elements. In the process of discussing these approximations and highlighting their symptoms, we introduce a new model that supplements the second-order density-functional tight-binding model with a self-consistent charge-dependent chemical potential equalization correction; we review our recently reported method for generalizing the auxiliary basis description of the atomic orbital response density; and we decompose the first-order potential into a summation of additive atomic components and many-body corrections, and from this examination, we provide new insights and preliminary results that motivate and inspire new approximate treatments of the core-Hamiltonian.

  18. The elastic and thermodynamic properties of ZrMo2 from first principles calculations

    International Nuclear Information System (INIS)

    Liu, Xian-Kun; Zhou, Wei; Zheng, Zhou; Peng, Shu-Ming

    2014-01-01

    Highlights: • Elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are calculated by first principles. • Mechanical stability is testified from elastic constants at zero pressure. • Phonon scattering of ZrMo 2 under different temperature are obtained. - Abstract: The elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are investigated by first-principles calculations based on pseudopotential plane-wave density functional theory (DFT) within the generalized gradient approximation (GGA) and quasi-harmonic Debye model. The calculated lattice parameters are in good agreement with the available experimental data. The calculated elastic constants of ZrMo 2 increase monotonically with increasing pressure, and the relationship between the elastic constants and pressure show that ZrMo 2 satisfies the mechanical stability criteria under applied pressure (0–65 GPa). The related mechanical properties such as bulk modulus (B), shear modulus (G), Young’s modulus (E), and Poisson’s ratio (v) are also studied for polycrystalline of ZrMo 2 . The calculated B/G value shows that ZrMo 2 behaves in a ductile manner, and higher pressure can significantly improve the ductility of ZrMo 2 . The pressure and temperature dependencies of the relative volume, the bulk modulus, the elastic constants, the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameters are obtained and discussed by the quasi-harmonic Debye model in the ranges of 0–1800 K and 0–65 GPa

  19. First-principles study of dielectric properties of cerium oxide

    International Nuclear Information System (INIS)

    Yamamoto, Takenori; Momida, Hiroyoshi; Hamada, Tomoyuki; Uda, Tsuyoshi; Ohno, Takahisa

    2005-01-01

    We have theoretically investigated the dielectric properties of fluorite CeO 2 as well as hexagonal and cubic Ce 2 O 3 by using first-principles pseudopotentials techniques within the local density approximation. Calculated electronic and lattice dielectric constants of CeO 2 are in good agreement with previous theoretical and experimental results. For Ce 2 O 3 , the hexagonal phase has a lattice dielectric constant comparable to that of CeO 2 , whereas the cubic phase has a much smaller one. We have concluded that the enhancement of the dielectric constant in CeO 2 epitaxially grown on Si is not due to its lattice expansion experimentally observed nor regular formation of oxygen vacancies in CeO 2

  20. Density dependence of the nuclear energy-density functional

    Science.gov (United States)

    Papakonstantinou, Panagiota; Park, Tae-Sun; Lim, Yeunhwan; Hyun, Chang Ho

    2018-01-01

    Background: The explicit density dependence in the coupling coefficients entering the nonrelativistic nuclear energy-density functional (EDF) is understood to encode effects of three-nucleon forces and dynamical correlations. The necessity for the density-dependent coupling coefficients to assume the form of a preferably small fractional power of the density ρ is empirical and the power is often chosen arbitrarily. Consequently, precision-oriented parametrizations risk overfitting in the regime of saturation and extrapolations in dilute or dense matter may lose predictive power. Purpose: Beginning with the observation that the Fermi momentum kF, i.e., the cubic root of the density, is a key variable in the description of Fermi systems, we first wish to examine if a power hierarchy in a kF expansion can be inferred from the properties of homogeneous matter in a domain of densities, which is relevant for nuclear structure and neutron stars. For subsequent applications we want to determine a functional that is of good quality but not overtrained. Method: For the EDF, we fit systematically polynomial and other functions of ρ1 /3 to existing microscopic, variational calculations of the energy of symmetric and pure neutron matter (pseudodata) and analyze the behavior of the fits. We select a form and a set of parameters, which we found robust, and examine the parameters' naturalness and the quality of resulting extrapolations. Results: A statistical analysis confirms that low-order terms such as ρ1 /3 and ρ2 /3 are the most relevant ones in the nuclear EDF beyond lowest order. It also hints at a different power hierarchy for symmetric vs. pure neutron matter, supporting the need for more than one density-dependent term in nonrelativistic EDFs. The functional we propose easily accommodates known or adopted properties of nuclear matter near saturation. More importantly, upon extrapolation to dilute or asymmetric matter, it reproduces a range of existing microscopic

  1. First-Principles and Thermodynamic Simulation of Elastic Stress Effect on Energy of Hydrogen Dissolution in Alpha Iron

    Science.gov (United States)

    Rakitin, M. S.; Mirzoev, A. A.; Mirzaev, D. A.

    2018-04-01

    Mobile hydrogen, when dissolving in metals, redistributes due to the density gradients and elastic stresses, and enables destruction processes or phase transformations in local volumes of a solvent metal. It is rather important in solid state physics to investigate these interactions. The first-principle calculations performed in terms of the density functional theory, are used for thermodynamic simulation of the elastic stress effect on the energy of hydrogen dissolution in α-Fe crystal lattice. The paper presents investigations of the total energy of Fe-H system depending on the lattice parameter. As a result, the relation is obtained between the hydrogen dissolution energy and stress. A good agreement is shown between the existing data and simulation results. The extended equation is suggested for the chemical potential of hydrogen atom in iron within the local stress field. Two parameters affecting the hydrogen distribution are compared, namely local stress and phase transformations.

  2. Intrinsic-density functionals

    International Nuclear Information System (INIS)

    Engel, J.

    2007-01-01

    The Hohenberg-Kohn theorem and Kohn-Sham procedure are extended to functionals of the localized intrinsic density of a self-bound system such as a nucleus. After defining the intrinsic-density functional, we modify the usual Kohn-Sham procedure slightly to evaluate the mean-field approximation to the functional, and carefully describe the construction of the leading corrections for a system of fermions in one dimension with a spin-degeneracy equal to the number of particles N. Despite the fact that the corrections are complicated and nonlocal, we are able to construct a local Skyrme-like intrinsic-density functional that, while different from the exact functional, shares with it a minimum value equal to the exact ground-state energy at the exact ground-state intrinsic density, to next-to-leading order in 1/N. We briefly discuss implications for real Skyrme functionals

  3. First principles study of structural, electronic and optical properties of polymorphic forms of Rb 2Te

    Science.gov (United States)

    Alay-e-Abbas, S. M.; Shaukat, A.

    2011-05-01

    First-principles density functional theory calculations have been performed for structural, electronic and optical properties of three polymorphic forms of rubidium telluride. Our calculations show that the sequence of pressure induced phase transitions for Rb 2Te is Fm3¯m → Pnma → P6 3/mmc which is governed by the coordination numbers of the anions. From our calculated low transition pressure value for the Fm3¯m phase to the Pnma phase transition of Rb 2Te, the experimentally observed meta-stability of Fm3¯m phase at ambient conditions seems reasonable. The electronic band structure has been calculated for all the three phases and the change in the energy band gap is discussed for the transitioning phases. The energy band gaps obtained for the three phases of Rb 2Te decrease on going from the meta-stable phase to the high-pressure phases. Total and partial density of states for the polymorphs of Rb 2Te has been computed to elucidate the contribution of various atomic states on the electronic band structure. Furthermore, optical properties for all the polymorphic forms have been presented in form of the complex dielectric function.

  4. Electric field effect of GaAs monolayer from first principles

    Directory of Open Access Journals (Sweden)

    Jiongyao Wu

    2017-03-01

    Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

  5. Theoretical investigation of pressure-induced structural transitions in americium using GGA+U and hybrid density functional theory methods

    DEFF Research Database (Denmark)

    Verma, Ashok K.; Modak, P.; Sharma, Surinder M.

    2013-01-01

    First-principles calculations have been performed for americium (Am) metal using the generalized gradient approximation + orbital-dependent onsite Coulomb repulsion via Hubbard interaction (GGA+U) and hybrid density functional theory (HYB-DFT) methods to investigate various ground state properties......-I to Am-II transition. Good agreement was found between calculated and experimental equations of states for all phases, but the first three phases need larger U (α) parameters (where α represents the fraction of Hartree-Fock exchange energy replacing the DFT exchange energy) than the fourth phase in order...

  6. Quantum maximum-entropy principle for closed quantum hydrodynamic transport within a Wigner function formalism

    International Nuclear Information System (INIS)

    Trovato, M.; Reggiani, L.

    2011-01-01

    By introducing a quantum entropy functional of the reduced density matrix, the principle of quantum maximum entropy is asserted as fundamental principle of quantum statistical mechanics. Accordingly, we develop a comprehensive theoretical formalism to construct rigorously a closed quantum hydrodynamic transport within a Wigner function approach. The theoretical formalism is formulated in both thermodynamic equilibrium and nonequilibrium conditions, and the quantum contributions are obtained by only assuming that the Lagrange multipliers can be expanded in powers of (ℎ/2π) 2 . In particular, by using an arbitrary number of moments, we prove that (1) on a macroscopic scale all nonlocal effects, compatible with the uncertainty principle, are imputable to high-order spatial derivatives, both of the numerical density n and of the effective temperature T; (2) the results available from the literature in the framework of both a quantum Boltzmann gas and a degenerate quantum Fermi gas are recovered as a particular case; (3) the statistics for the quantum Fermi and Bose gases at different levels of degeneracy are explicitly incorporated; (4) a set of relevant applications admitting exact analytical equations are explicitly given and discussed; (5) the quantum maximum entropy principle keeps full validity in the classical limit, when (ℎ/2π)→0.

  7. Density functional theory study of Al-doped hematite

    International Nuclear Information System (INIS)

    Rivera, Richard; Stashans, Arvids; Piedra, Lorena; Pinto, Henry P

    2012-01-01

    Using first-principles density functional theory calculations within the generalized gradient approximation (GGA) as well as the GGA+U approach, we study Al-doped α-Fe 2 O 3 crystals. Structural, electronic, magnetic and optical properties due to impurity incorporation have been investigated and discussed in detail. Atomic displacements and Bader charges on atoms have been computed, showing that Al dopant converts the chemical bonding in its neighbourhood into a more ionic one. This work enhances our knowledge about how a crystalline lattice reacts in the presence of an Al impurity. It was found that Al incorporation produces some local changes in the band structure of the material without the creation of local energy levels within the band gap. The results provide evidence for changes in the magnetic moments in the vicinity of a defect, which means that α-Fe 2 O 3 doped with aluminum might not act as an antiferromagnetic substance.

  8. Prediction of thermodynamic properties of solute elements in Si solutions using first-principles calculations

    International Nuclear Information System (INIS)

    Iwata, K.; Matsumiya, T.; Sawada, H.; Kawakami, K.

    2003-01-01

    The method is presented to predict the activity coefficients and the interaction parameters of the solute elements in infinite dilute Si solutions by the use of first-principles calculations based on density functional theory. In this method, the regular solution model is assumed. The calculated activity coefficients in solid Si are converted to those in molten Si by the use of the solid-liquid partition coefficients. Furthermore, the interaction parameters in solid Si solutions are calculated and compared with reported experimental values of those in liquid Si solutions. The results show that the calculated activity coefficients and interaction parameters of Al, Fe, Ti and Pb in Si solutions are in good agreement with the tendency of the experiments. However, the calculations have some quantitative discrepancy from the experiments. It is expected that consideration of the excess entropy would reduce this discrepancy

  9. Optoelectronic and magnetic properties of Mn-doped indium tin oxide: A first-principles study

    Science.gov (United States)

    Nath Tripathi, Madhvendra; Saeed Bahramy, Mohammad; Shida, Kazuhito; Sahara, Ryoji; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

    2012-10-01

    The manganese doped indium tin oxide (ITO) has integrated magnetics, electronics, and optical properties for next generation multifunctional devices. Our first-principles density functional theory (DFT) calculations show that the manganese atom replaces b-site indium atom, located at the second coordination shell of the interstitial oxygen in ITO. It is also found that both anti-ferromagnetic and ferromagnetic behaviors are realizable. The calculated magnetic moment of 3.95μB/Mn as well as the high transmittance of ˜80% for a 150 nm thin film of Mn doped ITO is in good agreement with the experimental data. The inclusion of on-site Coulomb repulsion corrections via DFT + U methods turns out to improve the optical behavior of the system. The optical behaviors of this system reveal its suitability for the magneto-opto-electronic applications.

  10. Rock-salt structure lithium deuteride formation in liquid lithium with high-concentrations of deuterium: a first-principles molecular dynamics study

    Science.gov (United States)

    Chen, Mohan; Abrams, T.; Jaworski, M. A.; Carter, Emily A.

    2016-01-01

    Because of lithium’s possible use as a first wall material in a fusion reactor, a fundamental understanding of the interactions between liquid lithium (Li) and deuterium (D) is important. We predict structural and dynamical properties of liquid Li samples with high concentrations of D, as derived from first-principles molecular dynamics simulations. Liquid Li samples with four concentrations of inserted D atoms (LiDβ , β =0.25 , 0.50, 0.75, and 1.00) are studied at temperatures ranging from 470 to 1143 K. Densities, diffusivities, pair distribution functions, bond angle distribution functions, geometries, and charge transfer between Li and D atoms are calculated and analyzed. The analysis suggests liquid-solid phase transitions can occur at some concentrations and temperatures, forming rock-salt LiD within liquid Li. We also observe formation of some D2 molecules at high D concentrations.

  11. Energy vs. density on paths toward more exact density functionals.

    Science.gov (United States)

    Kepp, Kasper P

    2018-03-14

    Recently, the progression toward more exact density functional theory has been questioned, implying a need for more formal ways to systematically measure progress, i.e. a "path". Here I use the Hohenberg-Kohn theorems and the definition of normality by Burke et al. to define a path toward exactness and "straying" from the "path" by separating errors in ρ and E[ρ]. A consistent path toward exactness involves minimizing both errors. Second, a suitably diverse test set of trial densities ρ' can be used to estimate the significance of errors in ρ without knowing the exact densities which are often inaccessible. To illustrate this, the systems previously studied by Medvedev et al., the first ionization energies of atoms with Z = 1 to 10, the ionization energy of water, and the bond dissociation energies of five diatomic molecules were investigated using CCSD(T)/aug-cc-pV5Z as benchmark at chemical accuracy. Four functionals of distinct designs was used: B3LYP, PBE, M06, and S-VWN. For atomic cations regardless of charge and compactness up to Z = 10, the energy effects of the different ρ are energy-wise insignificant. An interesting oscillating behavior in the density sensitivity is observed vs. Z, explained by orbital occupation effects. Finally, it is shown that even large "normal" problems such as the Co-C bond energy of cobalamins can use simpler (e.g. PBE) trial densities to drastically speed up computation by loss of a few kJ mol -1 in accuracy. The proposed method of using a test set of trial densities to estimate the sensitivity and significance of density errors of functionals may be useful for testing and designing new balanced functionals with more systematic improvement of densities and energies.

  12. Role of A-site Ca and B-site Zr substitution in BaTiO3 lead-free compounds: Combined experimental and first principles density functional theoretical studies

    Science.gov (United States)

    Keswani, Bhavna C.; Saraf, Deepashri; Patil, S. I.; Kshirsagar, Anjali; James, A. R.; Kolekar, Y. D.; Ramana, C. V.

    2018-05-01

    We report on the combined experimental and theoretical simulation results of lead-free ferroelectrics, Ba(1-x)CaxTiO3 (x = 0.0-0.3) and BaTi(1-y)ZryO3 (y = 0.0-0.2), synthesized by standard solid state reaction method. First principles density functional calculations are used to investigate the electronic structure, dynamical charges, and spontaneous polarization of these compounds. In addition, the structural, ferroelectric, piezoelectric, and dielectric properties are studied using extensive experiments. The X-ray diffraction and temperature dependent Raman spectroscopy studies indicate that the calcium (Ca) substituted compositions exhibit a single phase crystal structure, while zirconium (Zr) substituted compositions are biphasic. The scanning electron micrographs reveal the uniform and highly dense microstructure. The presence of polarization-electric field and strain-electric field hysteresis loops confirms the ferroelectric and piezoelectric nature of all the compositions. Our results demonstrate higher values for polarization, percentage strain, piezoelectric coefficients, and electrostrictive coefficient compared to those existing in the literature. For smaller substitutions of Ca and Zr in BaTiO3, a direct piezoelectric coefficient (d33) is enhanced, while the highest d33 value (˜300 pC/N) is observed for BaTi0.96Zr0.04O3 due to the biphasic ferroelectric behavior. Calculation of Born effective charges indicates that doping with Ca or Zr increases the dynamical charges on Ti as well as on O and decreases the dynamical charge on Ba. An increase in the dynamical charges on Ti and O is ascribed to the increase in covalency of Ti-O bond that reduces the polarizability of the crystal. A broader range of temperatures is demonstrated to realize the stable phase in the Ca substituted compounds. The results indicate enhancement in the temperature range of applicability of these compounds for device applications. The combined theoretical and experimental study is

  13. Versatile Density Functionals for Computational Surface Science

    DEFF Research Database (Denmark)

    Wellendorff, Jess

    Density functional theory (DFT) emerged almost 50 years ago. Since then DFT has established itself as the central electronic structure methodology for simulating atomicscale systems from a few atoms to a few hundred atoms. This success of DFT is due to a very favorable accuracy-to-computational c......Density functional theory (DFT) emerged almost 50 years ago. Since then DFT has established itself as the central electronic structure methodology for simulating atomicscale systems from a few atoms to a few hundred atoms. This success of DFT is due to a very favorable accuracy...... resampling techniques, thereby systematically avoiding problems with overfitting. The first ever density functional presenting both reliable accuracy and convincing error estimation is generated. The methodology is general enough to be applied to more complex functional forms with higher-dimensional fitting...

  14. Time-Dependent Density Functional Theory for Open Systems and Its Applications.

    Science.gov (United States)

    Chen, Shuguang; Kwok, YanHo; Chen, GuanHua

    2018-02-20

    Photovoltaic devices, electrochemical cells, catalysis processes, light emitting diodes, scanning tunneling microscopes, molecular electronics, and related devices have one thing in common: open quantum systems where energy and matter are not conserved. Traditionally quantum chemistry is confined to isolated and closed systems, while quantum dissipation theory studies open quantum systems. The key quantity in quantum dissipation theory is the reduced system density matrix. As the reduced system density matrix is an O(M! × M!) matrix, where M is the number of the particles of the system of interest, quantum dissipation theory can only be employed to simulate systems of a few particles or degrees of freedom. It is thus important to combine quantum chemistry and quantum dissipation theory so that realistic open quantum systems can be simulated from first-principles. We have developed a first-principles method to simulate the dynamics of open electronic systems, the time-dependent density functional theory for open systems (TDDFT-OS). Instead of the reduced system density matrix, the key quantity is the reduced single-electron density matrix, which is an N × N matrix where N is the number of the atomic bases of the system of interest. As the dimension of the key quantity is drastically reduced, the TDDFT-OS can thus be used to simulate the dynamics of realistic open electronic systems and efficient numerical algorithms have been developed. As an application, we apply the method to study how quantum interference develops in a molecular transistor in time domain. We include electron-phonon interaction in our simulation and show that quantum interference in the given system is robust against nuclear vibration not only in the steady state but also in the transient dynamics. As another application, by combining TDDFT-OS with Ehrenfest dynamics, we study current-induced dissociation of water molecules under scanning tunneling microscopy and follow its time dependent

  15. The structural, elastic, electronic and dynamical properties of chalcopyrite semiconductor BeGeAs{sub 2} from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Ciftci, Yasemin Oe. [Gazi University Teknikokullar, Department of Physics, Faculty of Sciences, Ankara (Turkey); Evecen, Meryem; Aldirmaz, Emine [Amasya University, Department of Physics, Faculty of Arts and Sciences, Amasya (Turkey)

    2017-01-15

    First-principles calculations for the structural, elastic, electronic and vibrational properties of BeGeAs{sub 2} with chalcopyrite structure have been reported in the frame work of the density functional theory. The calculated ground state properties are in good agreement with the available data. By considering the electronic band structure and electronic density of states calculation, it is found that this compound is a semiconductor which confirmed the previous work. Single-crystal elastic constants and related properties such as Young's modulus, Poisson ratio, shear modulus and bulk modulus have been predicted using the stress-finite strain technique. It can be seen from the calculated elastic constants that this compound is mechanically stable in the chalcopyrite structure. Pressure dependences of elastic constants and band gap are also reported. Finally, the phonon dispersion curves and total and partial density of states were calculated and discussed. The calculated phonon frequencies BeGeAs{sub 2} are positive, indicating the dynamical stability of the studied compound. (orig.)

  16. First principles calculations of optical properties of the armchair SiC nanoribbons with O, F and H termination

    Science.gov (United States)

    Lu, Dao-Bang; Song, Yu-Ling

    2018-03-01

    Based on density functional theory, we perform first-principles investigations to study the optical properties of the O-, F- and H-terminated SiC nanoribbons with armchair edges (ASiCNRs). By irradiating with an external electromagnetic field, we calculate the dielectric function, reflection spectra, energy loss coefficient and the real part of the conductance. It is demonstrated that the optical constants are sensitive to the low-energy range, different terminal atoms do not make much difference in the shape of the curves of the optical constants for the same-width ASiCNR, and the optical constants of wider nanoribbons usually have higher peaks than that of the narrower ones in low energy range. We hope that our study helps in experimental technology of fabricating high-quality SiC-based nanoscale photoelectric device.

  17. Progress towards an effective model for FeSe from high-accuracy first-principles quantum Monte Carlo

    Science.gov (United States)

    Busemeyer, Brian; Wagner, Lucas K.

    While the origin of superconductivity in the iron-based materials is still controversial, the proximity of the superconductivity to magnetic order is suggestive that magnetism may be important. Our previous work has suggested that first-principles Diffusion Monte Carlo (FN-DMC) can capture magnetic properties of iron-based superconductors that density functional theory (DFT) misses, but which are consistent with experiment. We report on the progress of efforts to find simple effective models consistent with the FN-DMC description of the low-lying Hilbert space of the iron-based superconductor, FeSe. We utilize a procedure outlined by Changlani et al.[1], which both produces parameter values and indications of whether the model is a good description of the first-principles Hamiltonian. Using this procedure, we evaluate several models of the magnetic part of the Hilbert space found in the literature, as well as the Hubbard model, and a spin-fermion model. We discuss which interaction parameters are important for this material, and how the material-specific properties give rise to these interactions. U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Scientific Discovery through Advanced Computing (SciDAC) program under Award No. FG02-12ER46875, as well as the NSF Graduate Research Fellowship Program.

  18. The first-principles calculations for the elastic properties of Zr2Al under compression

    International Nuclear Information System (INIS)

    Yuan Xiaoli; Wei Dongqing; Chen Xiangrong; Zhang Qingming; Gong Zizheng

    2011-01-01

    Graphical abstract: The calculated elastic constants C ij as a function of pressure P. Display Omitted Research highlights: → It is found that the five independent elastic constants increase monotonically with pressure. C 11 and C 33 vary rapidly as pressure increases, C 13 and C 12 becomes moderate. However, C 44 increases comparatively slowly with pressure. Figure shows excellent satisfaction of the calculated elastic constants of Zr 2 Al to these equations and hence in our calculation, the Zr 2 Al is mechanically stable at pressure up to 100 GPa. - Abstract: The first-principles calculations were applied to investigate the structural, elastic constants of Zr 2 Al alloy with increasing pressure. These properties are based on the plane wave pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for exchange and correlation. The result of the heat of formation of Zr 2 Al crystal investigated is in excellent consistent with results from other study. The anisotropy, the shear modulus, and Young's modulus for the ideal polycrystalline Zr 2 Al are also studied. It is found that (higher) pressure can significantly improve the ductility of Zr 2 Al. Moreover, the elastic constants of Zr 2 Al increase monotonically and the anisotropies decrease with the increasing pressure. Finally, it is observed that Zr d electrons are mainly contributed to the density of states at the Fermi level.

  19. Probability density functions for CP-violating rephasing invariants

    Science.gov (United States)

    Fortin, Jean-François; Giasson, Nicolas; Marleau, Luc

    2018-05-01

    The implications of the anarchy principle on CP violation in the lepton sector are investigated. A systematic method is introduced to compute the probability density functions for the CP-violating rephasing invariants of the PMNS matrix from the Haar measure relevant to the anarchy principle. Contrary to the CKM matrix which is hierarchical, it is shown that the Haar measure, and hence the anarchy principle, are very likely to lead to the observed PMNS matrix. Predictions on the CP-violating Dirac rephasing invariant |jD | and Majorana rephasing invariant |j1 | are also obtained. They correspond to 〈 |jD | 〉 Haar = π / 105 ≈ 0.030 and 〈 |j1 | 〉 Haar = 1 / (6 π) ≈ 0.053 respectively, in agreement with the experimental hint from T2K of | jDexp | ≈ 0.032 ± 0.005 (or ≈ 0.033 ± 0.003) for the normal (or inverted) hierarchy.

  20. First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys

    KAUST Repository

    Noor, Naveed Ahmed

    2010-10-01

    Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS are estimated in the range 0 ≤ x ≤ 1 using both the standard local density approximation (LDA) as well as the generalized gradient approximations (GGA) of Wu-Cohen (WC) for the exchange-correlation potential. It is observed that the direct band gap EgΓ-Γ of CdxZn1-xS decreases nonlinearly with the compositional parameter x, as observed experimentally. It is also found that Cd s and d, S p and Zn d states play a major role in determining the electronic properties of this alloy system. Furthermore, results for complex dielectric constant ε(ω), refractive index n(ω), normal-incidence reflectivity R(ω), absorption coefficient α(ω) and optical conductivity σ(ω) are also described in a wide range of the incident photon energy and compared with the existing experimental data. © 2010 Elsevier B.V. All rights reserved.

  1. Toward a Monte Carlo program for simulating vapor-liquid phase equilibria from first principles

    Energy Technology Data Exchange (ETDEWEB)

    McGrath, M; Siepmann, J I; Kuo, I W; Mundy, C J; Vandevondele, J; Sprik, M; Hutter, J; Mohamed, F; Krack, M; Parrinello, M

    2004-10-20

    Efficient Monte Carlo algorithms are combined with the Quickstep energy routines of CP2K to develop a program that allows for Monte Carlo simulations in the canonical, isobaric-isothermal, and Gibbs ensembles using a first principles description of the physical system. Configurational-bias Monte Carlo techniques and pre-biasing using an inexpensive approximate potential are employed to increase the sampling efficiency and to reduce the frequency of expensive ab initio energy evaluations. The new Monte Carlo program has been validated through extensive comparison with molecular dynamics simulations using the programs CPMD and CP2K. Preliminary results for the vapor-liquid coexistence properties (T = 473 K) of water using the Becke-Lee-Yang-Parr exchange and correlation energy functionals, a triple-zeta valence basis set augmented with two sets of d-type or p-type polarization functions, and Goedecker-Teter-Hutter pseudopotentials are presented. The preliminary results indicate that this description of water leads to an underestimation of the saturated liquid density and heat of vaporization and, correspondingly, an overestimation of the saturated vapor pressure.

  2. The helium effect at grain boundaries in Fe-Cr alloys: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Zemła, M.R., E-mail: marcin.zemla@wimpw.edu.pl [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland); Wróbel, J.S.; Wejrzanowski, T. [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland); Nguyen-Manh, D. [CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Kurzydłowski, K.J. [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland)

    2017-02-15

    Helium is produced in the structural materials in nuclear power plants by nuclear transmutation following neutron irradiation. Since the solubility of helium in all metals is extremely low, helium tends to be trapped at defects such as vacancies, dislocations and grain boundaries, which cause material embrittlement. Density functional theory (DFT) calculations were performed in order to investigate the helium effect at grain boundaries (GBs) in iron-chromium alloys. Both cohesive energy and magnetic properties at symmetric Σ3(1 1 1) and Σ5(2 1 0) tilt Fe GBs are studied in the presence of Cr and He atoms. It is found that the presence of Cr atoms increases cohesive energy, at different He concentrations, and strongly influences magnetic properties at the GBs. The effect of the segregation energy of helium atom as a function of the different positions of Cr atoms located inside/outside a GB has been considered. Results of the present first-principles study enable one to clarify the role of Cr in understanding the helium effect in Fe-Cr-based alloys.

  3. First principles simulations of antiphase defects on the SP 900 partial dislocation in silicon

    International Nuclear Information System (INIS)

    Valladares, Alexander; Sutton, A P

    2006-01-01

    We study the structure and energies of formation of antiphase defects on the single period (SP) 90 0 partial dislocation in silicon using a first principles density functional method. We consider two types of antiphase defect, the type first proposed by Hirsch (1980 J. Microsc. 118 3) wholly inside the dislocation core, and another type that lies partly outside the core. Both types are stable and contain one atom which is threefold coordinated. Each of these atoms has a dangling hybrid which lies in a direction perpendicular to the dislocation line on the slip plane. We obtain values of 1.39 ± 0.03 eV and 1.41 ± 0.03 eV for the average formation energy of single antiphase defects of the inside and outside types, respectively. We have obtained, using a tight binding scheme, band structures corresponding to these two types of defect, and we find both of them to be associated with states in the gap and each dangling hybrid to contain one electron

  4. Novel Natural Convection Heat Sink Design Concepts From First Principles

    Science.gov (United States)

    2016-06-01

    CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES by Derek E. Fletcher June 2016 Thesis Advisor: Garth Hobson Second Reader...COVERED Master’s Thesis 4. TITLE AND SUBTITLE NOVEL NATURAL CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES 5. FUNDING NUMBERS 6...CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES Derek E. Fletcher Lieutenant Commander, United States Navy B.S., Southwestern

  5. Energy band modulation of graphane by hydrogen-vacancy chains: A first-principles study

    Directory of Open Access Journals (Sweden)

    Bi-Ru Wu

    2014-08-01

    Full Text Available We investigated a variety of configurations of hydrogen-vacancy chains in graphane by first-principles density functional calculation. We found that graphane with two zigzag H-vacancy chains segregated by one or more H chain is generally a nonmagnetic conductor or has a negligible band gap. However, the same structure is turned into a semiconductor and generates a magnetic moment if either one or both of the vacancy chains are blocked by isolated H atoms. If H-vacancy chains are continuously distributed, the structure is similar to a zigzag graphene nanoribbon embedded in graphane. It was also found that the embedded zigzag graphene nanoribbon is antiferromagnetic, and isolated H atoms left in the 2-chain nanoribbon can tune the band gap and generate net magnetic moments. Similar effects are also obtained if bare carbon atoms are present outside the nanoribbon. These results are useful for designing graphene-based nanoelectronic circuits.

  6. Contrastive thermoelectric properties of strained SnSe crystals from the first-principles calculations

    Science.gov (United States)

    Tang, Yu; Cheng, Feng; Li, Decong; Deng, Shuping; Chen, Zhong; Sun, Luqi; Liu, Wenting; Shen, Lanxian; Deng, Shukang

    2018-06-01

    SnSe is a promising thermoelectric material with a record high dimensionless figure of merit ZT at high temperature ∼923 K. However, the ZT values for low-Temperature Pnma phase SnSe are just 0.1-0.9. Here, we use First-principle combine with Boltzmann transport theory methods to study the effect of tensile and compressible strain on the thermoelectric transport properties. The power factor of SnSe with -4% strain have a large boost along b and c directions of 7.7 and 3.9 μW cm-1 K-2, respectively, which are 2.5 and 2 times as large as those pristine SnSe. The charge density distributions reveal that the overlap of wave function has significant change due to the changed bond lengths and bond angles under different strain, which lead to the change of band gap and band dispersion. Our work provides a new effective strategy to enhance the thermoelectric properties of materials.

  7. Modeling L2,3-Edge X-ray Absorption Spectroscopy with Real-Time Exact Two-Component Relativistic Time-Dependent Density Functional Theory.

    Science.gov (United States)

    Kasper, Joseph M; Lestrange, Patrick J; Stetina, Torin F; Li, Xiaosong

    2018-04-10

    X-ray absorption spectroscopy is a powerful technique to probe local electronic and nuclear structure. There has been extensive theoretical work modeling K-edge spectra from first principles. However, modeling L-edge spectra directly with density functional theory poses a unique challenge requiring further study. Spin-orbit coupling must be included in the model, and a noncollinear density functional theory is required. Using the real-time exact two-component method, we are able to variationally include one-electron spin-orbit coupling terms when calculating the absorption spectrum. The abilities of different basis sets and density functionals to model spectra for both closed- and open-shell systems are investigated using SiCl 4 and three transition metal complexes, TiCl 4 , CrO 2 Cl 2 , and [FeCl 6 ] 3- . Although we are working in the real-time framework, individual molecular orbital transitions can still be recovered by projecting the density onto the ground state molecular orbital space and separating contributions to the time evolving dipole moment.

  8. Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.

    Science.gov (United States)

    Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil

    2017-12-13

    Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.

  9. A first principles investigation of the electronic structure of actinide oxides

    DEFF Research Database (Denmark)

    Petit, Leon; Svane, Axel; Szotek, Zdzislawa

    2010-01-01

    The ground state electronic structures of the actinide oxides AO, A2O3 and AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles calculations using the selfinteraction corrected local spin-density approximation. Our study reveals a strong link between preferred oxidation number...... and degree of localization. The ionic nature of the actinide oxides emerges from the fact that those oxides where the ground state is calculated to be metallic do not exist in nature, as the corresponding delocalized f-states favour the accommodation of additional O atoms into the crystal lattice....

  10. Effect of contact deformation on contact electrification: a first-principles calculation

    International Nuclear Information System (INIS)

    Zhang, Yuanyue; Shao, Tianmin

    2013-01-01

    The effect of contact deformation on contact electrification of metallic materials was studied by the first-principles method. The results of charge population and the densities of states of the deformed contact models demonstrated that the magnitude of the transferred charge increased with deformation. The mechanism of the effect of deformation was investigated by studying the electronic properties of the deformed surface slabs. The results showed that crystal deformation led to a change in the electrostatic potential of the metal, where the number of nearly free electrons and unoccupied orbitals for charge transfer increased, and their energy barrier decreased. (paper)

  11. First-principles calculations of mobility

    Science.gov (United States)

    Krishnaswamy, Karthik

    First-principles calculations can be a powerful predictive tool for studying, modeling and understanding the fundamental scattering mechanisms impacting carrier transport in materials. In the past, calculations have provided important qualitative insights, but numerical accuracy has been limited due to computational challenges. In this talk, we will discuss some of the challenges involved in calculating electron-phonon scattering and carrier mobility, and outline approaches to overcome them. Topics will include the limitations of models for electron-phonon interaction, the importance of grid sampling, and the use of Gaussian smearing to replace energy-conserving delta functions. Using prototypical examples of oxides that are of technological importance-SrTiO3, BaSnO3, Ga2O3, and WO3-we will demonstrate computational approaches to overcome these challenges and improve the accuracy. One approach that leads to a distinct improvement in the accuracy is the use of analytic functions for the band dispersion, which allows for an exact solution of the energy-conserving delta function. For select cases, we also discuss direct quantitative comparisons with experimental results. The computational approaches and methodologies discussed in the talk are general and applicable to other materials, and greatly improve the numerical accuracy of the calculated transport properties, such as carrier mobility, conductivity and Seebeck coefficient. This work was performed in collaboration with B. Himmetoglu, Y. Kang, W. Wang, A. Janotti and C. G. Van de Walle, and supported by the LEAST Center, the ONR EXEDE MURI, and NSF.

  12. Band Offsets at the Interface between Crystalline and Amorphous Silicon from First Principles

    Science.gov (United States)

    Jarolimek, K.; Hazrati, E.; de Groot, R. A.; de Wijs, G. A.

    2017-07-01

    The band offsets between crystalline and hydrogenated amorphous silicon (a -Si ∶H ) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015), 10.1063/1.4906195].

  13. Gas adsorption in Mg-porphyrin-based porous organic frameworks: A computational simulation by first-principles derived force field.

    Science.gov (United States)

    Pang, Yujia; Li, Wenliang; Zhang, Jingping

    2017-09-15

    A novel type of porous organic frameworks, based on Mg-porphyrin, with diamond-like topology, named POF-Mgs is computationally designed, and the gas uptakes of CO 2 , H 2 , N 2 , and H 2 O in POF-Mgs are investigated by Grand canonical Monte Carlo simulations based on first-principles derived force fields (FF). The FF, which describes the interactions between POF-Mgs and gases, are fitted by dispersion corrected double-hybrid density functional theory, B2PLYP-D3. The good agreement between the obtained FF and the first-principle energies data confirms the reliability of the FF. Furthermore our simulation shows the presence of a small amount of H 2 O (≤ 0.01 kPa) does not much affect the adsorption quantity of CO 2 , but the presence of higher partial pressure of H 2 O (≥ 0.1 kPa) results in the CO 2 adsorption decrease significantly. The good performance of POF-Mgs in the simulation inspires us to design novel porous materials experimentally for gas adsorption and purification. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  14. Joint density-functional theory and its application to systems in solution

    Science.gov (United States)

    Petrosyan, Sahak A.

    The physics of solvation, the interaction of water with solutes, plays a central role in chemistry and biochemistry, and it is essential for the very existence of life. Despite the central importance of water and the advent of the quantum theory early in the twentieth century, the link between the fundamental laws of physics and the observable properties of water remain poorly understood to this day. The central goal of this thesis is to develop a new formalism and framework to make the study of systems (solutes or surfaces) in contact with liquid water as practical and accurate as standard electronic structure calculations without the need for explicit averaging over large ensembles of configurations of water molecules. The thesis introduces a new form of density functional theory for the ab initio description of electronic systems in contact with a molecular liquid environment. This theory rigorously joins an electron density-functional for the electrons of a solute with a classical density-functional theory for the liquid into a single variational principle for the free energy of the combined system. Using the new form of density-functional theory for the ab initio description of electronic systems in contact with a molecular liquid environment, the thesis then presents the first detailed study of the impact of a solvent on the surface chemistry of Cr2O3, the passivating layer of stainless steel alloys. In comparison to a vacuum, we predict that the presence of water has little impact on the adsorption of chloride ions to the oxygen-terminated surface but has a dramatic effect on the binding of hydrogen to that surface. A key ingredient of a successful joint density functional theory is a good approximate functional for describing the solvent. We explore how the simplest examples of the best known class of approximate forms for the classical density functional fail when applied directly to water. The thesis then presents a computationally efficient density-functional

  15. A first-principles and experimental study of helium diffusion in periclase MgO

    Science.gov (United States)

    Song, Zhewen; Wu, Henry; Shu, Shipeng; Krawczynski, Mike; Van Orman, James; Cherniak, Daniele J.; Bruce Watson, E.; Mukhopadhyay, Sujoy; Morgan, Dane

    2018-02-01

    The distribution of He isotopes is used to trace heterogeneities in the Earth's mantle, and is particularly useful for constraining the length scale of heterogeneity due to the generally rapid diffusivity of helium. However, such an analysis is challenging because He diffusivities are largely unknown in lower mantle phases, which can influence the He profiles in regions that cycle through the lower mantle. With this motivation, we have used first-principles simulations based on density functional theory to study He diffusion in MgO, an important lower mantle phase. We first studied the case of interstitial helium diffusion in perfect MgO and found a migration barrier of 0.73 eV at zero pressure. Then we used the kinetic Monte Carlo method to study the case of substitutional He diffusion in MgO, where we assumed that He diffuses on the cation sublattice through cation vacancies. We also performed experiments on He diffusion at atmospheric pressure using ion implantation and nuclear reaction analysis in both as-received and Ga-doped samples. A comparison between the experimental and simulation results are shown. This work provides a foundation for further studies at high-pressure.

  16. Development of a Knowledge Base of Ti-Alloys From First-Principles and Thermodynamic Modeling

    Science.gov (United States)

    Marker, Cassie

    An aging population with an active lifestyle requires the development of better load-bearing implants, which have high levels of biocompatibility and a low elastic modulus. Titanium alloys, in the body centered cubic phase, are great implant candidates, due to their mechanical properties and biocompatibility. The present work aims at investigating the thermodynamic and elastic properties of bcc Tialloys, using the integrated first-principles based on Density Functional Theory (DFT) and the CALculation of PHAse Diagrams (CALPHAD) method. The use of integrated first-principles calculations based on DFT and CALPHAD modeling has greatly reduced the need for trial and error metallurgy, which is ineffective and costly. The phase stability of Ti-alloys has been shown to greatly affect their elastic properties. Traditionally, CALPHAD modeling has been used to predict the equilibrium phase formation, but in the case of Ti-alloys, predicting the formation of two metastable phases o and alpha" is of great importance as these phases also drastically effect the elastic properties. To build a knowledge base of Ti-alloys, for biomedical load-bearing implants, the Ti-Mo-Nb-Sn-Ta-Zr system was studied because of the biocompatibility and the bcc stabilizing effects of some of the elements. With the focus on bcc Ti-rich alloys, a database of thermodynamic descriptions of each phase for the pure elements, binary and Ti-rich ternary alloys was developed in the present work. Previous thermodynamic descriptions for the pure elements were adopted from the widely used SGTE database for global compatibility. The previous binary and ternary models from the literature were evaluated for accuracy and new thermodynamic descriptions were developed when necessary. The models were evaluated using available experimental data, as well as the enthalpy of formation of the bcc phase obtained from first-principles calculations based on DFT. The thermodynamic descriptions were combined into a database

  17. The problem of the universal density functional and the density matrix functional theory

    International Nuclear Information System (INIS)

    Bobrov, V. B.; Trigger, S. A.

    2013-01-01

    The analysis in this paper shows that the Hohenberg-Kohn theorem is the constellation of two statements: (i) the mathematically rigorous Hohenberg-Kohn lemma, which demonstrates that the same ground-state density cannot correspond to two different potentials of an external field, and (ii) the hypothesis of the existence of the universal density functional. Based on the obtained explicit expression for the nonrel-ativistic particle energy in a local external field, we prove that the energy of the system of more than two non-interacting electrons cannot be a functional of the inhomogeneous density. This result is generalized to the system of interacting electrons. It means that the Hohenberg-Kohn lemma cannot provide justification of the universal density functional for fermions. At the same time, statements of the density functional theory remain valid when considering any number of noninteracting ground-state bosons due to the Bose condensation effect. In the framework of the density matrix functional theory, the hypothesis of the existence of the universal density matrix functional corresponds to the cases of noninteracting particles and to interaction in the Hartree-Fock approximation.

  18. Half-metallicity in a BiFeO3/La2/3Sr1/3MnO3 superlattice: A first-principles study

    KAUST Repository

    Jiwuer, Jilili

    2013-06-01

    We present first-principles results for the electronic, magnetic, and optical properties of the heterostructure as obtained by spin-polarized calculations using density functional theory. The electronic states of the heterostructure are compared to those of the bulk compounds. Structural relaxation turns out to have only a minor impact on the chemical bonding, even though the oxygen octahedra in develop some distortions due to the interface strain. While a small charge transfer affects the heterointerfaces, our results demonstrate that the half-metallic character of is fully maintained. © EPLA, 2013.

  19. First-principle Simulations of Heavy Fermion Materials

    Science.gov (United States)

    Dong, Ruanchen

    Heavy fermion materials, one of the most challenging topics in condensed matter physics, pose a variety of interesting properties and have attracted extensive studies for decades. Although there has been great success in explaining many ground- state properties of solids, the well-known theoretical calculations based on density functional theory (DFT) in its popular local density approximation (LDA) fail to describe heavy fermion materials due to improper treatment of many-body correlation effects. Here with the implementations of dynamical mean-field theory (DMFT) and the Gutzwiller variational method, the computational simulation of the heavy fermion materials is explored further and better compared with experimental data. In this dissertation, first, the theoretical background of DMFT and LDA+G methods is described in detail. The rest is the application of these techniques and is basically divided into two parts. First, the continuous-time quantum Monte Carlo (CT-QMC) method combined with DMFT is used to calculate and compare both the periodic Anderson model (PAM) and the Kondo lattice model (KLM). Different parameter sets of both models are connected by the Schrieffer-Wolff transformation. For spin and orbital degeneracy N = 2 case, a special particle-hole symmetric case of PAM at half-filling which always fixes one electron per impurity site is compared with the results of the KLM. We find a good mapping between PAM and KLM in the limit of large on-site Hubbard interaction U for different properties like self-energy, quasiparticle residue and susceptibility. This allows us to extract quasiparticle mass renormalizations for the f-electrons directly from KLM. The method is further applied to higher degenerate cases and to the realistic heavy fermion system CeRhIn5 in which the estimate of the Sommerfeld coefficient is proven to be close to the experimental value. Second, a series of Cerium based heavy fermion materials is studied using a combination of local

  20. Li-Decorated β12-Borophene as Potential Candidates for Hydrogen Storage: A First-Principle Study.

    Science.gov (United States)

    Liu, Tingting; Chen, Yuhong; Wang, Haifeng; Zhang, Meiling; Yuan, Lihua; Zhang, Cairong

    2017-12-07

    The hydrogen storage properties of pristine β 12 -borophene and Li-decorated β 12 -borophene are systemically investigated by means of first-principles calculations based on density functional theory. The adsorption sites, adsorption energies, electronic structures, and hydrogen storage performance of pristine β 12 -borophene/H₂ and Li- β 12 -borophene/H₂ systems are discussed in detail. The results show that H₂ is dissociated into Two H atoms that are then chemisorbed on β 12 -borophene via strong covalent bonds. Then, we use Li atom to improve the hydrogen storage performance and modify the hydrogen storage capacity of β 12 -borophene. Our numerical calculation shows that Li- β 12 -borophene system can adsorb up to 7 H₂ molecules; while 2Li- β 12 -borophene system can adsorb up to 14 H₂ molecules and the hydrogen storage capacity up to 10.85 wt %.

  1. First-principles calculation of the structural stability of 6d transition metals

    International Nuclear Information System (INIS)

    Oestlin, A.; Vitos, L.

    2011-01-01

    The phase stability of the 6d transition metals (elements 103-111) is investigated using first-principles electronic-structure calculations. Comparison with the lighter transition metals reveals that the structural sequence trend is broken at the end of the 6d series. To account for this anomalous behavior, the effect of relativity on the lattice stability is scrutinized, taking different approximations into consideration. It is found that the mass-velocity and Darwin terms give important contributions to the electronic structure, leading to changes in the interstitial charge density and, thus, in the structural energy difference.

  2. First principles pharmacokinetic modeling: A quantitative study on Cyclosporin

    DEFF Research Database (Denmark)

    Mošat', Andrej; Lueshen, Eric; Heitzig, Martina

    2013-01-01

    renal and hepatic clearances, elimination half-life, and mass transfer coefficients, to establish drug biodistribution dynamics in all organs and tissues. This multi-scale model satisfies first principles and conservation of mass, species and momentum.Prediction of organ drug bioaccumulation...... as a function of cardiac output, physiology, pathology or administration route may be possible with the proposed PBPK framework. Successful application of our model-based drug development method may lead to more efficient preclinical trials, accelerated knowledge gain from animal experiments, and shortened time-to-market...

  3. First-principles study of elastic and thermodynamic properties of orthorhombic OsB4 under high pressure

    Science.gov (United States)

    Yan, Hai-Yan; Zhang, Mei-Guang; Huang, Duo-Hui; Wei, Qun

    2013-04-01

    The first-principles study on the elastic properties, elastic anisotropy and thermodynamic properties of the orthorhombic OsB4 is reported using density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible OsB4 are determined in the pressure range of 0-50 GPa. By the elastic stability criteria, it is predicted that the orthorhombic OsB4 is stable below 50 GPa. By using the quasi-harmonic Debye model, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter of OsB4 are also successfully obtained in the present work.

  4. Monolayer Boron Nitride Substrate Interactions with Graphene Under In-Plane and Perpendicular Strains: A First-Principles Study

    Science.gov (United States)

    Behzad, Somayeh

    2018-04-01

    Effects of strain on the electronic and optical properties of graphene on monolayer boron nitride (BN) substrate are investigated using first-principle calculations based on density functional theory. Strain-free graphene/BN has a small band gap of 97 meV at the K point. The magnitude of band gap increases with in-plane biaxial strain while it decreases with the perpendicular uniaxial strain. The ɛ2 (ω ) spectrum of graphene/BN bilayer for parallel polarization shows red and blue shifts by applying the in-plane tensile and compressive strains, respectively. Also the positions of peaks in the ɛ2 (ω ) spectrum are not significantly changed under perpendicular strain. The calculated results indicate that graphene on the BN substrate has great potential in microelectronic and optoelectronic applications.

  5. Exploring the nucleon structure from first principles of QCD

    Energy Technology Data Exchange (ETDEWEB)

    Bietenholz, W. [Universidad Nacional Autonoma de Mexico (Mexico). Inst. de Ciencias Nucleares; Cundy, N.; Goeckeler, M. [Regensburg Univ. (DE). Inst. fuer Theoretische Physik] (and others)

    2010-04-15

    Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

  6. Exploring the nucleon structure from first principles of QCD

    International Nuclear Information System (INIS)

    Bietenholz, W.; Cundy, N.; Goeckeler, M.

    2010-04-01

    Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

  7. Site specific interaction between ZnO nanoparticles and tyrosine: A density functional theory study

    Science.gov (United States)

    Singh, Satvinder; Singh, Janpreet; Singh, Baljinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

    2018-05-01

    First Principles Calculations have been performed on ZnO/Tyrosine atomic complex to study site specific interaction of Tyrosine and ZnO nanoparticles. Calculated results shows that -COOH group present in Tyrosine is energetically more favorable than -NH2 group. Interactions show ionic bonding between ZnO and Tyrosine. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/Tyrosine complex have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations.

  8. Electron interaction and spin effects in quantum wires, quantum dots and quantum point contacts: a first-principles mean-field approach

    International Nuclear Information System (INIS)

    Zozoulenko, I V; Ihnatsenka, S

    2008-01-01

    We have developed a mean-field first-principles approach for studying electronic and transport properties of low dimensional lateral structures in the integer quantum Hall regime. The electron interactions and spin effects are included within the spin density functional theory in the local density approximation where the conductance, the density, the effective potentials and the band structure are calculated on the basis of the Green's function technique. In this paper we present a systematic review of the major results obtained on the energetics, spin polarization, effective g factor, magnetosubband and edge state structure of split-gate and cleaved-edge overgrown quantum wires as well as on the conductance of quantum point contacts (QPCs) and open quantum dots. In particular, we discuss how the spin-resolved subband structure, the current densities, the confining potentials, as well as the spin polarization of the electron and current densities in quantum wires and antidots evolve when an applied magnetic field varies. We also discuss the role of the electron interaction and spin effects in the conductance of open systems focusing our attention on the 0.7 conductance anomaly in the QPCs. Special emphasis is given to the effect of the electron interaction on the conductance oscillations and their statistics in open quantum dots as well as to interpretation of the related experiments on the ultralow temperature saturation of the coherence time in open dots

  9. Oxygen adsorption and incorporation at irradiated GaN(0001) and GaN(0001¯) surfaces: First-principles density-functional calculations

    Science.gov (United States)

    Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan

    2006-11-01

    Density functional theory calculations of oxygen adsorption and incorporation at the polar GaN(0001) and GaN(0001¯) surfaces have been carried out to explain the experimentally observed reduced oxygen concentration in GaN samples grown by molecular beam epitaxy in the presence of high energy (˜10keV) electron beam irradiation [Myers , J. Vac. Sci. Technol. B 18, 2295 (2000)]. Using a model in which the effect of the irradiation is to excite electrons from the valence to the conduction band, we find that both the energy cost of incorporating oxygen impurities in deeper layers and the oxygen adatom diffusion barriers are significantly reduced in the presence of the excitation. The latter effect leads to a higher probability for two O adatoms to recombine and desorb, and thus to a reduced oxygen concentration in the irradiated samples, consistent with experimental observations.

  10. Spin-Density Functionals from Current-Density Functional Theory and Vice Versa: A Road towards New Approximations

    International Nuclear Information System (INIS)

    Capelle, K.; Gross, E.

    1997-01-01

    It is shown that the exchange-correlation functional of spin-density functional theory is identical, on a certain set of densities, with the exchange-correlation functional of current-density functional theory. This rigorous connection is used to construct new approximations of the exchange-correlation functionals. These include a conceptually new generalized-gradient spin-density functional and a nonlocal current-density functional. copyright 1997 The American Physical Society

  11. Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Sissay, Adonay [Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803 (United States); Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803 (United States); Lopata, Kenneth, E-mail: klopata@lsu.edu [Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803 (United States); Center for Computation and Technology, Louisiana State University, Baton Rouge, Louisiana 70803 (United States)

    2016-09-07

    Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.

  12. Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory

    International Nuclear Information System (INIS)

    Sissay, Adonay; Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J.; Lopata, Kenneth

    2016-01-01

    Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.

  13. Tunable hydrogen separation in porous graphene membrane: first-principle and molecular dynamic simulation.

    Science.gov (United States)

    Tao, Yehan; Xue, Qingzhong; Liu, Zilong; Shan, Meixia; Ling, Cuicui; Wu, Tiantian; Li, Xiaofang

    2014-06-11

    First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 Å) is expected to show high selectivity of H2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H2 over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES1 membranes both exhibit high selectivity for H2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.

  14. Density-functional formulation of the generalized pseudopotential theory. III. Transition-metal interatomic potentials

    Science.gov (United States)

    Moriarty, John A.

    1988-08-01

    The first-principles, density-functional version of the generalized pseudopotential theory (GPT) developed in papers I and II of this series [Phys. Rev. B 16, 2537 (1977); 26, 1754 (1982)] for empty- and filled-d-band metals is here extended to pure transition metals with partially filled d bands. The present focus is on a rigorous, real-space expansion of the bulk total energy in terms of widely transferable, structure-independent interatomic potentials, including both central-force pair interactions and angular-force triplet and quadruplet interactions. To accomplish this expansion, a specialized set of starting equations is derived from the basic local-density formalism for a pure metal, including refined expansions for the exchange-correlation terms and a simplified yet accurate representation of the cohesive energy. The parent pseudo-Green's-function formalism of the GPT is then used to develop these equations in a plane-wave, localized-d-state basis. In this basis, the cohesive energy divides quite naturally into a large volume component and a smaller structural component. The volume component,which includes all one-ion intra-atomic energy contributions, already gives a good description of the cohesion in lowest order. The structural component is expanded in terms of weak interatomic matrix elements and gives rise to a multi-ion series which establishes the interatomic potentials. Special attention is focused on the dominant d-electron contributions to this series and complete formal results for the two-ion, three-ion, and four-ion d-state potentials (vd2, vd3, and vd4) are derived. In addition, a simplified model is used to demonstrate that while vd3 can be of comparable importance to vd2, vd4 is inherently small and the series is rapidly convergent beyond three-ion interactions. Analytic model forms are also derived for vd2 and vd3 in the case of canonical d bands. In this limit, vd2 is purely attractive and varies with interatomic distance as r-10, while

  15. Laboratory Density Functionals

    OpenAIRE

    Giraud, B. G.

    2007-01-01

    We compare several definitions of the density of a self-bound system, such as a nucleus, in relation with its center-of-mass zero-point motion. A trivial deconvolution relates the internal density to the density defined in the laboratory frame. This result is useful for the practical definition of density functionals.

  16. A first-principles study of the SCN− chemisorption on the surface of AlN, AlP, and BP nanotubes

    International Nuclear Information System (INIS)

    Soltani, Alireza; Taghartapeh, Mohammad Ramezani; Mighani, Hossein; Pahlevani, Amin Allah; Mashkoor, Reza

    2012-01-01

    Graphical abstract: Adsorption properties of SCN − on AlN, AlP, and BP nanotubes based on density functional theory. ▶ We demonstrate the most stable configurations (N-side) of SCN − on AlN, AlP, and BP nanotubes models. Highlights: ► The SCN − Adsorption on surface of AlN, AlP, and BP nanotubes were studied via density functional theory (DFT). ► The interaction of SCN − on the electronic properties and the NBO charge distribution of mentioned configurations are investigated. ► The studies suggest that the adsorption energies of SCN − on AlPNT is most notable in comparison with AlNNT and BPNT. - Abstract: We have performed first-principles calculations to explore the adsorption behavior of the SCN − on electronic properties of AlN, AlP, and BP nanotubes. The adsorption value of SCN − for the most stable formation on the AlPNT is about −318.16 kJ mol −1 , which is reason via the chemisorptions of SCN anion. The computed density of states (DOS) indicates that a notable orbital hybridization take place between SCN − and AlP nanotube in adsorption process. Finally, the AlP nanotube can be used to design as useful sensor for nanodevice applications.

  17. Density functional theory for polymeric systems in 2D

    International Nuclear Information System (INIS)

    Słyk, Edyta; Bryk, Paweł; Roth, Roland

    2016-01-01

    We propose density functional theory for polymeric fluids in two dimensions. The approach is based on Wertheim’s first order thermodynamic perturbation theory (TPT) and closely follows density functional theory for polymers proposed by Yu and Wu (2002 J. Chem. Phys . 117 2368). As a simple application we evaluate the density profiles of tangent hard-disk polymers at hard walls. The theoretical predictions are compared against the results of the Monte Carlo simulations. We find that for short chain lengths the theoretical density profiles are in an excellent agreement with the Monte Carlo data. The agreement is less satisfactory for longer chains. The performance of the theory can be improved by recasting the approach using the self-consistent field theory formalism. When the self-avoiding chain statistics is used, the theory yields a marked improvement in the low density limit. Further improvements for long chains could be reached by going beyond the first order of TPT. (paper)

  18. First-principles study on lithium removal from Li{sub 2}MnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Koyama, Yukinori; Tanaka, Isao [Department of Materials Science and Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501 (Japan); Nagao, Miki; Kanno, Ryoji [Department of Electronic Chemistry, Tokyo Institute of Technology, Nagatsuda, Midori, Yokohama 226-8502 (Japan)

    2009-04-01

    A systematic first-principles calculation based on density functional theory is carried out to discuss the redox mechanism of Li{sub 2}MnO{sub 3}. The lattices of structural models having C2/m- and C2/c-type stacking sequences can be regarded as hexagonal, while their symmetry is monoclinic. Different stacking sequences of [Mn{sub 2/3}Li{sub 1/3}] layers do not cause differences in the energy or crystallographic structure, suggesting a disordered stacking sequence. A calculation for Li{sub 2-x}MnO{sub 3} assuming topotactic lithium removal indicates that lithium removal can occur at a potential of about 4.6 V with a wide potential plateau. The electronic structure of Li{sub 2-x}MnO{sub 3} shows that the manganese ions remain in the charge state of Mn{sup 4+} and the charge of the removed lithium ions is compensated by the oxidation of oxygen. (author)

  19. First-principles study of amorphous Ga4Sb6Te3 phase-change alloys

    Science.gov (United States)

    Bouzid, Assil; Gabardi, Silvia; Massobrio, Carlo; Boero, Mauro; Bernasconi, Marco

    2015-05-01

    First-principles molecular dynamics simulations within the density functional theory framework were performed to generate amorphous models of the Ga4Sb6Te3 phase change alloy by quenching from the melt. We find that Ga-Sb and Ga-Te are the most abundant bonds with only a minor amount of Sb-Te bonds participating to the alloy network. Ga and four-coordinated Sb atoms present a tetrahedral-like geometry, whereas three-coordinated Sb atoms are in a pyramidal configuration. The tetrahedral-like geometries are similar to those of the crystalline phase of the two binary compounds GaTe and GaSb. A sizable fraction of Sb-Sb bonds is also present, indicating a partial nanoscale segregation of Sb. Despite the fact that the composition Ga4Sb6Te3 lies on the pseudobinary Ga Sb -Sb2Te3 tie line, the amorphous network can be seen as a mixture of the two binary compounds GaTe and GaSb with intertwined elemental Sb.

  20. Strong interlayer coupling in phosphorene/graphene van der Waals heterostructure: A first-principles investigation

    Science.gov (United States)

    Hu, Xue-Rong; Zheng, Ji-Ming; Ren, Zhao-Yu

    2018-04-01

    Based on first-principles calculations within the framework of density functional theory, we study the electronic properties of phosphorene/graphene heterostructures. Band gaps with different sizes are observed in the heterostructure, and charges transfer from graphene to phosphorene, causing the Fermi level of the heterostructure to shift downward with respect to the Dirac point of graphene. Significantly, strong coupling between two layers is discovered in the band spectrum even though it has a van der Waals heterostructure. A tight-binding Hamiltonian model is used to reveal that the resonance of the Bloch states between the phosphorene and graphene layers in certain K points combines with the symmetry matching between band states, which explains the reason for the strong coupling in such heterostructures. This work may enhance the understanding of interlayer interaction and composition mechanisms in van der Waals heterostructures consisting of two-dimensional layered nanomaterials, and may indicate potential reference information for nanoelectronic and optoelectronic applications.

  1. Half-metallic ferromagnetism in Cu-doped zinc-blende ZnO from first principles study

    International Nuclear Information System (INIS)

    Li, X.F.; Zhang, J.; Xu, B.; Yao, K.L.

    2012-01-01

    Electronic structures and magnetism of Cu-doped zinc-blende ZnO have been investigated by the first-principle method based on density functional theory (DFT). The results show that Cu can induce stable ferromagnetic ground state. The magnetic moment of supercell including single Cu atom is 1.0 μ B . Electronic structure shows that Cu-doped zinc-blende ZnO is a p-type half-metallic ferromagnet. The half-metal property is mainly attribute to the crystal field splitting of Cu 3d orbital, and the ferromagnetism is dominated by the hole-mediated double exchange mechanism. Therefore, Cu-doped zinc-blende ZnO should be useful in semiconductor spintronics and other applications. - Highlights: → Magnetism of Cu-doped zinc-blende ZnO. → Cu-doped zinc-blende ZnO shows interesting half-metal character. → Total energies calculations reveal that Cu can induce ferromagnetic ground state. → Ferromagnetism dominated by the hole-mediated double exchange mechanism.

  2. The interaction of oxygen with TiC(001): Photoemission and first-principles studies

    International Nuclear Information System (INIS)

    Rodriguez, J.A.; Liu, P.; Dvorak, J.; Jirsak, T.; Gomes, J.; Takahashi, Y.; Nakamura, K.

    2004-01-01

    High-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of oxygen with a TiC(001) surface. Atomic oxygen is present on the TiC(001) substrate after small doses of O 2 at room temperature. A big positive shift (1.5-1.8 eV) was detected for the C 1s core level. These photoemission studies suggest the existence of strong O↔C interactions. A phenomenon corroborated by the results of first-principles calculations, which show a CTiTi hollow as the most stable site for the adsorption of O. Ti and C atoms are involved in the adsorption and dissociation of the O 2 molecule. In general, the bond between O and the TiC(001) surface contains a large degree of ionic character. The carbide→O charge transfer is substantial even at high coverages (>0.5 ML) of oxygen. At 500 K and large doses of O 2 , oxidation of the carbide surface occurs with the removal of C and formation of titanium oxides. There is an activation barrier for the exchange of Ti-C and Ti-O bonds which is overcome only by the formation of C-C or C-O bonds on the surface. The mechanism for the removal of a C atom as CO gas involves a minimum of two O adatoms, and three O adatoms are required for the formation of CO 2 gas. Due to the high stability of TiC, an O adatom alone cannot induce the generation of a C vacancy in a flat TiC(001) surface

  3. Next generation extended Lagrangian first principles molecular dynamics.

    Science.gov (United States)

    Niklasson, Anders M N

    2017-08-07

    Extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] is formulated for general Hohenberg-Kohn density-functional theory and compared with the extended Lagrangian framework of first principles molecular dynamics by Car and Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]. It is shown how extended Lagrangian Born-Oppenheimer molecular dynamics overcomes several shortcomings of regular, direct Born-Oppenheimer molecular dynamics, while improving or maintaining important features of Car-Parrinello simulations. The accuracy of the electronic degrees of freedom in extended Lagrangian Born-Oppenheimer molecular dynamics, with respect to the exact Born-Oppenheimer solution, is of second-order in the size of the integration time step and of fourth order in the potential energy surface. Improved stability over recent formulations of extended Lagrangian Born-Oppenheimer molecular dynamics is achieved by generalizing the theory to finite temperature ensembles, using fractional occupation numbers in the calculation of the inner-product kernel of the extended harmonic oscillator that appears as a preconditioner in the electronic equations of motion. Material systems that normally exhibit slow self-consistent field convergence can be simulated using integration time steps of the same order as in direct Born-Oppenheimer molecular dynamics, but without the requirement of an iterative, non-linear electronic ground-state optimization prior to the force evaluations and without a systematic drift in the total energy. In combination with proposed low-rank and on the fly updates of the kernel, this formulation provides an efficient and general framework for quantum-based Born-Oppenheimer molecular dynamics simulations.

  4. First-principles calculations of the elastic constants of the cubic, orthorhombic and hexagonal phases of BaF{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Nyawere, P.W.O., E-mail: otienop98@yahoo.ca [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Department of Computing, Kabarak University, P.O. - Private Bag - 20157 Kabarak (Kenya); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Makau, N.W., E-mail: wanimak@yahoo.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Amolo, G.O., E-mail: georgeamolo862@gmail.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya)

    2014-02-01

    All the elastic constants of cubic, orthorhombic and hexagonal phases of BaF{sub 2} have been calculated using first principles methods. We have employed density-functional theory within generalized gradient approximation (GGA) using a plane-wave pseudopotentials method and a plane-wave basis set. The calculated elastic constant values for a cubic phase compare well with recent theoretical and experimental calculations. The bulk modulus derived from the elastic constant calculations of orthorhombic phase of BaF{sub 2} is 94.5 GPa and those of hexagonal phase is 161 GPa. These values are in good agreement with experimental data available. Stability of these phases of BaF{sub 2} is also estimated in different crystallographic directions.

  5. First-principles calculations of the thermodynamic properties of transuranium elements in a molten salt medium

    International Nuclear Information System (INIS)

    Noh, Seunghyo; Kwak, Dohyun; Lee, Juseung; Kang, Joonhee; Han, Byungchan

    2014-01-01

    We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions.

  6. Structure and stacking faults in layered Mg-Zn-Y alloys: A first-principles study

    International Nuclear Information System (INIS)

    Datta, Aditi; Waghmare, U.V.; Ramamurty, U.

    2008-01-01

    We use first-principles density functional theory total energy calculations based on pseudo-potentials and plane-wave basis to assess stability of the periodic structures with different stacking sequences in Mg-Zn-Y alloys. For pure Mg, we find that the 6-layer (6l) structure with the ABACAB stacking is most stable after the lowest energy hcp (2l) structure with ABAB stacking. Addition of 2 at.% Y leads to stabilization of the structure to 6l sequence whereas the addition of 2 at.% Zn makes the 6l energetically comparable to that of the hcp. Stacking fault (SF) on the basal plane of 6l structure is higher in energy than that of the hcp 2l Mg, which further increases upon Y doping and decreases significantly with Zn doping. SF energy surface for the prismatic slip indicates activation of non-basal slip in alloys with a 6l structure. Charge density analysis shows that the 2l and 6l structures are electronically similar which might be a cause for better stability of 6l structure over a 4l sequence or other periodic structures. Thus, in an Mg-Zn-Y alloy, Y stabilizes the long periodicity, while its mechanical properties are further improved due to Zn doping

  7. Analysis of electron-positron momentum spectra of metallic alloys as supported by first-principles calculations

    OpenAIRE

    Folegati, P.; Makkonen, I.; Ferragut, R.; Puska, Martti J.

    2007-01-01

    Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and i...

  8. External field as the functional of inhomogeneous density and the density matrix functional approach

    NARCIS (Netherlands)

    Bobrov, V.B.; Trigger, S.A.; Vlasov, Y.P.

    2012-01-01

    Based on the Hohenberg-Kohn lemma and the hypotheses of the density functional existence for the external-field potential, it is shown that the strict result of the density functional theory is the equation of the external-field potential as the density functional. This result leads to the

  9. High-Order Hamilton's Principle and the Hamilton's Principle of High-Order Lagrangian Function

    International Nuclear Information System (INIS)

    Zhao Hongxia; Ma Shanjun

    2008-01-01

    In this paper, based on the theorem of the high-order velocity energy, integration and variation principle, the high-order Hamilton's principle of general holonomic systems is given. Then, three-order Lagrangian equations and four-order Lagrangian equations are obtained from the high-order Hamilton's principle. Finally, the Hamilton's principle of high-order Lagrangian function is given.

  10. Reliability evaluation of thermophysical properties from first-principles calculations.

    Science.gov (United States)

    Palumbo, Mauro; Fries, Suzana G; Dal Corso, Andrea; Kürmann, Fritz; Hickel, Tilmann; Neugebauer, Jürg

    2014-08-20

    Thermophysical properties, such as heat capacity, bulk modulus and thermal expansion, are of great importance for many technological applications and are traditionally determined experimentally. With the rapid development of computational methods, however, first-principles computed temperature-dependent data are nowadays accessible. We evaluate various computational realizations of such data in comparison to the experimental scatter. The work is focussed on the impact of different first-principles codes (QUANTUM ESPRESSO and VASP), pseudopotentials (ultrasoft and projector augmented wave) as well as phonon determination methods (linear response and direct force constant method) on these properties. Based on the analysis of data for two pure elements, Cr and Ni, consequences for the reliability of temperature-dependent first-principles data in computational thermodynamics are discussed.

  11. First-Principles Study on the Adsorption Properties of Transition-Metal Atoms on CaO(001) Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Byung Deok [University of Seoul, Seoul (Korea, Republic of); Jang, Young-Rok [Incheon National University, Incheon (Korea, Republic of)

    2017-03-15

    By using first-principles electronic-structure calculations based on the density functional theory, we systematically investigated the adsorption properties of transition-metal (TM) adatoms on CaO(001) surfaces. Optimized adsorption structures and energetics of TM adatoms on CaO(001) are reported for various adsorption structures. The results are different from those of TM adatoms on MgO(001). Concomitantly, this suggests different dynamical properties of TM adatoms on CaO(001) surfaces as compared with TM adatoms on MgO(001) surfaces. Also performed was an analysis of the electronic structures of the TM adatoms on CaO(001) by using the energy positions of the adsorbate states with respect to the valence band maximum of CaO. The results are discussed in connection with the charge states of the TM adatoms on doped CaO(001).

  12. Electronic structure and equation of state of Sm2Co17 from first-principles DFT+ U

    Science.gov (United States)

    Huang, Patrick; Butch, Nicholas P.; Jeffries, Jason R.; McCall, Scott K.

    2013-03-01

    Rare-earth intermetallics have important applications as permanent magnet materials, and the rational optimization of their properties would benefit greatly from guidance from ab initio modeling. However, these systems are particularly challenging for current electronic structure methods. Here, we present an ab initio study of the prototype material Sm2Co17 and related compounds, using density functional theory with a Hubbard correction for the Sm 4 f-electrons (DFT+ U method) and ultrasoft pseudopotentials. The Hubbard U parameter is derived from first principles [Cococcioni and de Gironcoli, PRB 71, 035105 (2005)], not fit to experiment. Our calculations are in good agreement with recent photoemission measurements at ambient pressure and the equation of state up to 40 GPa, thus supporting the validity of our DFT+ U model. Prepared by LLNL under Contract DE-AC52-07NA27344.

  13. The structural, elastic, electronic properties and Debye temperature of Ni3Mo under pressure from first-principles

    International Nuclear Information System (INIS)

    Qi, Lei; Jin, Yuchun; Zhao, Yuhong; Yang, Xiaomin; Zhao, Hui; Han, Peide

    2015-01-01

    Highlights: • Structural, elastic, electronic properties and Debye temperature under pressure. • Higher hardness of Ni 3 Mo compound may be obtained when pressure increases. • Proper pressure can improve the ductility but excess pressure was just the opposite. • Ni 3 Mo compound has no structural phase transformation under pressure up to 30 GPa. • Debye temperatures increase with increasing pressure. - Abstract: With the help of first principles method based on density functional theory, the structural, elastic, electronic properties and Debye temperature of Ni 3 Mo binary compound under pressure are investigated. Our calculated structural parameters are in good agreement with experimental and previous theoretical results. The obtained elastic constants show that Ni 3 Mo compound is mechanically stable. Elastic properties such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio υ are calculated by the Voigt–Reuss–Hill method. The results of B/G under various pressures show that proper pressure can improve the ductility of Ni 3 Mo but excess pressure will make the ductility decrease. In addition, the density of states as a function of pressure is analyzed. The Debye temperature Θ D calculated from elastic constants increases along with the pressure

  14. First-principles calculations of a half-metallic ferromagnet zinc blende Zn1−xVxTe

    International Nuclear Information System (INIS)

    El Amine Monir, M.; Baltache, H.; Khenata, R.; Murtaza, G.; Azam, Sikander; Bouhemadou, A.; Al-Douri, Y.; Bin Omran, S.; Ali, Roshan

    2015-01-01

    First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn 1−x V x Te for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn 1−x V x Te alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C 11 , C 12 and C 44 are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn 0.50 V 0.50 Te and Zn 0.75 V 0.25 Te exhibit a half-metallic character, while Zn 0.25 V 0.75 Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δ x (d) and Δ x (pd) produced by the V(3d)-doped and s(p)–d exchange constants N 0α (conduction band) and N 0β (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µ B and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model. - Highlights: • Some physical properties of Vanadium doped ZnTe have been investigated. • Structural parameters for the parent compounds compare well with the available data. • The elastic and thermal properties are studied for the first time

  15. Structural electronic and mechanical properties of YM2 (M=Mn, Fe, Co) laves phase compounds: First principle calculations analyzed with datamining approach

    Science.gov (United States)

    Saidi, F.; Sebaa, N.; Mahmoudi, A.; Aourag, H.; Merad, G.; Dergal, M.

    2018-06-01

    We performed first-principle calculations to investigate structural, phase stability, electronic and mechanical properties for the Laves phases YM2 (M = Mn, Fe, Co) with C15, C14 and C36 structures. We used the density functional theory within the framework of both pseudo-potentials and plane wave basis using VASP (Vienna Ab Initio Software Package). The calculated equilibrium structural parameters are in accordance with available theoretical values. Mechanical properties were calculated, discussed, and analyzed with data mining approach in terms of structure stability. The results reveal that YCo2 is harder than YFe2 and YMn2.

  16. A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Migaou, Amani; Guiltat, Mathilde; Payen, Kevin; Landa, Georges; Hémeryck, Anne, E-mail: anne.hemeryck@laas.fr [LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse (France); Sarpi, Brice; Daineche, Rachid; Vizzini, Sébastien [Aix Marseille University, IM2NP, Fac Sci St. Jérôme, F-13397 Marseille (France)

    2016-05-21

    First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

  17. Structural, elastic, electronic and dynamical properties of OsB and ReB: Density functional calculations

    Science.gov (United States)

    Li, Yanling; Zeng, Zhi; Lin, Haiqing

    2010-06-01

    The structural, elastic, electronic and dynamical properties of ReB and OsB are investigated by first-principles calculations based on density functional theory. It turns out that ReB and OsB are metallic ultra-incompressible solids with small elastic anisotropy and high hardness. The change of c/ a ratio in OsB indicates that there is a structural phase transition at about 31 GPa. Phonon spectra calculations show that both OsB and ReB are stable dynamically and there are abnormal phonon dispersions along special directions in Brillouin zone. OsB and ReB do not show superconductivity due to very weak electron-phonon interactions in them.

  18. A first principles study

    Indian Academy of Sciences (India)

    We have used density functional theory to obtain the binding curves for a variety of hypothetical periodic structures of Al, Si, Pb, Sn and Au. Upon examining the resulting database of results for equilibrium bond lengths and radial force constants (within a nearest-neighbour model), we find that both decrease smoothly as ...

  19. Magnetism in Sc-doped ZnO with zinc vacancies: A hybrid density functional and GGA + U approaches

    KAUST Repository

    Kanoun, Mohammed; Goumri-Said, Souraya; Schwingenschlö gl, Udo; Manchon, Aurelien

    2012-01-01

    We investigate the zinc vacancy effects on the electronic structures and magnetic properties of Sc-doped ZnO, by performing first-principles calculations within both GGA + U and Heyd-Scuseria-Ernzerhof hybrid functional methods. We find that Sc impurities stabilize considerably Zn vacancies. The electronic and magnetic analysis shows a half metallic ferromagnetic character with a total magnetic moment of 2.01 μ B. The magnetism mainly stems from the O 2p states around the Zn vacancies. Calculations with the hybrid density functional agree with the GGA + U results but give an accurate description of the electronic structure for pure ZnO and Sc-doped ZnO with Zn vacancies. © 2012 Elsevier B.V. All rights reserved.

  20. Magnetism in Sc-doped ZnO with zinc vacancies: A hybrid density functional and GGA + U approaches

    KAUST Repository

    Kanoun, Mohammed

    2012-04-01

    We investigate the zinc vacancy effects on the electronic structures and magnetic properties of Sc-doped ZnO, by performing first-principles calculations within both GGA + U and Heyd-Scuseria-Ernzerhof hybrid functional methods. We find that Sc impurities stabilize considerably Zn vacancies. The electronic and magnetic analysis shows a half metallic ferromagnetic character with a total magnetic moment of 2.01 μ B. The magnetism mainly stems from the O 2p states around the Zn vacancies. Calculations with the hybrid density functional agree with the GGA + U results but give an accurate description of the electronic structure for pure ZnO and Sc-doped ZnO with Zn vacancies. © 2012 Elsevier B.V. All rights reserved.

  1. Theoretical modelling of photoactive molecular systems: insights using the Density Functional Theory

    Energy Technology Data Exchange (ETDEWEB)

    Ciofini, I.; Adamo, C. [Ecole Nationale Superieure de Chimie de Paris, Lab. d' Electrochimie et Chimie Analytique, CNRS UMR 7575, 75 - Paris (France); Laine, Ph.P. [Universite Rene-Descartes, Lab. de Chimie et Biochimie Pharmacologiques et Toxicologiques, CNRS UMR 8601, 75 - Paris (France); Bedioui, F. [Ecole Nationale Superieure de Chimie de Paris, Lab. de Pharmacologie Chimique et Genetique, CNRS FRE 2463 and INSERM U 640, 75 - Paris (France); Daul, C.A. [Fribourg Univ., Dept. de Chimie (Switzerland)

    2006-02-15

    An account of the performance of a modern and efficient approach to Density Functional Theory (DFT) for the prediction of the photophysical behavior of a series of Ru(II) and Os(II) complexes is given. The time-dependent-DFT method was used to interpret their electronic spectra. Two different types of compounds have been analyzed: (1) a complex undergoing a light induced isomerization of one of its coordination bonds; (2) an inorganic dyads expected to undergo intramolecular photoinduced electron transfer to form a charge separated (CS) sate. Besides the noticeable quantitative agreement between computed and experimental absorption spectra, our results allow to clarify, by first principles, both the nature of the excited states and the photochemical behavior of these complex systems, thus underlying the predictive character of the theoretical approach. (authors)

  2. Xenon Defects in Uranium Dioxide From First Principles and Interatomic Potentials

    Science.gov (United States)

    Thompson, Alexander

    In this thesis, we examine the defect energetics and migration energies of xenon atoms in uranium dioxide (UO2) from first principles and interatomic potentials. We also parameterize new, accurate interatomic potentials for xenon and uranium dioxide. To achieve accurate energetics and provide a foundation for subsequent calculations, we address difficulties in finding consistent energetics within Hubbard U corrected density functional theory (DFT+U). We propose a method of slowly ramping the U parameter in order to guide the calculation into low energy orbital occupations. We find that this method is successful for a variety of materials. We then examine the defect energetics of several noble gas atoms in UO2 for several different defect sites. We show that the energy to incorporate large noble gas atoms into interstitial sites is so large that it is energetically favorable for a Schottky defect cluster to be created to relieve the strain. We find that, thermodynamically, xenon will rarely ever be in the interstitial site of UO2. To study larger defects associated with the migration of xenon in UO 2, we turn to interatomic potentials. We benchmark several previously published potentials against DFT+U defect energetics and migration barriers. Using a combination of molecular dynamics and nudged elastic band calculations, we find a new, low energy migration pathway for xenon in UO2. We create a new potential for xenon that yields accurate defect energetics. We fit this new potential with a method we call Iterative Potential Refinement that parameterizes potentials to first principles data via a genetic algorithm. The potential finds accurate energetics for defects with relatively low amounts of strain (xenon in defect clusters). It is important to find accurate energetics for these sorts of low-strain defects because they essentially represent small xenon bubbles. Finally, we parameterize a new UO2 potential that simultaneously yields accurate vibrational properties

  3. Vacancy-induced magnetism in BaTiO3(001) thin films based on density functional theory.

    Science.gov (United States)

    Cao, Dan; Cai, Meng-Qiu; Hu, Wang-Yu; Yu, Ping; Huang, Hai-Tao

    2011-03-14

    The origin of magnetism induced by vacancies on BaTiO(3)(001) surfaces is investigated systematically by first-principles calculations within density-functional theory. The calculated results show that O vacancy is responsible for the magnetism of the BaO-terminated surface and the magnetism of the TiO(2)-terminated surface is induced by Ti vacancy. For the BaO-terminated surface, the magnetism mainly arises from the unpaired electrons that are localized in the O vacancy basin. In contrast, for the TiO(2)-terminated surface, the magnetism mainly originates from the partially occupied O-2p states of the first nearest neighbor O atoms surrounding the Ti vacancy. These results suggest the possibility of implementing magneto-electric coupling in conventional ferroelectric materials.

  4. First Principle simulations of electrochemical interfaces - a DFT study

    DEFF Research Database (Denmark)

    Ahmed, Rizwan

    for the whole system to qualify as a proper electrochemical interface. I have also contributed to the model, which accounts for pH in the first principle electrode-electrolyte interface simulations. This is an important step forward, since electrochemical reaction rate and barrier for charge transfer can......In this thesis, I have looked beyond the computational hydrogen electrode (CHE) model, and focused on the first principle simulations which treats the electrode-electrolyte interfaces explicitly. Since obtaining a realistic electrode-electrolyte interface was difficult, I aimed to address various...... challenges regarding first principle electrochemical interface modeling in order to bridge the gap between the model interface used in simulations and real catalyst at operating conditions. Atomic scale insight for the processes and reactions that occur at the electrochemical interface presents a challenge...

  5. Local-scaling density-functional method: Intraorbit and interorbit density optimizations

    International Nuclear Information System (INIS)

    Koga, T.; Yamamoto, Y.; Ludena, E.V.

    1991-01-01

    The recently proposed local-scaling density-functional theory provides us with a practical method for the direct variational determination of the electron density function ρ(r). The structure of ''orbits,'' which ensures the one-to-one correspondence between the electron density ρ(r) and the N-electron wave function Ψ({r k }), is studied in detail. For the realization of the local-scaling density-functional calculations, procedures for intraorbit and interorbit optimizations of the electron density function are proposed. These procedures are numerically illustrated for the helium atom in its ground state at the beyond-Hartree-Fock level

  6. First-principles investigations on ionization and thermal conductivity of polystyrene for inertial confinement fusion applications

    Energy Technology Data Exchange (ETDEWEB)

    Hu, S. X., E-mail: shu@lle.rochester.edu; Goncharov, V. N.; McCrory, R. L.; Skupsky, S. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Collins, L. A.; Kress, J. D. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2016-04-15

    Using quantum molecular-dynamics (QMD) methods based on the density functional theory, we have performed first-principles investigations of the ionization and thermal conductivity of polystyrene (CH) over a wide range of plasma conditions (ρ = 0.5 to 100 g/cm{sup 3} and T = 15 625 to 500 000 K). The ionization data from orbital-free molecular-dynamics calculations have been fitted with a “Saha-type” model as a function of the CH plasma density and temperature, which gives an increasing ionization as the CH density increases even at low temperatures (T < 50 eV). The orbital-free molecular dynamics method is only used to gauge the average ionization behavior of CH under the average-atom model in conjunction with the pressure-matching mixing rule. The thermal conductivities (κ{sub QMD}) of CH, derived directly from the Kohn–Sham molecular-dynamics calculations, are then analytically fitted with a generalized Coulomb logarithm [(lnΛ){sub QMD}] over a wide range of plasma conditions. When compared with the traditional ionization and thermal conductivity models used in radiation–hydrodynamics codes for inertial confinement fusion simulations, the QMD results show a large difference in the low-temperature regime in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic deuterium–tritium targets with CH ablators on OMEGA and the National Ignition Facility using the QMD-derived ionization and thermal conductivity of CH have predicted ∼20% variation in target performance in terms of hot-spot pressure and neutron yield (gain) with respect to traditional model simulations.

  7. Tuning of electronic band gaps and optoelectronic properties of binary strontium chalcogenides by means of doping of magnesium atom(s)- a first principles based theoretical initiative with mBJ, B3LYP and WC-GGA functionals

    Science.gov (United States)

    Debnath, Bimal; Sarkar, Utpal; Debbarma, Manish; Bhattacharjee, Rahul; Chattopadhyaya, Surya

    2018-02-01

    First principle based theoretical initiative is taken to tune the optoelectronic properties of binary strontium chalcogenide semiconductors by doping magnesium atom(s) into their rock-salt unit cells at specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and such tuning is established by studying structural, electronic and optical properties of designed binary compounds and ternary alloys employing WC-GGA, B3LYP and mBJ exchange-correlation functionals. Band structure of each compound is constructed and respective band gaps under all the potential schemes are measured. The band gap bowing and its microscopic origin are calculated using quadratic fit and Zunger's approach, respectively. The atomic and orbital origins of electronic states in the band structure of any compound are explored from its density of states. The nature of chemical bonds between the constituent atoms in each compound is explored from the valence electron density contour plots. Optical properties of any specimen are explored from the computed spectra of its dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity optical absorption and energy loss function. Several calculated results are compared with available experimental and earlier theoretical data.

  8. First-principles calculations of the electronic structure and optical properties of K1−xNaxTaO3 (x=0, 0.25, 0.5, 0.75, 1)

    International Nuclear Information System (INIS)

    Zhao, Na; Wang, Yue-Hua; Wang, Qing-Xi; Hu, Wen-Jing

    2012-01-01

    The first-principles calculations are performed to investigate the cubic phase composite K 1−x Na x TaO 3 (x=0, 0.25, 0.5, 0.75, 1), by using density functional theory (DFT) with the full potential linearized augmented plane wave (FP-LAPW) method. The energy band structures, density of states (DOS), electron density and optical properties are obtained. The results show that Na ion plays an important role in K 1−x Na x TaO 3 . With the content of Na ion increasing, the changes of lattice parameters, energy gaps, bond lengths and optical properties of K 1−x Na x TaO 3 are regular. Moreover, the dependence of ferroelectric photocatalysis on both optical properties and internal electronic structure are analyzed in detail. It is proposed that the doped materials are promising photocatalytic materials. - Graphical abstract: The density of states (DOS) of K 1−x Na x TaO 3 (x=0.5). Highlights: ► The first-principles calculations are performed, by using DFT with FP-LAPW method. ► The changes of internal electronic structure and optical property of doped materials are regular. ► The dependence of ferroelectric photocatalysis on optical properties is analyzed. ► The dependence of ferroelectric photocatalysis on internal electronic structure is analyzed. ► The doped materials are promising photocatalytic materials.

  9. Defect ordering in aliovalently doped cubic zirconia from first principles

    International Nuclear Information System (INIS)

    Bogicevic, A.; Wolverton, C.; Crosbie, G.M.; Stechel, E.B.

    2001-01-01

    Defect ordering in aliovalently doped cubic-stabilized zirconia is studied using gradient corrected density-functional calculations. Intra- and intersublattice ordering interactions are investigated for both cation (Zr and dopant ions) and anion (oxygen ions and vacancies) species. For yttria-stabilized zirconia, the crystal structure of the experimentally identified, ordered compound δ-Zr 3 Y 4 O 12 is established, and we predict metastable zirconia-rich ordered phases. Anion vacancies repel each other at short separations, but show an energetic tendency to align as third-nearest neighbors along directions. Calculations with divalent (Be, Mg, Ca, Sr, Ba) and trivalent (Y, Sc, B, Al, Ga, In) oxides show that anion vacancies prefer to be close to the smaller of the cations (Zr or dopant ion). When the dopant cation is close in size to Zr, the vacancies show no particular preference, and are thus less prone to be bound preferentially to any particular cation type when the vacancies traverse such oxides. This ordering tendency offers insight into the observed high conductivity of Y 2 O 3 - and Sc 2 O 3 -stabilized zirconia, as well as recent results using, e.g., lanthanide oxides. The calculations point to In 2 O 3 as a particularly promising stabilizer for high ionic conductivity. Thus we are able to directly link (thermodynamic) defect ordering to (kinetic) ionic conductivity in cubic-stabilized zirconia using first-principles atomistic calculations

  10. Fraction of boroxol rings in vitreous boron oxide from a first-principles analysis of Raman and NMR spectra.

    Science.gov (United States)

    Umari, P; Pasquarello, Alfredo

    2005-09-23

    We determine the fraction f of B atoms belonging to boroxol rings in vitreous boron oxide through a first-principles analysis. After generating a model structure of vitreous B2O3 by first-principles molecular dynamics, we address a large set of properties, including the neutron structure factor, the neutron density of vibrational states, the infrared spectra, the Raman spectra, and the 11B NMR spectra, and find overall good agreement with corresponding experimental data. From the analysis of Raman and 11B NMR spectra, we yield consistently for both probes a fraction f of approximately 0.75. This result indicates that the structure of vitreous boron oxide is largely dominated by boroxol rings.

  11. Optoelectronic behavior of Quaternary Uranium Chalcogenides Rb{sub 2}Pd{sub 3}UM{sub 6} (M = S, Se): A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Din, Haleem Ud [Department of Physics, Hazara University, Mansehra (Pakistan); Azam, Sikander; Khan, Saleem Ayaz [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, Mascara 29000 (Algeria)

    2014-12-05

    Highlights: • The Fermi surface and optoelectronic properties for Rb{sub 2}Pd{sub 3}UM{sub 6} (M = S, Se) compounds are investigated for the first time. • The electronic band structure calculations reveal a metallic nature for the herein studied compounds. • The bonding nature between different atoms is discussed. • Considerable anisotropy was found between the principal complex tensor components for the two compounds. - Abstract: First principle calculations of electronic, Fermi surface, electronic charge density and optical properties of Quaternary Uranium Chalcogenides Rb{sub 2}Pd{sub 3}UM{sub 6} (M = S, Se) are performed using full potential linear augmented plane wave (FP-LAPW) method within the frame work of density functional theory. Using mBJ method, the electronic band curves overlap at Fermi level and show metallic band structure for both compounds. The calculated densities of states (DOS) spectra show that the valence band is mainly attributed to Rb-p, Pd-d and S-s/p or Se-s/p states; conduction band is mainly attributed to Pd-d, U-f and S-p or Se-p/d states. From the electronic charge density spectrum, it is revealed that a strong covalent bond exists between Pd and S, and Pd or Se while charge transfer between U and S, U and Se, Rb and S, and Rb and Se atoms results in ionic bond nature. It is noted from Fermi surface calculations that both compounds comprise same number of fast velocity electrons but differs in slow or intermediate velocity of electrons. The calculated frequency dependent dielectric function, energy loss function and reflectivity show a considerable anisotropy for both compounds.

  12. Photoexcitation and Photochemical Stability of Organic Photovoltaic Materials from First Principles

    Science.gov (United States)

    Sai, Na; Leung, Kevin

    2013-03-01

    The development of high efficiency organic photovoltaics (OPV) has recently become enabled by the synthesis of new conjugated polymers with low band gap that allow light absorption over a broader range of the spectrum. Stability of these new polymers, a key requirement for commercialization, has not yet received sufficient attention. Here, we report first-principles theoretical modeling of photo-induced degradation of OPV polymers carried out using ab-initio density functional theory (DFT). We report photooxidation routes and reaction products for reactive species including superoxide oxygen anions and hydroxyl groups interacting with the standard workhorse OPV polymer, poly(3-hexyl-thiophene) (P3HT). We discuss theoretical issues and challenges affecting the modeling such reactions in OPV polymers. We also discuss the application of theoretical methods to low-band-gap polymers, and in particular, the effect of the chemical substitution on the photoexcitation properties of these new polymers. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Deparment of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This work is supported by the Energy Frontier Research Center funded by the U.S. DOE Office of Basic Energy Sciences under Award number DE-SC0001091.

  13. Screening based approach and dehydrogenation kinetics for MgH2: Guide to find suitable dopant using first-principles approach.

    Science.gov (United States)

    Kumar, E Mathan; Rajkamal, A; Thapa, Ranjit

    2017-11-14

    First-principles based calculations are performed to investigate the dehydrogenation kinetics considering doping at various layers of MgH 2 (110) surface. Doping at first and second layer of MgH 2 (110) has a significant role in lowering the H 2 desorption (from surface) barrier energy, whereas the doping at third layer has no impact on the barrier energy. Molecular dynamics calculations are also performed to check the bonding strength, clusterization, and system stability. We study in details about the influence of doping on dehydrogenation, considering the screening factors such as formation enthalpy, bulk modulus, and gravimetric density. Screening based approach assist in finding Al and Sc as the best possible dopant in lowering of desorption temperature, while preserving similar gravimetric density and Bulk modulus as of pure MgH 2 system. The electron localization function plot and population analysis illustrate that the bond between Dopant-Hydrogen is mainly covalent, which weaken the Mg-Hydrogen bonds. Overall we observed that Al as dopant is suitable and surface doping can help in lowering the desorption temperature. So layer dependent doping studies can help to find the best possible reversible hydride based hydrogen storage materials.

  14. First principles simulations of antiphase defects on the SP 90{sup 0} partial dislocation in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Valladares, Alexander; Sutton, A P [Materials Modelling Laboratory, Department of Materials, University of Oxford, OX1 3PH (United Kingdom)

    2006-04-19

    We study the structure and energies of formation of antiphase defects on the single period (SP) 90{sup 0} partial dislocation in silicon using a first principles density functional method. We consider two types of antiphase defect, the type first proposed by Hirsch (1980 J. Microsc. 118 3) wholly inside the dislocation core, and another type that lies partly outside the core. Both types are stable and contain one atom which is threefold coordinated. Each of these atoms has a dangling hybrid which lies in a direction perpendicular to the dislocation line on the slip plane. We obtain values of 1.39 {+-} 0.03 eV and 1.41 {+-} 0.03 eV for the average formation energy of single antiphase defects of the inside and outside types, respectively. We have obtained, using a tight binding scheme, band structures corresponding to these two types of defect, and we find both of them to be associated with states in the gap and each dangling hybrid to contain one electron.

  15. Hybrid Density Functional Study of the Local Structures and Energy Levels of CaAl2O4:Ce3.

    Science.gov (United States)

    Lou, Bibo; Jing, Weiguo; Lou, Liren; Zhang, Yongfan; Yin, Min; Duan, Chang-Kui

    2018-05-03

    First-principles calculations were carried out for the electronic structures of Ce 3+ in calcium aluminate phosphors, CaAl 2 O 4 , and their effects on luminescence properties. Hybrid density functional approaches were used to overcome the well-known underestimation of band gaps of conventional density functional approaches and to calculate the energy levels of Ce 3+ ions more accurately. The obtained 4f-5d excitation and emission energies show good consistency with measured values. A detailed energy diagram of all three sites is obtained, which explains qualitatively all of the luminescent phenomena. With the results of energy levels calculated by combining the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06) and the constraint occupancy approach, we are able to construct a configurational coordinate diagram to analyze the processes of capture of a hole or an electron and luminescence. This approach can be applied for systematic high-throughput calculations in predicting Ce 3+ activated luminescent materials with a moderate computing requirement.

  16. A first principles calculations of structural, electronic, magnetic and dynamical properties of mononitrides FeN and CoN

    International Nuclear Information System (INIS)

    Soni, Himadri R.; Mankad, Venu; Gupta, Sanjeev K.; Jha, Prafulla K.

    2012-01-01

    Highlights: ► We present spin dependent bandstructure, structural and magnetic moment of FeN/CoN. ► The PDC, PHDOS, spin effect on phonons suggests ZB is preferred at ambient pressure. ► Spin calculation offers an opportunity to understand the role of spin on phonons. - Abstract: Using first principles density functional theoretical calculations, the present paper reports a systematic nonspin and spin polarized total energy calculations of the lattice dynamical and a number of other properties such as band structure, structural and magnetic moment of two mononitrides FeN and CoN. The phonon dispersion curves and phonon density of states in the case of FeN and CoN have been determined for the first time and discussed. The structural and dynamical calculations suggest that the zinc blende structure is preferred at ambient pressure for both compounds. The rocksalt FeN has a nonzero magnetic moment while for FeN in zinc blende phase, it is either zero or very small. The zinc blende phase for both compounds is nonmagnetic. The spin calculation offers an intensive opportunity to understand the role of spin on the phonon properties of two mononitrides. Majority of the modes are sensitive to the effect of spin due to the modification of lattice constant. In this work we reveal that spin modifies the interionic interactions and local structure and leads to a flexible lattice which can be used for the functional materials design.

  17. Dimensional cosmological principles

    International Nuclear Information System (INIS)

    Chi, L.K.

    1985-01-01

    The dimensional cosmological principles proposed by Wesson require that the density, pressure, and mass of cosmological models be functions of the dimensionless variables which are themselves combinations of the gravitational constant, the speed of light, and the spacetime coordinates. The space coordinate is not the comoving coordinate. In this paper, the dimensional cosmological principle and the dimensional perfect cosmological principle are reformulated by using the comoving coordinate. The dimensional perfect cosmological principle is further modified to allow the possibility that mass creation may occur. Self-similar spacetimes are found to be models obeying the new dimensional cosmological principle

  18. Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Garwood, Tristan [Univ. of New Mexico, Albuquerque, NM (United States). Center for High Technology Materials; Modine, Normand A. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Krishna, S. [Univ. of New Mexico, Albuquerque, NM (United States). Center for High Technology Materials

    2016-12-18

    The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. By developing a procedure to accurately predict band gaps using hybrid density functional theory, it lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structures calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.

  19. First-principle study of nanostructures of functionalized graphene

    Indian Academy of Sciences (India)

    2014-06-04

    Jun 4, 2014 ... gen, the impact of electronegativity on band gap, binding energy and bond length is visible. It is ... Recent theoretical research has also focussed on .... density of states (figure 3 in [25]) are in close agreement with our results.

  20. What Density Functional Theory could do for Quantum Information

    Science.gov (United States)

    Mattsson, Ann

    2015-03-01

    The Hohenberg-Kohn theorem of Density Functional Theory (DFT), and extensions thereof, tells us that all properties of a system of electrons can be determined through their density, which uniquely determines the many-body wave-function. Given access to the appropriate, universal, functionals of the density we would, in theory, be able to determine all observables of any electronic system, without explicit reference to the wave-function. On the other hand, the wave-function is at the core of Quantum Information (QI), with the wave-function of a set of qubits being the central computational resource in a quantum computer. While there is seemingly little overlap between DFT and QI, reliance upon observables form a key connection. Though the time-evolution of the wave-function and associated phase information is fundamental to quantum computation, the initial and final states of a quantum computer are characterized by observables of the system. While observables can be extracted directly from a system's wave-function, DFT tells us that we may be able to intuit a method for extracting them from its density. In this talk, I will review the fundamentals of DFT and how these principles connect to the world of QI. This will range from DFT's utility in the engineering of physical qubits, to the possibility of using it to efficiently (but approximately) simulate Hamiltonians at the logical level. The apparent paradox of describing algorithms based on the quantum mechanical many-body wave-function with a DFT-like theory based on observables will remain a focus throughout. The ultimate goal of this talk is to initiate a dialog about what DFT could do for QI, in theory and in practice. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  1. Design of new metal-free dyes for dye-sensitized solar cells: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Gu, Xiong; Zhou, Le; Li, Yawei [Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871 (China); Sun, Qiang, E-mail: sunqiang@pku.edu.cn [Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871 (China); Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Jena, Puru [Department of Physics, Virginia Commonwealth University, Richmond, VA 23284 (United States)

    2012-08-06

    Five new metal-free dyes with acceptor–π–donor (A–π–D) structure are studied using first-principles calculation based on density functional theory. Benzothiadiazole (BTD) and triphenylamine (TPA) were chosen, respectively, as an acceptor and a donor with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylamino-styryl)-4H-pyran (DCM) as a π linker. The linker was further modified by -CH=CH- resulting in a red-shift with improved absorption spectra caused by the smaller energy gap and the increased orbital hybridization. The designed dyes are found to exhibit wide absorption spectra, high molar extinction coefficients, desirable orbital distributions, and good energy levels alignment, and hence can have potential applications in dye-sensitized solar cells. -- Highlights: ► New metal-free dyes with A–π–D architecture. ► With wide absorption spectra and high molar extinction coefficients. ► With desirable orbital distribution and good energy levels alignment.

  2. Insights into the ammonia synthesis from first-principles

    DEFF Research Database (Denmark)

    Hellmann, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis

    2006-01-01

    -properties, such as apparent activation energies and reaction orders, are calculated from the first-principles model. Our analysis shows that the reaction order of N-2 is unity under all considered conditions, whereas the reaction orders of H-2 and NH3 depend on reaction conditions. (c) 2006 Elsevier B.V. All rights reserved.......A new set of measurements is used to further test a recently published first-principles model for the ammonia (NH3) synthesis on an unpromoted Ru-based catalyst. A direct comparison shows an overall good agreement in NH3 productivity between the model and the experiment. In addition, macro...

  3. Structural and electronic properties of LaPd2As2 superconductor: First-principle calculations

    Science.gov (United States)

    Singh, Birender; Kumar, Pradeep

    2017-05-01

    In present work we have studied electronic and structural properties of superconducting LaPd2As2 compound having collapsed tetragonal structure using first-principle calculations. The band structure calculations show that the LaPd2As2 is metallic consistent with the reported experimental observation, and the density of states plots clearly shows that at the Fermi level major contribution to density of states arises from Pd 4d and As 4p states, unlike the Fe-based superconductors where major contribution at the Fermi level comes from Fe 3d states. The estimated value of electron-phonon coupling is found to be 0.37, which gives the upper bound of superconducting transition temperature of 5K, suggesting the conventional nature of this superconductor.

  4. Multiconfiguration Pair-Density Functional Theory Is Free From Delocalization Error.

    Science.gov (United States)

    Bao, Junwei Lucas; Wang, Ying; He, Xiao; Gagliardi, Laura; Truhlar, Donald G

    2017-11-16

    Delocalization error has been singled out by Yang and co-workers as the dominant error in Kohn-Sham density functional theory (KS-DFT) with conventional approximate functionals. In this Letter, by computing the vertical first ionization energy for well separated He clusters, we show that multiconfiguration pair-density functional theory (MC-PDFT) is free from delocalization error. To put MC-PDFT in perspective, we also compare it with some Kohn-Sham density functionals, including both traditional and modern functionals. Whereas large delocalization errors are almost universal in KS-DFT (the only exception being the very recent corrected functionals of Yang and co-workers), delocalization error is removed by MC-PDFT, which bodes well for its future as a step forward from KS-DFT.

  5. Functional Assessment of Corticospinal Conduction with Transcranial Magnetic Stimulation: Basic Principles

    DEFF Research Database (Denmark)

    Groppa, S.; Peller, M.; Siebner, Hartwig R.

    2010-01-01

    Here we review how transcranial magnetic stimulation (TMS) is used in clinical practice to examine the functional integrity of the fast conducting fibres of the human corticomotor path ways. We first summarise the technical and physiological principles of TMS that are relevant to its clinical use...

  6. Analytic representation for first-principles pseudopotentials

    International Nuclear Information System (INIS)

    Lam, P.K.; Cohen, M.L.; Zunger, A.

    1980-01-01

    The first-principles pseudopotentials developed by Zunger and Cohen are fit with a simple analytic form chosen to model the main physical properties of the potentials. The fitting parameters for the first three rows of the Periodic Table are presented, and the quality of the fit is discussed. The parameters reflect chemical trends of the elements. We find that a minimum of three parameters is required to reproduce the regularities of the Periodic Table. Application of these analytic potentials is also discussed

  7. Wave-function functionals for the density

    International Nuclear Information System (INIS)

    Slamet, Marlina; Pan Xiaoyin; Sahni, Viraht

    2011-01-01

    We extend the idea of the constrained-search variational method for the construction of wave-function functionals ψ[χ] of functions χ. The search is constrained to those functions χ such that ψ[χ] reproduces the density ρ(r) while simultaneously leading to an upper bound to the energy. The functionals are thereby normalized and automatically satisfy the electron-nucleus coalescence condition. The functionals ψ[χ] are also constructed to satisfy the electron-electron coalescence condition. The method is applied to the ground state of the helium atom to construct functionals ψ[χ] that reproduce the density as given by the Kinoshita correlated wave function. The expectation of single-particle operators W=Σ i r i n , n=-2,-1,1,2, W=Σ i δ(r i ) are exact, as must be the case. The expectations of the kinetic energy operator W=-(1/2)Σ i ∇ i 2 , the two-particle operators W=Σ n u n , n=-2,-1,1,2, where u=|r i -r j |, and the energy are accurate. We note that the construction of such functionals ψ[χ] is an application of the Levy-Lieb constrained-search definition of density functional theory. It is thereby possible to rigorously determine which functional ψ[χ] is closer to the true wave function.

  8. Density functional theory

    International Nuclear Information System (INIS)

    Das, M.P.

    1984-07-01

    The state of the art of the density functional formalism (DFT) is reviewed. The theory is quantum statistical in nature; its simplest version is the well-known Thomas-Fermi theory. The DFT is a powerful formalism in which one can treat the effect of interactions in inhomogeneous systems. After some introductory material, the DFT is outlined from the two basic theorems, and various generalizations of the theorems appropriate to several physical situations are pointed out. Next, various approximations to the density functionals are presented and some practical schemes, discussed; the approximations include an electron gas of almost constant density and an electron gas of slowly varying density. Then applications of DFT in various diverse areas of physics (atomic systems, plasmas, liquids, nuclear matter) are mentioned, and its strengths and weaknesses are pointed out. In conclusion, more recent developments of DFT are indicated

  9. Hybrid density functional theory study of Cu(In1−xGaxSe2 band structure for solar cell application

    Directory of Open Access Journals (Sweden)

    Xu-Dong Chen

    2014-08-01

    Full Text Available Cu(In1−xGaxSe2 (CIGS alloy based thin film photovoltaic solar cells have attracted more and more attention due to its large optical absorption coefficient, long term stability, low cost and high efficiency. However, the previous theoretical investigation of this material with first principle calculation cannot fulfill the requirement of experimental development, especially the accurate description of band structure and density of states. In this work, we use first principle calculation based on hybrid density functional theory to investigate the feature of CIGS, with B3LYP applied in the CuIn1−xGaxSe2 stimulation of the band structure and density of states. We report the simulation of the lattice parameter, band gap and chemical composition. The band gaps of CuGaSe2, CuIn0.25Ga0.75Se2, CuIn0.5Ga0.5Se2, CuIn0.75Ga0.25Se2 and CuInSe2 are obtained as 1.568 eV, 1.445 eV, 1.416 eV, 1.275 eV and 1.205 eV according to our calculation, which agree well with the available experimental values. The band structure of CIGS is also in accordance with the current theory.

  10. The Effect of Indium Concentration on the Structure and Properties of Zirconium Based Intermetallics: First-Principles Calculations

    Directory of Open Access Journals (Sweden)

    Fuda Guo

    2016-01-01

    Full Text Available The phase stability, mechanical, electronic, and thermodynamic properties of In-Zr compounds have been explored using the first-principles calculation based on density functional theory (DFT. The calculated formation enthalpies show that these compounds are all thermodynamically stable. Information on electronic structure indicates that they possess metallic characteristics and there is a common hybridization between In-p and Zr-d states near the Fermi level. Elastic properties have been taken into consideration. The calculated results on the ratio of the bulk to shear modulus (B/G validate that InZr3 has the strongest deformation resistance. The increase of indium content results in the breakout of a linear decrease of the bulk modulus and Young’s modulus. The calculated theoretical hardness of α-In3Zr is higher than the other In-Zr compounds.

  11. Martensitic transformation and phase stability of In-doped Ni-Mn-Sn shape memory alloys from first-principles calculations

    International Nuclear Information System (INIS)

    Xiao, H. B.; Yang, C. P.; Wang, R. L.; Luo, X.; Marchenkov, V. V.

    2014-01-01

    The effect of the alloying element Indium (In) on the martensitic transition, magnetic properties, and phase stabilities of Ni 8 Mn 6 Sn 2−x In x shape memory alloys has been investigated using the first-principles pseudopotential plane-wave method based on density functional theory. The energy difference between the austenitic and martensitic phases was found to increase with increasing In content, which implies an enhancement of the martensitic phase transition temperature (T M ). Moreover, the formation energy results indicate that In-doping increases the relative stability of Ni 8 Mn 6 Sn 2−x In x both in austenite and martensite. This results from a reduction in density of states near the Fermi level regions caused by Ni-3d–In-5p hybridization when Sn is replaced by In. The equilibrium equation of state results show that the alloys Ni 8 Mn 6 Sn 2−x In x exhibit an energetically degenerated effect for an In content of x = ∼1.5. This implies the coexistence of antiparallel and parallel configurations in the austenite.

  12. Kinetic-energy density functional: Atoms and shell structure

    International Nuclear Information System (INIS)

    Garcia-Gonzalez, P.; Alvarellos, J.E.; Chacon, E.

    1996-01-01

    We present a nonlocal kinetic-energy functional which includes an anisotropic average of the density through a symmetrization procedure. This functional allows a better description of the nonlocal effects of the electron system. The main consequence of the symmetrization is the appearance of a clear shell structure in the atomic density profiles, obtained after the minimization of the total energy. Although previous results with some of the nonlocal kinetic functionals have given incipient structures for heavy atoms, only our functional shows a clear shell structure for most of the atoms. The atomic total energies have a good agreement with the exact calculations. Discussion of the chemical potential and the first ionization potential in atoms is included. The functional is also extended to spin-polarized systems. copyright 1996 The American Physical Society

  13. First-principles studies for the stability of a graphene-like boron layer on CrB2(0001) and MoB2(0001)

    International Nuclear Information System (INIS)

    Qin Na; Liu Shiyu; Li Zhen; Zhao Hui; Wang Sanwu

    2011-01-01

    With extensive first-principles density-functional-theory calculations, we investigate the stability and the atomic and electronic structures of the CrB 2 (0001) and MoB 2 (0001) surfaces, each with two different terminations. It is found that the boron-terminated surface is energetically more favorable over the wide range of thermodynamically allowed chemical potentials than the metal-terminated surface for both CrB 2 (0001) and MoB 2 (0001), suggesting a stable layer of graphene-like boron on the surfaces. Our results also show the similarities and the differences in relaxation and in bonding characteristics between the boron-terminated and metal-terminated surfaces.

  14. Relations among several nuclear and electronic density functional reactivity indexes

    Science.gov (United States)

    Torrent-Sucarrat, Miquel; Luis, Josep M.; Duran, Miquel; Toro-Labbé, Alejandro; Solà, Miquel

    2003-11-01

    An expansion of the energy functional in terms of the total number of electrons and the normal coordinates within the canonical ensemble is presented. A comparison of this expansion with the expansion of the energy in terms of the total number of electrons and the external potential leads to new relations among common density functional reactivity descriptors. The formulas obtained provide explicit links between important quantities related to the chemical reactivity of a system. In particular, the relation between the nuclear and the electronic Fukui functions is recovered. The connection between the derivatives of the electronic energy and the nuclear repulsion energy with respect to the external potential offers a proof for the "Quantum Chemical le Chatelier Principle." Finally, the nuclear linear response function is defined and the relation of this function with the electronic linear response function is given.

  15. Coupling of ab initio density functional theory and molecular dynamics for the multiscale modeling of carbon nanotubes

    International Nuclear Information System (INIS)

    Ng, T Y; Yeak, S H; Liew, K M

    2008-01-01

    A multiscale technique is developed that couples empirical molecular dynamics (MD) and ab initio density functional theory (DFT). An overlap handshaking region between the empirical MD and ab initio DFT regions is formulated and the interaction forces between the carbon atoms are calculated based on the second-generation reactive empirical bond order potential, the long-range Lennard-Jones potential as well as the quantum-mechanical DFT derived forces. A density of point algorithm is also developed to track all interatomic distances in the system, and to activate and establish the DFT and handshaking regions. Through parallel computing, this multiscale method is used here to study the dynamic behavior of single-walled carbon nanotubes (SWCNTs) under asymmetrical axial compression. The detection of sideways buckling due to the asymmetrical axial compression is reported and discussed. It is noted from this study on SWCNTs that the MD results may be stiffer compared to those with electron density considerations, i.e. first-principle ab initio methods

  16. Optical Properties of Gallium-Doped Zinc Oxide—A Low-Loss Plasmonic Material: First-Principles Theory and Experiment

    Directory of Open Access Journals (Sweden)

    Jongbum Kim

    2013-12-01

    Full Text Available Searching for better materials for plasmonic and metamaterial applications is an inverse design problem where theoretical studies are necessary. Using basic models of impurity doping in semiconductors, transparent conducting oxides (TCOs are identified as low-loss plasmonic materials in the near-infrared wavelength range. A more sophisticated theoretical study would help not only to improve the properties of TCOs but also to design further lower-loss materials. In this study, optical functions of one such TCO, gallium-doped zinc oxide (GZO, are studied both experimentally and by first-principles density-functional calculations. Pulsed-laser-deposited GZO films are studied by the x-ray diffraction and generalized spectroscopic ellipsometry. Theoretical studies are performed by the total-energy-minimization method for the equilibrium atomic structure of GZO and random phase approximation with the quasiparticle gap correction. Plasma excitation effects are also included for optical functions. This study identifies mechanisms other than doping, such as alloying effects, that significantly influence the optical properties of GZO films. It also indicates that ultraheavy Ga doping of ZnO results in a new alloy material, rather than just degenerately doped ZnO. This work is the first step to achieve a fundamental understanding of the connection between material, structural, and optical properties of highly doped TCOs to tailor those materials for various plasmonic applications.

  17. A massively-parallel electronic-structure calculations based on real-space density functional theory

    International Nuclear Information System (INIS)

    Iwata, Jun-Ichi; Takahashi, Daisuke; Oshiyama, Atsushi; Boku, Taisuke; Shiraishi, Kenji; Okada, Susumu; Yabana, Kazuhiro

    2010-01-01

    Based on the real-space finite-difference method, we have developed a first-principles density functional program that efficiently performs large-scale calculations on massively-parallel computers. In addition to efficient parallel implementation, we also implemented several computational improvements, substantially reducing the computational costs of O(N 3 ) operations such as the Gram-Schmidt procedure and subspace diagonalization. Using the program on a massively-parallel computer cluster with a theoretical peak performance of several TFLOPS, we perform electronic-structure calculations for a system consisting of over 10,000 Si atoms, and obtain a self-consistent electronic-structure in a few hundred hours. We analyze in detail the costs of the program in terms of computation and of inter-node communications to clarify the efficiency, the applicability, and the possibility for further improvements.

  18. Interpretation of monoclinic hafnia valence electron energy-loss spectra by time-dependent density functional theory

    Science.gov (United States)

    Hung, L.; Guedj, C.; Bernier, N.; Blaise, P.; Olevano, V.; Sottile, F.

    2016-04-01

    We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia (m -HfO2) obtained from time-dependent density-functional theory (TDDFT) predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope. Fermi's golden rule density-functional theory (DFT) calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. Using the DFT density of states and TDDFT dielectric functions, we characterize the excitations that result in the m -HfO2 energy-loss spectrum. The sole plasmon occurs between 13 and 16 eV, although the peaks ˜28 and above 40 eV are also due to collective excitations. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons (5 p and 4 f ) on the energy-loss spectrum, and find that the inclusion of transitions from the 4 f band damps the energy-loss intensity in the region above 13 eV. We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation (ALDA) exchange-correlation kernel, as well as from a many-body perspective using "scissors operators" matched to an ab initio G W calculation to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf 4 f shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks.

  19. Applications of Density Functional Theory in Soft Condensed Matter

    Science.gov (United States)

    Löwen, Hartmut

    Applications of classical density functional theory (DFT) to soft matter systems like colloids, liquid crystals and polymer solutions are discussed with a focus on the freezing transition and on nonequilibrium Brownian dynamics. First, after a brief reminder of equilibrium density functional theory, DFT is applied to the freezing transition of liquids into crystalline lattices. In particular, spherical particles with radially symmetric pair potentials will be treated (like hard spheres, the classical one-component plasma or Gaussian-core particles). Second, the DFT will be generalized towards Brownian dynamics in order to tackle nonequilibrium problems. After a general introduction to Brownian dynamics using the complementary Smoluchowski and Langevin pictures appropriate for the dynamics of colloidal suspensions, the dynamical density functional theory (DDFT) will be derived from the Smoluchowski equation. This will be done first for spherical particles (e.g. hard spheres or Gaussian-cores) without hydrodynamic interactions. Then we show how to incorporate hydrodynamic interactions between the colloidal particles into the DDFT framework and compare to Brownian dynamics computer simulations. Third orientational degrees of freedom (rod-like particles) will be considered as well. In the latter case, the stability of intermediate liquid crystalline phases (isotropic, nematic, smectic-A, plastic crystals etc) can be predicted. Finally, the corresponding dynamical extension of density functional theory towards orientational degrees of freedom is proposed and the collective behaviour of "active" (self-propelled) Brownian particles is briefly discussed.

  20. Experimental and density functional study of Mn doped Bi2Te3 topological insulator

    Directory of Open Access Journals (Sweden)

    A. Ghasemi

    2016-12-01

    Full Text Available We present a nanoscale structural and density functional study of the Mn doped 3D topological insulator Bi2Te3. X-ray absorption near edge structure shows that Mn has valency of nominally 2+. Extended x-ray absorption fine structure spectroscopy in combination with electron energy loss spectroscopy (EELS shows that Mn is a substitutional dopant of Bi and Te and also resides in the van der Waals gap between the quintuple layers of Bi2Te3. Combination of aberration-corrected scanning transmission electron microscopy and EELS shows that Mn substitution of Te occurs in film regions with increased Mn concentration. First-principles calculations show that the Mn dopants favor octahedral sites and are ferromagnetically coupled.

  1. A principled dimension-reduction method for the population density approach to modeling networks of neurons with synaptic dynamics.

    Science.gov (United States)

    Ly, Cheng

    2013-10-01

    The population density approach to neural network modeling has been utilized in a variety of contexts. The idea is to group many similar noisy neurons into populations and track the probability density function for each population that encompasses the proportion of neurons with a particular state rather than simulating individual neurons (i.e., Monte Carlo). It is commonly used for both analytic insight and as a time-saving computational tool. The main shortcoming of this method is that when realistic attributes are incorporated in the underlying neuron model, the dimension of the probability density function increases, leading to intractable equations or, at best, computationally intensive simulations. Thus, developing principled dimension-reduction methods is essential for the robustness of these powerful methods. As a more pragmatic tool, it would be of great value for the larger theoretical neuroscience community. For exposition of this method, we consider a single uncoupled population of leaky integrate-and-fire neurons receiving external excitatory synaptic input only. We present a dimension-reduction method that reduces a two-dimensional partial differential-integral equation to a computationally efficient one-dimensional system and gives qualitatively accurate results in both the steady-state and nonequilibrium regimes. The method, termed modified mean-field method, is based entirely on the governing equations and not on any auxiliary variables or parameters, and it does not require fine-tuning. The principles of the modified mean-field method have potential applicability to more realistic (i.e., higher-dimensional) neural networks.

  2. Hydrogenated and halogenated blue phosphorene as Dirac materials: A first principles study

    International Nuclear Information System (INIS)

    Sun, Minglei; Wang, Sake; Yu, Jin; Tang, Wencheng

    2017-01-01

    Highlights: • The fully hydrogenated and halogenated blue phosphorenes are 2D Dirac materials. • The Dirac cone in fluorinated and iodinated blue phosphorenes lies exactly at the Fermi level. • The mass density of hydrogenated and fluorinated blue phosphorenes is rather small. - Abstract: Using first-principles calculations, we systematically investigate the structures and electronic properties of fully hydrogenated and halogenated blue phosphorene (P_2X_2). All these systems possess Dirac cone at high-symmetry K point, which are mainly contributed by P s p_x p_y orbitals. The Dirac cone in P_2F_2 and P_2I_2 systems lies exactly at the Fermi level. Formation energy analysis denotes that all the systems are energetically stable except P_2I_2. The mass density for P_2H_2 and P_2F_2 systems is rather small. Our calculations proposed that these systems, especially P_2F_2 system, have great potential applications in future nanoelectronics.

  3. Identification of the partitioning characteristics of refractory elements in σ and γ phases of Ni-based single crystal superalloys based on first principles

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Fei [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan 250061 (China); Mao, Shengcheng [Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124 (China); Zhang, Jianxin, E-mail: jianxin@sdu.edu.cn [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan 250061 (China)

    2014-10-15

    The impurity formation energies of the σ and γ phases of Ni-based single crystal superalloys doped with W, Cr and Co in different sublattices have been investigated using first-principles based on the density functional theory. The bonding characteristics of the doped σ phase were analyzed with the valence charge densities and the density of the states. The results of the calculations indicated that the typical refractory element W, which has a large atomic size, preferentially partitions into the σ phase due to the nature of the bonding and the unique crystal structure with close-packed planes and large interstitial spaces. In addition, the site preference of refractory elements in γ phase was in the order of W, Cr and Co. - Highlights: • A reasonable σ phase model was adopted in our calculation. • The site preference of refractory elements in σ and γ phases was investigated. • The bonding characteristic was analyzed on the basis of electronic microstructures.

  4. First-Principles Study of Enhanced Magnetoelectric Effects at the Fe/MgO(001) Interface

    Science.gov (United States)

    Niranjan, M. K.; Jaswal, S. S.; Tsymbal, E. Y.; Duan, C.-G.

    2010-03-01

    The magnetoelectric effect allows affecting magnetic properties of materials by electric fields with potential for technological applications such as electrically controlled magnetic data storage. In this study we explore, using first-principles methods, the magnetoelectric effect at the Fe/MgO(001) interface^,1. By explicitly introducing an electric field in our density-functional calculations we demonstrate that the magnetic moment of Fe atoms at the interface changes linearly as a function of the applied electric field with the surface magnetoelectric coefficient being strongly enhanced as compared to that for the clean Fe(001) surface.^1 The effect originates from the increased screening charge associated with a large dielectric constant of MgO. The influence of electric field on relative occupancy of the Fe-3d orbitals leads to significant change in the surface magnetocrystalline anisotropy. These results are compared with the available experimental work.^2 Our results indicate that using high-k dielectrics at the interface with ferromagnetic metals may be very effective in controlling the magnetic properties by electric fields thereby leading to interesting device applications. ^1 C.-G. Duan et al., Phys. Rev. Lett. 101, 137201 (2008). ^2 T. Maruyama et al., Nat. Nanotech., 4, 158 (2009).

  5. Shape-dependent surface magnetism of Co-Pt and Fe-Pt nanoparticles from first principles

    Science.gov (United States)

    Liu, Zhenyu; Wang, Guofeng

    2017-12-01

    In this paper, we have performed the first-principles density functional theory calculations to predict the magnetic properties of the CoPt and FePt nanoparticles in cuboctahedral, decahedral, and icosahedral shapes. The modeled alloy nanoparticles have a diameter of 1.1 nm and consist of 31 5 d Pt atoms and 24 3 d Co (or Fe) atoms. For both CoPt and FePt, we found that the decahedral nanoparticles had appreciably lower surface magnetic moments than the cuboctahedral and icosahedral nanoparticles. Our analysis indicated that this reduction in the surface magnetism was related to a large contraction of atomic spacing and high local Co (or Fe) concentration in the surface of the decahedral nanoparticles. More interestingly, we predicted that the CoPt and FePt cuboctahedral nanoparticles exhibited dramatically different surface spin structures when noncollinear magnetism was taken into account. Our calculation results revealed that surface anisotropy energy decided the fashion of surface spin canting in the CoPt and FePt nanoparticles, confirming previous predictions from atomistic Monte Carlo simulations.

  6. LEGAL PRINCIPLES IN FUNCTION AND PERFORMANCE OF BOT CONTRACT

    Directory of Open Access Journals (Sweden)

    Reifon Cristabella Eventia

    2017-09-01

    Full Text Available Build, Operate and Transfer (BOT represents a long term partnership of the government and private sector. In BOT project, either the government or a private sector identifies a need for a development project. The philosophy in BOT contract begins from the increasing infrastructural needs in all areas and with a limited budget, government are required to commit the duties and functions state governance so that the concept of BOT give a solution through a partnership with the private sector. The government then gives a concession to the private sector to build the project and operate it for a fixed period years, after the period ended, the building shall be transferred to the government. Through BOT, the country is able to gain asset without government spending while maintaining a measure of regulatory control over the project. BOT permits the government to use private sector fund to finance public infrastructure development. The main issues elaborated in this article are the legal principle in the formation of BOT contract and the legal principle in the performance of BOT contract. There are two results; firstly, in the formation of a BOT contract, the principles of partnership and the principle of transparency should be emphasized. Secondly, in performance of the BOT contract, the principle of risk management and the principle of proportionality should be clearly stated in the rules and legal norms.

  7. Magnetism, structures and stabilities of cluster assembled TM@Si nanotubes (TM = Cr, Mn and Fe): a density functional study.

    Science.gov (United States)

    Dhaka, Kapil; Bandyopadhyay, Debashis

    2016-08-02

    The present study reports transition metal (TM = Cr, Mn and Fe) doped silicon nanotubes with tunable band structures and magnetic properties by careful selection of cluster assemblies as building blocks using the first-principles density functional theory. We found that the transition metal doping and in addition, the hydrogen termination process can stabilize the pure silicon nanoclusters or cluster assemblies and then it could be extended as magnetic nanotubes with finite magnetic moments. Study of the band structures and density of states (DOS) of different empty and TM doped nanotubes (Type 1 to Type 4) show that these nanotubes are useful as metals, semiconductors, semi-metals and half-metals. These designer magnetic materials could be useful in spintronics and magnetic devices of nanoscale order.

  8. First-principles surface interaction studies of aluminum-copper and aluminum-copper-magnesium secondary phases in aluminum alloys

    Science.gov (United States)

    da Silva, Thiago H.; Nelson, Eric B.; Williamson, Izaak; Efaw, Corey M.; Sapper, Erik; Hurley, Michael F.; Li, Lan

    2018-05-01

    First-principles density functional theory-based calculations were performed to study θ-phase Al2Cu, S-phase Al2CuMg surface stability, as well as their interactions with water molecules and chloride (Cl-) ions. These secondary phases are commonly found in aluminum-based alloys and are initiation points for localized corrosion. Density functional theory (DFT)-based simulations provide insight into the origins of localized (pitting) corrosion processes of aluminum-based alloys. For both phases studied, Cl- ions cause atomic distortions on the surface layers. The nature of the distortions could be a factor to weaken the interlayer bonds in the Al2Cu and Al2CuMg secondary phases, facilitating the corrosion process. Electronic structure calculations revealed not only electron charge transfer from Cl- ions to alloy surface but also electron sharing, suggesting ionic and covalent bonding features, respectively. The S-phase Al2CuMg structure has a more active surface than the θ-phase Al2Cu. We also found a higher tendency of formation of new species, such as Al3+, Al(OH)2+, HCl, AlCl2+, Al(OH)Cl+, and Cl2 on the S-phase Al2CuMg surface. Surface chemical reactions and resultant species present contribute to establishment of local surface chemistry that influences the corrosion behavior of aluminum alloys.

  9. Arsenene as a promising candidate for NO and NO{sub 2} sensor: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Can [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Liu, Chun-Sheng, E-mail: csliu@njupt.edu.cn [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Yan, Xiaohong [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China)

    2017-03-26

    Based on first-principles calculations, we have studied the adsorption of CO, CO{sub 2}, N{sub 2}, NH{sub 3}, NO and NO{sub 2} molecules on the pristine arsenene monolayer. These gas molecules are held by an interaction that is intermediate between the physisorbed and chemisorbed states. Furthermore, the adsorption of NO and NO{sub 2} can produce a noticeable modifications of the density of states near the Fermi level. Interestingly, only the adsorption of NO and NO{sub 2} can lead to a magnetic moment of 1 μB. Therefore, our results can provide a theoretical basis for the potential applications of arsenene monolayer in gas sensing with electrical and magnetic methods. - Highlights: • A new type of two-dimensional single element semiconductor. • Investigated by first-principles calculations. • Easy desorption and good reversibility. • Gas sensing with electrical and magnetic methods.

  10. Machine learning assisted first-principles calculation of multicomponent solid solutions: estimation of interface energy in Ni-based superalloys

    Science.gov (United States)

    Chandran, Mahesh; Lee, S. C.; Shim, Jae-Hyeok

    2018-02-01

    A disordered configuration of atoms in a multicomponent solid solution presents a computational challenge for first-principles calculations using density functional theory (DFT). The challenge is in identifying the few probable (low energy) configurations from a large configurational space before DFT calculation can be performed. The search for these probable configurations is possible if the configurational energy E({\\boldsymbol{σ }}) can be calculated accurately and rapidly (with a negligibly small computational cost). In this paper, we demonstrate such a possibility by constructing a machine learning (ML) model for E({\\boldsymbol{σ }}) trained with DFT-calculated energies. The feature vector for the ML model is formed by concatenating histograms of pair and triplet (only equilateral triangle) correlation functions, {g}(2)(r) and {g}(3)(r,r,r), respectively. These functions are a quantitative ‘fingerprint’ of the spatial arrangement of atoms, familiar in the field of amorphous materials and liquids. The ML model is used to generate an accurate distribution P(E({\\boldsymbol{σ }})) by rapidly spanning a large number of configurations. The P(E) contains full configurational information of the solid solution and can be selectively sampled to choose a few configurations for targeted DFT calculations. This new framework is employed to estimate (100) interface energy ({σ }{{IE}}) between γ and γ \\prime at 700 °C in Alloy 617, a Ni-based superalloy, with composition reduced to five components. The estimated {σ }{{IE}} ≈ 25.95 mJ m-2 is in good agreement with the value inferred by the precipitation model fit to experimental data. The proposed new ML-based ab initio framework can be applied to calculate the parameters and properties of alloys with any number of components, thus widening the reach of first-principles calculation to realistic compositions of industrially relevant materials and alloys.

  11. Crystal structure of Earth's inner core: A first-principles study

    Science.gov (United States)

    Moustafa, S. G.; Schultz, A. J.; Zurek, E.; Kofke, D. A.

    2017-12-01

    Since the detection of the Earth's solid inner core (IC) by Lehmann in 1936, its composition and crystal structure (which are essential to understand Earth's evolution) have been controversial. While seismological measurements (e.g. PREM) can give a robust estimation of the density, pressure, and elasticity of the IC, they cannot be directly used to determine its composition and/or crystal structure. Experimentally, reaching the extreme IC conditions ( 330 GPa and 6000 K) and getting reliable measurements is very challenging. First-principles calculations provide a viable alternative that can work as a powerful investigative tool. Although several attempts have been made to assess phase stability at IC conditions computationally, they often use a low level of theory for electronic structure (e.g., classical force-field), adopt approximate methods (e.g., quasiharmonic approximation, fixed hcp-c/a), or do not consider finite-size effects. The study of phase stability using accurate first-principles methods is hampered in part by the difficulty of computing the free energy (FE), the central thermodynamic quantity that determines stability, while including anharmonic and finite-size effects. Additional difficulty related to the IC in particular is introduced by the dynamical instability of one of the IC candidate structures (bcc) at low temperature. Recently [1-3], we introduced a novel method (denoted as "harmonically mapped averaging", or HMA) to efficiently measure anharmonic properties (e.g. FE, pressure, elastic modulus) by molecular simulation, yielding orders of magnitude CPU speedup compared to conventional methods. We have applied this method to the hcp candidate phase of iron at the IC conditions, obtaining first-principles anharmonic FE values with unprecedented accuracy and precision [4]. We have now completed and report HMA calculations to assess the phase stability of all IC candidate phases (fcc/hcp/bcc). This knowledge is the prerequisite for

  12. Functional principles of registry-based service discovery

    NARCIS (Netherlands)

    Sundramoorthy, V.; Tan, C.; Hartel, P.H.; Hartog, den J.I.; Scholten, J.

    2005-01-01

    As Service Discovery Protocols (SDP) are becoming increasingly important for ubiquitous computing, they must behave according to predefined principles. We present the functional Principles of Service Discovery for robust, registry-based service discovery. A methodology to guarantee adherence to

  13. Doping and defects in YBa2Cu3O7: Results from hybrid density functional theory

    KAUST Repository

    Schwingenschlö gl, Udo; Schuster, Cosima

    2012-01-01

    7 in two prototypical configurations: Ca doped (hole doping) and O deficient (electron doping). By means of first principles calculations for fully relaxed structures, we evaluate the orbital occupations. We find that the change of the charge density

  14. Multireference Density Functional Theory with Generalized Auxiliary Systems for Ground and Excited States.

    Science.gov (United States)

    Chen, Zehua; Zhang, Du; Jin, Ye; Yang, Yang; Su, Neil Qiang; Yang, Weitao

    2017-09-21

    To describe static correlation, we develop a new approach to density functional theory (DFT), which uses a generalized auxiliary system that is of a different symmetry, such as particle number or spin, from that of the physical system. The total energy of the physical system consists of two parts: the energy of the auxiliary system, which is determined with a chosen density functional approximation (DFA), and the excitation energy from an approximate linear response theory that restores the symmetry to that of the physical system, thus rigorously leading to a multideterminant description of the physical system. The electron density of the physical system is different from that of the auxiliary system and is uniquely determined from the functional derivative of the total energy with respect to the external potential. Our energy functional is thus an implicit functional of the physical system density, but an explicit functional of the auxiliary system density. We show that the total energy minimum and stationary states, describing the ground and excited states of the physical system, can be obtained by a self-consistent optimization with respect to the explicit variable, the generalized Kohn-Sham noninteracting density matrix. We have developed the generalized optimized effective potential method for the self-consistent optimization. Among options of the auxiliary system and the associated linear response theory, reformulated versions of the particle-particle random phase approximation (pp-RPA) and the spin-flip time-dependent density functional theory (SF-TDDFT) are selected for illustration of principle. Numerical results show that our multireference DFT successfully describes static correlation in bond dissociation and double bond rotation.

  15. First-principles Hubbard U approach for small molecule binding in metal-organic frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Mann, Gregory W., E-mail: gmann@berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Mesosphere, Inc., San Francisco, California 94105 (United States); Lee, Kyuho, E-mail: kyuholee@lbl.gov [Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720 (United States); Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Synopsys, Inc., Mountain View, California 94043 (United States); Cococcioni, Matteo, E-mail: matteo.cococcioni@epfl.ch [Theory and Simulation of Materials (THEOS), École Polytechnique Fédérale de Lausanne, Lausanne (Switzerland); Smit, Berend, E-mail: Berend-Smit@berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720 (United States); Laboratory of Molecular Simulation, Institut des Sciences et Ingénierie Chimiques, Valais Ecole Polytechnique Fédérale de Lausanne (EPFL), Rue de l’Industrie 17, CH-1951 Sion (Switzerland); Neaton, Jeffrey B., E-mail: jbneaton@lbl.gov [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States); Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720 (United States)

    2016-05-07

    We apply first-principles approaches with Hubbard U corrections for calculation of small molecule binding energetics to open-shell transition metal atoms in metal-organic frameworks (MOFs). Using density functional theory with van der Waals dispersion-corrected functionals, we determine Hubbard U values ab initio through an established linear response procedure for M-MOF-74, for a number of different metal centers (M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). While our ab initio U values differ from those used in previous work, we show that they result in lattice parameters and electronic contributions to CO{sub 2}-MOF binding energies that lead to excellent agreement with experiments and previous results, yielding lattice parameters within 3%. In addition, U-dependent calculations for an example system, Co-MOF-74, suggest that the CO{sub 2} binding energy grows monotonically with the value of Hubbard U, with the binding energy shifting 4 kJ/mol (or 0.041 eV) over the range of U = 0-5.4 eV. These results provide insight into an approximate but computationally efficient means for calculation of small molecule binding energies to open-shell transition metal atoms in MOFs and suggest that the approach can be predictive with good accuracy, independent of the cations used and the availability of experimental data.

  16. First-principles thermodynamics study of phase stability in inorganic halide perovskite solid solutions

    Science.gov (United States)

    Bechtel, Jonathon S.; Van der Ven, Anton

    2018-04-01

    Halide substitution gives rise to a tunable band gap as a function of composition in halide perovskite materials. However, photoinduced phase segregation, observed at room temperature in mixed halide A Pb (IxBr1-x) 3 systems, limits open circuit voltages and decreases photovoltaic device efficiencies. We investigate equilibrium phase stability of orthorhombic P n m a γ -phase CsM (XxY1-x) 3 perovskites where M is Pb or Sn, and X and Y are Br, Cl, or I. Finite-temperature phase diagrams are constructed using a cluster expansion effective Hamiltonian parameterized from first-principles density-functional-theory calculations. Solid solution phases for CsM (IxBr1-x) 3 and CsM (BrxCl1-x) 3 are predicted to be stable well below room temperature while CsM (IxCl1-x) 3 systems have miscibility gaps that extend above 400 K. The height of the miscibility gap correlates with the difference in volume between end members. Also layered ground states are found on the convex hull at x =2 /3 for CsSnBr2Cl ,CsPbI2Br , and CsPbBrCl2. The impact of these ground states on the finite temperature phase diagram is discussed in the context of the experimentally observed photoinduced phase segregation.

  17. First-principles Hubbard U approach for small molecule binding in metal-organic frameworks

    International Nuclear Information System (INIS)

    Mann, Gregory W.; Lee, Kyuho; Cococcioni, Matteo; Smit, Berend; Neaton, Jeffrey B.

    2016-01-01

    We apply first-principles approaches with Hubbard U corrections for calculation of small molecule binding energetics to open-shell transition metal atoms in metal-organic frameworks (MOFs). Using density functional theory with van der Waals dispersion-corrected functionals, we determine Hubbard U values ab initio through an established linear response procedure for M-MOF-74, for a number of different metal centers (M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). While our ab initio U values differ from those used in previous work, we show that they result in lattice parameters and electronic contributions to CO 2 -MOF binding energies that lead to excellent agreement with experiments and previous results, yielding lattice parameters within 3%. In addition, U-dependent calculations for an example system, Co-MOF-74, suggest that the CO 2 binding energy grows monotonically with the value of Hubbard U, with the binding energy shifting 4 kJ/mol (or 0.041 eV) over the range of U = 0-5.4 eV. These results provide insight into an approximate but computationally efficient means for calculation of small molecule binding energies to open-shell transition metal atoms in MOFs and suggest that the approach can be predictive with good accuracy, independent of the cations used and the availability of experimental data.

  18. A first-principles study of As doping at a disordered Si-SiO2 interface.

    Science.gov (United States)

    Corsetti, Fabiano; Mostofi, Arash A

    2014-02-05

    Understanding the interaction between dopants and semiconductor-oxide interfaces is an increasingly important concern in the drive to further miniaturize modern transistors. To this end, using a combination of first-principles density-functional theory and a continuous random network Monte Carlo method, we investigate electrically active arsenic donors at the interface between silicon and its oxide. Using a realistic model of the disordered interface, we find that a small percentage (on the order of ∼10%) of the atomic sites in the first few monolayers on the silicon side of the interface are energetically favourable for segregation, and that this is controlled by the local bonding and local strain of the defect centre. We also find that there is a long-range quantum confinement effect due to the interface, which results in an energy barrier for dopant segregation, but that this barrier is small in comparison to the effect of the local environment. Finally, we consider the extent to which the energetics of segregation can be controlled by the application of strain to the interface.

  19. First-principles modeling of localized d states with the GW@LDA+U approach

    Science.gov (United States)

    Jiang, Hong; Gomez-Abal, Ricardo I.; Rinke, Patrick; Scheffler, Matthias

    2010-07-01

    First-principles modeling of systems with localized d states is currently a great challenge in condensed-matter physics. Density-functional theory in the standard local-density approximation (LDA) proves to be problematic. This can be partly overcome by including local Hubbard U corrections (LDA+U) but itinerant states are still treated on the LDA level. Many-body perturbation theory in the GW approach offers both a quasiparticle perspective (appropriate for itinerant states) and an exact treatment of exchange (appropriate for localized states), and is therefore promising for these systems. LDA+U has previously been viewed as an approximate GW scheme. We present here a derivation that is simpler and more general, starting from the static Coulomb-hole and screened exchange approximation to the GW self-energy. Following our previous work for f -electron systems [H. Jiang, R. I. Gomez-Abal, P. Rinke, and M. Scheffler, Phys. Rev. Lett. 102, 126403 (2009)10.1103/PhysRevLett.102.126403] we conduct a systematic investigation of the GW method based on LDA+U(GW@LDA+U) , as implemented in our recently developed all-electron GW code FHI-gap (Green’s function with augmented plane waves) for a series of prototypical d -electron systems: (1) ScN with empty d states, (2) ZnS with semicore d states, and (3) late transition-metal oxides (MnO, FeO, CoO, and NiO) with partially occupied d states. We show that for ZnS and ScN, the GW band gaps only weakly depend on U but for the other transition-metal oxides the dependence on U is as strong as in LDA+U . These different trends can be understood in terms of changes in the hybridization and screening. Our work demonstrates that GW@LDA+U with “physical” values of U provides a balanced and accurate description of both localized and itinerant states.

  20. Patching the Exchange-Correlation Potential in Density Functional Theory.

    Science.gov (United States)

    Huang, Chen

    2016-05-10

    A method for directly patching exchange-correlation (XC) potentials in materials is derived. The electron density of a system is partitioned into subsystem densities by dividing its Kohn-Sham (KS) potential among the subsystems. Inside each subsystem, its projected KS potential is required to become the total system's KS potential. This requirement, together with the nearsightedness principle of electronic matters, ensures that the electronic structures inside subsystems can be good approximations to the total system's electronic structure. The nearsightedness principle also ensures that subsystem densities could be well localized in their regions, making it possible to use high-level methods to invert the XC potentials for subsystem densities. Two XC patching methods are developed. In the local XC patching method, the total system's XC potential is improved in the cluster region. We show that the coupling between a cluster and its environment is important for achieving a fast convergence of the electronic structure in the cluster region. In the global XC patching method, we discuss how to patch the subsystem XC potentials to construct the XC potential in the total system, aiming to scale up high-level quantum mechanics simulations of materials. Proof-of-principle examples are given.

  1. Adsorption of methanol molecule on graphene: Experimental results and first-principles calculations

    Science.gov (United States)

    Zhao, X. W.; Tian, Y. L.; Yue, W. W.; Chen, M. N.; Hu, G. C.; Ren, J. F.; Yuan, X. B.

    2018-04-01

    Adsorption properties of methanol molecule on graphene surface are studied both theoretically and experimentally. The adsorption geometrical structures, adsorption energies, band structures, density of states and the effective masses are obtained by means of first-principles calculations. It is found that the electronic characteristics and conductivity of graphene are sensitive to the methanol molecule adsorption. After adsorption of methanol molecule, bandgap appears. With the increasing of the adsorption distance, the bandgap, adsorption energy and effective mass of the adsorption system decreased, hence the resistivity of the system decreases gradually, these results are consistent with the experimental results. All these calculations and experiments indicate that the graphene-based sensors have a wide range of applications in detecting particular molecules.

  2. First principle study on generalized-stacking-fault energy surfaces of B2-AlRE intermetallic compounds

    Science.gov (United States)

    Li, Shaorong; Wang, Shaofeng; Wang, Rui

    2011-12-01

    First-principles calculations are used to predict the generalized-stacking-fault energy (GSFE) surfaces of AlRE intermetallics. The calculations employ the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA) using the density functional theory (DFT). GSFE curves along {1 1 0} direction, {1 1 0} direction and {1 1 0} direction have been calculated. The fitted GSFE surfaces have been obtained from the Fourier series based on the translational symmetry. In order to illuminate the reasonable of our computational accuracy, we have compared our theoretical results of B2 intermetallics YCu with the previous calculated results. The unstable-stacking-fault energy (γus) on the {1 1 0} plane has the laws of AlPr, and directions. For the antiphase boundary (APB) energy, that of AlSc is the lowest in the calculated AlRE intermetallics. So the superdislocation with the Burgers vector along direction of AlSc will easily split into two superpartials.

  3. Phase stability, electronic structure and equation of state of cubic TcN from first-principles calculations

    International Nuclear Information System (INIS)

    Song, T.; Ma, Q.; Sun, X.W.; Liu, Z.J.; Fu, Z.J.; Wei, X.P.; Wang, T.; Tian, J.H.

    2016-01-01

    The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.

  4. Mechanical Properties and Electronic Structure of N and Ta Doped TiC: A First-Principles Study

    International Nuclear Information System (INIS)

    Ma Shi-Qing; Liu Ying; Ye Jin-Wen; Wang Bin

    2014-01-01

    The first principles calculations based on density functional theory (DFT) are employed to investigate the mechanical properties and electronic structure of N and Ta doped TiC. The result shows that the co-doping of nitrogen and tantalum dilates the lattice constant and improves the stability of TiC. Nitrogen and tantalum can signiβcantly enhance the elastic constants and elastic moduli of TiC. The results of B/G and C 12 –C 44 indicate tantalum can markedly increase the ductility of TiC. The electronic structure is calculated to describe the bonding characteristic, which revealed the strong hybridization between C-p and Ta-d and between N-p and Ti-d. The hardnessis is estimated by a semi-empirical model that is based on the Mulliken overlap population and bond length. While the weakest bond takes determinative role of the hardness of materials, the addition of Ta sharply reduces the hardness of TiC. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  5. Density functionals from deep learning

    OpenAIRE

    McMahon, Jeffrey M.

    2016-01-01

    Density-functional theory is a formally exact description of a many-body quantum system in terms of its density; in practice, however, approximations to the universal density functional are required. In this work, a model based on deep learning is developed to approximate this functional. Deep learning allows computational models that are capable of naturally discovering intricate structure in large and/or high-dimensional data sets, with multiple levels of abstraction. As no assumptions are ...

  6. First-principles thermodynamic calculations of diffusion characteristics of impurities in γ-iron

    International Nuclear Information System (INIS)

    Tsuru, T.; Kaji, Y.

    2013-01-01

    Because solute impurities have an effect on embrittlement through segregation under irradiation, solute stability and the influence of irradiation on the diffusion characteristics of impurities become prominent due to several acceleration effects of high irradiance circumstances in irradiated materials. In this study, the diffusion characteristics of several impurities in non-magnetic fcc iron are investigated using first-principles density functional theory (DFT) calculations. In accordance with classical diffusion and transition state theories, we nonempirically evaluated the contribution to properties of the binding energy between vacancy and each impurity and the migration enthalpy. The migration energy was calculated using the nudged elastic band method with DFT. The vacancy formation energy, including the entropic contributions to free energies in γ-iron, was evaluated by considering vibrational phonon frequencies based on frozen phonons employing the harmonic approximation for the lattice dynamics. Consequently, we confirmed that the binding energy between large-radius impurities and vacancies is larger than that with an equivalent size of the solvent element, and that the migration enthalpies of these impurities are quite small compared with self diffusion. This finding may indicate that the electronic binding states at the saddle point have a large influence on the migration of impurities

  7. Density functional study of electronic structure, elastic and optical properties of MNH2 (M=Li, Na, K, Rb)

    International Nuclear Information System (INIS)

    Babu, K Ramesh; Vaitheeswaran, G

    2014-01-01

    We report a systematic first principles density functional study on the electronic structure, elastic and optical properties of nitrogen based solid hydrogen storage materials LiNH 2 , NaNH 2 , KNH 2 , and RbNH 2 . The ground state structural properties are calculated by using standard density functional theory, and also dispersion corrected density functional theory. We find that van der Waals interactions are dominant in LiNH 2 whereas they are relatively weak in other alkali metal amides. The calculated elastic constants show that all the compounds are mechanically stable and LiNH 2 is found to be a stiffer material among the alkali metal amides. The melting temperatures are calculated and follow the order RbNH 2 2 2 2 . The electronic band structure is calculated by using the Tran–Blaha modified Becke–Johnson potential and found that all the compounds are insulators, with a considerable band gap. The [NH 2 ] − derived states completely dominate in the entire valence band region while the metal atom states occupy the conduction band. The calculated band structure is used to analyze the different interband optical transitions occurring between valence and conduction bands. Our calculations show that these materials have considerable optical anisotropy. (paper)

  8. Optical rotation calculated with time-dependent density functional theory: the OR45 benchmark.

    Science.gov (United States)

    Srebro, Monika; Govind, Niranjan; de Jong, Wibe A; Autschbach, Jochen

    2011-10-13

    Time-dependent density functional theory (TDDFT) computations are performed for 42 organic molecules and three transition metal complexes, with experimental molar optical rotations ranging from 2 to 2 × 10(4) deg cm(2) dmol(-1). The performances of the global hybrid functionals B3LYP, PBE0, and BHLYP, and of the range-separated functionals CAM-B3LYP and LC-PBE0 (the latter being fully long-range corrected), are investigated. The performance of different basis sets is studied. When compared to liquid-phase experimental data, the range-separated functionals do, on average, not perform better than B3LYP and PBE0. Median relative deviations between calculations and experiment range from 25 to 29%. A basis set recently proposed for optical rotation calculations (LPol-ds) on average does not give improved results compared to aug-cc-pVDZ in TDDFT calculations with B3LYP. Individual cases are discussed in some detail, among them norbornenone for which the LC-PBE0 functional produced an optical rotation that is close to available data from coupled-cluster calculations, but significantly smaller in magnitude than the liquid-phase experimental value. Range-separated functionals and BHLYP perform well for helicenes and helicene derivatives. Metal complexes pose a challenge to first-principles calculations of optical rotation.

  9. Elastic properties and electronic structure of WS{sub 2} under pressure from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Li, Li [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Civil Aviation Flight Univ. of China, Guanghan (China). Dept. of Physics; Zeng, Zhao-Yi [Chongqing Normal Univ., Chongqing (China). College of Physics and Electronic Engineering; Liang, Ting; Tang, Mei; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics

    2017-07-01

    The influence of pressure on the elastic and mechanical properties of the hexagonal transition-metal dichalcogenide WS{sub 2} is investigated using the first-principles calculations. With the increase in pressure, the lattice parameters and the volume of WS{sub 2} decrease, which is exactly in agreement with the available experimental data and other calculated results. The elastic constants C{sub ij}, bulk modulus B, shear modulus G, Young's modulus E, and Poisson's ratio σ of WS{sub 2} also increase with pressure. At last, for the first time, the band gaps of energy, the partial density of states, and the total density of states under three different pressures are obtained and analysed. It is found that the band gap of WS{sub 2} decreases from 0.843 to 0 eV when the external pressure varies from 0 to 20 GPa, which implies that WS{sub 2} may transform from semiconductors to semimetal phase at a pressure about 20 GPa.

  10. First-principles modeling of titanate/ruthenate superlattices

    Science.gov (United States)

    Junquera, Javier

    2013-03-01

    The possibility to create highly confined two-dimensional electron gases (2DEG) at oxide interfaces has generated much excitement during the last few years. The most widely studied system is the 2DEG formed at the LaO/TiO2 polar interface between LaAlO3 and SrTiO3, where the polar catastrophe at the interface has been invoked as the driving force. More recently, partial or complete delta doping of the Sr or Ti cations at a single layer of a SrTiO3 matrix has also been used to generate 2DEG. Following this recipe, we report first principles characterization of the structural and electronic properties of (SrTiO3)5/(SrRuO3)1 superlattices, where all the Ti of a given layer have been replaced by Ru. We show that the system exhibits a spin-polarized two-dimensional electron gas extremely confined to the 4 d orbitals of Ru in the SrRuO3 layer, a fact that is independent of the level of correlation included in the simulations. For hybrid functionals or LDA+U, every interface in the superlattice behaves as minority-spin half-metal ferromagnet, with a magnetic moment of μ = 2.0 μB/SrRuO3 unit. The shape of the electronic density of states, half metallicity and magnetism are explained in terms of a simplified tight-binding model, considering only the t2 g orbitals plus (i) the bi-dimensionality of the system, and (ii) strong electron correlations. Possible applications are discussed, from their eventual role in thermoelectric applications to the possible tuning of ferromagnetic properties of the 2DEG with the polarization of the dielectric. Work done in collaboration with P. García, M. Verissimo-Alves, D. I. Bilc, and Ph. Ghosez. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes.'' The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the BSC/RES.

  11. Stability, magnetic and electronic properties of cobalt–vacancy defect pairs in graphene: A first-principles study

    International Nuclear Information System (INIS)

    Raji, Abdulrafiu T.; Lombardi, Enrico B.

    2015-01-01

    We report a first-principles investigation of the structural, electronic and magnetic properties of cobalt–vacancy defect complexes in graphene, within the framework of density-functional theory (DFT), incorporating DFT+U. Specifically, we consider the interactions of cobalt and vacancies in graphene, at varying separations and sub-lattices. We show that it is energetically favorable for substitutional Co in graphene to trap an additional vacancy in graphene, forming a Co–vacancy complex. In all the configurations considered, the most stable configuration is when the Co atom is embedded in a divacancy. The magnetic moment induced on the cobalt atom varies as the vacancy–cobalt separation changes, depending not only on the separation, but also on the sub-lattice of the vacancy relative to cobalt. Furthermore, for each separation and sub-lattice considered, the linear density of states of graphene is modified such that Dirac point is either not discernible or has shifted above the Fermi energy. Since individual vacancies or transition metal (TM) atoms, such as cobalt in graphene, have mostly been studied in isolation up to now, ignoring possible transition metal–vacancy interactions, these results have important implications to the fundamental understanding of TM–vacancy defect interactions in graphene

  12. First-principles investigation of mechanical and electronic properties of LaAg5 Laves phase under pressure

    Institute of Scientific and Technical Information of China (English)

    高恩强; 黄福祥; 陈志谦; 王兰兰; 张照超

    2016-01-01

    The effects of applied pressure on the structural, mechanical, and electronic properties of LaAg5 compound were investi-gated employing the first-principles method based on the density functional theory. The mechanical results demonstrated that bulk modulus, shear modulus and Young’s modulus presented the linearly increasing dependences on the external pressure; theB/G and Poisson’s ratio indicated that LaAg5 compound was a ductile material with central forces in interatomic under pressure from 0 to 40 GPa; the universal anisotropic index was performed to investigate the elastic anisotropic of LaAg5. Additionally, the pressure de-pendence of the density of states and Mulliken charge were also discussed. The bonding characterization in LaAg5 was composed of metallic, covalent and ionic. The metallic component was derived from free-electron transferring from Ag-s and Ag-d to Ag-p, and from La-s to La-d. The ionic component was due to the charge movement from La to Ag. The covalent was owing to Ag-p-La-d bonding hybridization and Ag-s-Ag-p in the Ag atomic chains. The covalent and ionic bonds were stronger under pressure but there was no significant change in metallic nature.

  13. Density functional approach for pairing in finite size systems

    International Nuclear Information System (INIS)

    Hupin, G.

    2011-09-01

    The combination of functional theory where the energy is written as a functional of the density, and the configuration mixing method, provides an efficient description of nuclear ground and excited state properties. The specific pathologies that have been recently observed, show the lack of a clear underlying justification associated to the breaking and the restoration of symmetries within density functional theory. This thesis focuses on alternative treatments of pairing correlations in finite many body systems that consider the breaking and the restoration of the particle number conservation. The energy is written as a functional of a projected quasi-particle vacuum and can be linked to the one obtained within the configuration mixing framework. This approach has been applied to make the projection either before or after the application of the variational principle. It is more flexible than the usual configuration mixing method since it can handle more general effective interactions than the latter. The application to the Krypton isotopes shows the feasibility and the efficiency of the method to describe pairing near closed shell nuclei. Following a parallel path, a theory where the energy is written as a functional of the occupation number and natural orbitals is proposed. The new functional is benchmarked in an exactly solvable model, the pairing Hamiltonian. The efficiency and the applicability of the new theory have been tested for various pairing strengths, single particle energy spectra and numbers of particles. (author)

  14. Multipole moments of water molecules in clusters and ice Ih from first principles calculations

    International Nuclear Information System (INIS)

    Batista, E.R.; Xantheas, S.S.; Jonsson, H.

    1999-01-01

    We have calculated molecular multipole moments for water molecules in clusters and in ice Ih by partitioning the charge density obtained from first principles calculations. Various schemes for dividing the electronic charge density among the water molecules were used. They include Bader close-quote s zero flux surfaces and Voronoi partitioning schemes. A comparison was also made with an induction model including dipole, dipole-quadrupole, quadrupole-quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments. We have found that the different density partitioning schemes lead to widely different values for the molecular multipoles, illustrating how poorly defined molecular multipoles are in clusters and condensed environments. For instance, the magnitude of the molecular dipole moment in ice Ih ranges between 2.3 D and 3.1 D depending on the partitioning scheme used. Within each scheme, though, the value for the molecular dipole moment in ice is larger than in the hexamer. The magnitude of the molecular dipole moment in the clusters shows a monotonic increase from the gas phase value to the one in ice Ih, with the molecular dipole moment in the water ring hexamer being smaller than the one in ice Ih for all the partitioning schemes used. copyright 1999 American Institute of Physics

  15. Substitutional Co dopant on the GaAs(110) surface: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Zhou; Yi, Zhijun, E-mail: zhijunyi@cumt.edu.cn

    2016-12-01

    Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and −2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms.

  16. First-principles investigation of optoelectronic and redox properties of (Ta1-xNbx)ON compounds for photocatalysis

    KAUST Repository

    Harb, Moussab

    2015-01-01

    We investigate essential fundamental properties of monoclinic (Ta1-xNbx)ON (x = 0.0625, 0.125, 0.25, and 0.5) solid solution semiconductor materials for water splitting using first-principles computations on the basis of density functional theory (DFT) and density functional perturbation theory (DFPT) using the PBE and HSE06 functionals. The formation energies, band gaps, UV-vis optical absorption coefficients, dielectric constants, charge carrier effective masses, and band edge energy positions of these compounds are evaluated. Similarly to TaON, our calculations reveal strongly 3D delocalized characters of the band edge electronic states through the crystal lattices, high dielectric constants, small hole effective masses along the [001] direction, and small electron effective masses along the [100] direction. This leads to good exciton dissociation ability into free charge carriers, good hole mobility along the [001] direction, and good electron mobility along the [100] direction. The main difference, however, is related to their band edge positions with respect to water redox potentials. TaON with a calculated band gap energy of 3.0 eV is predicted as a good candidate for water oxidation and O2 evolution while the (Ta1-xNbx)ON materials (for 0.25 ≤ x ≤ 0.5) with calculated band gap energies between 2.8 and 2.9 eV reveal suitable band edge positions for water oxidation and H+ reduction. These results offer a grand opportunity for these compounds to be properly synthesized and tested for solar-driven overall water-splitting reactions.

  17. First-principles investigation of optoelectronic and redox properties of (Ta1-xNbx)ON compounds for photocatalysis

    KAUST Repository

    Harb, Moussab

    2015-03-05

    We investigate essential fundamental properties of monoclinic (Ta1-xNbx)ON (x = 0.0625, 0.125, 0.25, and 0.5) solid solution semiconductor materials for water splitting using first-principles computations on the basis of density functional theory (DFT) and density functional perturbation theory (DFPT) using the PBE and HSE06 functionals. The formation energies, band gaps, UV-vis optical absorption coefficients, dielectric constants, charge carrier effective masses, and band edge energy positions of these compounds are evaluated. Similarly to TaON, our calculations reveal strongly 3D delocalized characters of the band edge electronic states through the crystal lattices, high dielectric constants, small hole effective masses along the [001] direction, and small electron effective masses along the [100] direction. This leads to good exciton dissociation ability into free charge carriers, good hole mobility along the [001] direction, and good electron mobility along the [100] direction. The main difference, however, is related to their band edge positions with respect to water redox potentials. TaON with a calculated band gap energy of 3.0 eV is predicted as a good candidate for water oxidation and O2 evolution while the (Ta1-xNbx)ON materials (for 0.25 ≤ x ≤ 0.5) with calculated band gap energies between 2.8 and 2.9 eV reveal suitable band edge positions for water oxidation and H+ reduction. These results offer a grand opportunity for these compounds to be properly synthesized and tested for solar-driven overall water-splitting reactions.

  18. First-principles modeling of hafnia-based nanotubes.

    Science.gov (United States)

    Evarestov, Robert A; Bandura, Andrei V; Porsev, Vitaly V; Kovalenko, Alexey V

    2017-09-15

    Hybrid density functional theory calculations were performed for the first time on structure, stability, phonon frequencies, and thermodynamic functions of hafnia-based single-wall nanotubes. The nanotubes were rolled up from the thin free layers of cubic and tetragonal phases of HfO 2 . It was shown that the most stable HfO 2 single-wall nanotubes can be obtained from hexagonal (111) layer of the cubic phase. Phonon frequencies have been calculated for different HfO 2 nanolayers and nanotubes to prove the local stability and to find the thermal contributions to their thermodynamic functions. The role of phonons in stability of nanotubes seems to be negligible for the internal energy and noticeable for the Helmholtz free energy. Zone folding approach has been applied to estimate the connection between phonon modes of the layer and nanotubes and to approximate the nanotube thermodynamic properties. It is found that the zone-folding approximation is sufficiently accurate for heat capacity, but less accurate for entropy. The comparison has been done between the properties of TiO 2 , ZrO 2 , and HfO 2 . © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  19. First-principles calculation of adsorption of shale gas on CaCO3 (100) surfaces.

    Science.gov (United States)

    Luo, Qiang; Pan, Yikun; Guo, Ping; Wang, Zhouhua; Wei, Na; Sun, Pengfei; Liu, Yuxiao

    2017-06-16

    To demonstrate the adsorption strength of shale gas to calcium carbonate in shale matrix, the adsorption of shale gas on CaCO3 (100) surfaces was studied using the first-principles method, which is based on the density functional theory (DFT). The structures and electronic properties of CH4, C2H6, CO2 and N2 molecules were calculated by the generalized gradient approximation (GGA), for a coverage of 1 monolayer (ML). Under the same conditions, the density of states (DOS) of CaCO3 (100) surfaces before and after the adsorption of shale gas molecules at high-symmetry adsorption sites were compared. The results showed that the adsorption energies of CH4, C2H6, CO2 and N2 on CaCO3 (100) surfaces were between 0.2683 eV and -0.7388 eV. When a CH4 molecule was adsorbed at a hollow site and its 2 hydrogen atoms were parallel to the long diagonal (H3) on the CaCO3 (100) surface, it had the most stable adsorption, and the adsorption energy was only -0.4160 eV. The change of adsorption energy of CH4 was no more than 0.0535 eV. Compared with the DOS distribution of CH4 before adsorption, it shifted to the left overall after adsorption. At the same time, the partial density of states (PDOS) curves of CaCO3 (100) surfaces before and after adsorption basically overlapped. This work showed that the adsorption effect of shale gas on calcium carbonate is very weak, and the adsorption is physisorption at the molecular level.

  20. First-principles thermal conductivity of warm-dense deuterium plasmas for inertial confinement fusion applications.

    Science.gov (United States)

    Hu, S X; Collins, L A; Boehly, T R; Kress, J D; Goncharov, V N; Skupsky, S

    2014-04-01

    Thermal conductivity (κ) of both the ablator materials and deuterium-tritium (DT) fuel plays an important role in understanding and designing inertial confinement fusion (ICF) implosions. The extensively used Spitzer model for thermal conduction in ideal plasmas breaks down for high-density, low-temperature shells that are compressed by shocks and spherical convergence in imploding targets. A variety of thermal-conductivity models have been proposed for ICF hydrodynamic simulations of such coupled and degenerate plasmas. The accuracy of these κ models for DT plasmas has recently been tested against first-principles calculations using the quantum molecular-dynamics (QMD) method; although mainly for high densities (ρ > 100 g/cm3), large discrepancies in κ have been identified for the peak-compression conditions in ICF. To cover the wide range of density-temperature conditions undergone by ICF imploding fuel shells, we have performed QMD calculations of κ for a variety of deuterium densities of ρ = 1.0 to 673.518 g/cm3, at temperatures varying from T = 5 × 103 K to T = 8 × 106 K. The resulting κQMD of deuterium is fitted with a polynomial function of the coupling and degeneracy parameters Γ and θ, which can then be used in hydrodynamic simulation codes. Compared with the "hybrid" Spitzer-Lee-More model currently adopted in our hydrocode lilac, the hydrosimulations using the fitted κQMD have shown up to ∼20% variations in predicting target performance for different ICF implosions on OMEGA and direct-drive-ignition designs for the National Ignition Facility (NIF). The lower the adiabat of an imploding shell, the more variations in predicting target performance using κQMD. Moreover, the use of κQMD also modifies the shock conditions and the density-temperature profiles of the imploding shell at early implosion stage, which predominantly affects the final target performance. This is in contrast to the previous speculation that κQMD changes mainly the

  1. Structural, electronic, elastic and thermal properties of Li{sub 2}AgSb. First-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Li, Ji-Hong [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Longdong Univ., Qingyang (China). College of Physics and Electronic Engineering; Zhu, Xu-Hui [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Sichuan Univ., Chengdu (China). Key Laboratory of High Energy Density Physics and Technology of Ministry of Education; Ji, Guang-Fu [Chinese Academy of Engineering Physics, Mianyang (China). National Key Laboratory of Shock Wave and Detonation Physics

    2015-07-01

    Based on the first-principles density functional theory calculations combined with the quasi-harmonic Debye model, the pressure dependencies of the structural, elastic, electronic and thermal properties of Li{sub 2}AgSb were systematically investigated. The calculated lattice parameters and unit cell volume of Li{sub 2}AgSb at the ground state were in good agreement with the available experimental data. The obtained elastic constants, the bulk modulus and the shear modulus revealed that Li{sub 2}AgSb is mechanically stable and behaves in a ductile manner under the applied pressure. The elasticity-relevant properties, the Young's modulus and the Poisson's ratio showed that pressure can enhance the stiffness of Li{sub 2}AgSb and that Li{sub 2}AgSb is mechanically stable up to 20 GPa. The characteristics of the band structure and the partial density of states of Li{sub 2}AgSb were analysed, showing that Li{sub 2}AgSb is a semiconductor with a direct band gap of 217 meV at 0 GPa and that the increasing pressure can make the band structure of Li{sub 2}AgSb become an indirect one. Studies have shown that, unlike temperature, pressure has little effect on the heat capacity and the thermal expansion coefficient of Li{sub 2}AgSb.

  2. Multicomponent density functional theory embedding formulation

    Energy Technology Data Exchange (ETDEWEB)

    Culpitt, Tanner; Brorsen, Kurt R.; Pak, Michael V.; Hammes-Schiffer, Sharon, E-mail: shs3@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Ave, Urbana, Illinois 61801 (United States)

    2016-07-28

    Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF{sup −} molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.

  3. Effects of adatom and gas molecule adsorption on the physical properties of tellurene: a first principles investigation.

    Science.gov (United States)

    Wang, Xiao Hua; Wang, Da Wei; Yang, Ai Jun; Koratkar, Nikhil; Chu, Ji Feng; Lv, Pin Lei; Rong, Ming Zhe

    2018-02-07

    Tellurene is a new member of the two-dimensional (2D) materials' family, whose existence has been recently confirmed by first principles calculation and experimental work. Tellurene is also the first 2D mono-elemental material of group-VI predicted by scientists, and investigations of its basic properties are still in their infancy. In this study, we use first principles calculation based on density functional theory to investigate the adsorption of nineteen typical adatoms (Li, Na, K, Ca, Fe, Co, Ni, Cu, Zn, Ag, Au, Pd, Pt, B, N, O, Si, Cl, and Al), and five typical gas molecules (H 2 , O 2 , H 2 O, NO 2 , and NH 3 ) on α-phase as well as β-phase tellurene sheets. Our calculations shows that most adatoms are chemisorbed on tellurene sheets with large adsorption energies. Moreover, some of the adatoms are observed to give rise to distinct structural deformations and even local reconstructions. We report that a variety of electronic states are induced by the adatoms, which implies that different electronic structures can be engineered by the adsorption of adatoms. In fact, n-type doping, p-type doping, half-metal, and spin-gapless semiconductor features can be acquired by doping adatoms on tellurene sheets. Our calculations also show that the five gas molecules are all physisorbed on tellurene sheets, and no splitting behaviors are observed. Therefore, the adsorption of the five gas molecules has a weak effect on the electronic properties of tellurene. To conclude, our results indicate that adatom engineering may be used to greatly expand the potential applications of 2D tellurene.

  4. Large negative thermal expansion provided by metal-organic framework MOF-5: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lei, E-mail: leiw@buaa.edu.cn; Wang, Cong, E-mail: congwang@buaa.edu.cn; Sun, Ying; Shi, Kewen; Deng, Sihao; Lu, Huiqing

    2016-06-01

    The thermodynamic properties and negative thermal expansion (NTE) behavior of metal-organic framework MOF-5 are investigated within the quasi-harmonic approximation, by using density functional theory. For nanoporous MOF-5, the temperature dependence of bulk modulus increases with increasing temperature, indicating that the resistance to compression is enhanced gradually. The large NTE behavior is obtained, which agrees reasonably with the experimental data. From the Grüneisen parameter as a function of temperature, it can be found that low-frequency phonons are closely associated with the NTE of MOF-5. The corresponding vibrational modes can be viewed as the results of local deformations (translation, rotation, twisting) of BDC (1,4-benzenedicarboxylate) linker and zinc clusters. The lowest-frequency phonon mode (the transverse motion of carboxylate groups and benzene ring, zinc clusters being as rigid units) is confirmed to be most responsible for thermal contraction. - Highlights: • The related thermodynamic properties and NTE behavior of MOF-5 are investigated by first principles. • Contrary to other inorganic NTE materials, bulk modulus of MOF-5 increases on heating. • The low-frequency phonons are closely associated with the NTE of MOF-5. • The NTE-contributing vibrational modes are elucidated clearly.

  5. Large negative thermal expansion provided by metal-organic framework MOF-5: A first-principles study

    International Nuclear Information System (INIS)

    Wang, Lei; Wang, Cong; Sun, Ying; Shi, Kewen; Deng, Sihao; Lu, Huiqing

    2016-01-01

    The thermodynamic properties and negative thermal expansion (NTE) behavior of metal-organic framework MOF-5 are investigated within the quasi-harmonic approximation, by using density functional theory. For nanoporous MOF-5, the temperature dependence of bulk modulus increases with increasing temperature, indicating that the resistance to compression is enhanced gradually. The large NTE behavior is obtained, which agrees reasonably with the experimental data. From the Grüneisen parameter as a function of temperature, it can be found that low-frequency phonons are closely associated with the NTE of MOF-5. The corresponding vibrational modes can be viewed as the results of local deformations (translation, rotation, twisting) of BDC (1,4-benzenedicarboxylate) linker and zinc clusters. The lowest-frequency phonon mode (the transverse motion of carboxylate groups and benzene ring, zinc clusters being as rigid units) is confirmed to be most responsible for thermal contraction. - Highlights: • The related thermodynamic properties and NTE behavior of MOF-5 are investigated by first principles. • Contrary to other inorganic NTE materials, bulk modulus of MOF-5 increases on heating. • The low-frequency phonons are closely associated with the NTE of MOF-5. • The NTE-contributing vibrational modes are elucidated clearly.

  6. First-principle approach based bandgap engineering for cubic boron nitride doped with group IIA elements

    Science.gov (United States)

    Li, Yubo; Wang, Pengtao; Hua, Fei; Zhan, Shijie; Wang, Xiaozhi; Luo, Jikui; Yang, Hangsheng

    2018-03-01

    Electronic properties of cubic boron nitride (c-BN) doped with group IIA elements were systematically investigated using the first principle calculation based on density functional theory. The electronic bandgap of c-BN was found to be narrowed when the impurity atom substituted either the B (IIA→B) or the N (IIA→N) atom. For IIA→B, a shallow accept level degenerated into valence band (VB); while for IIA→N, a shallow donor level degenerated conduction band (CB). In the cases of IIBe→N and IIMg→N, deep donor levels were also induced. Moreover, a zigzag bandgap narrowing pattern was found, which is in consistent with the variation pattern of dopants' radius of electron occupied outer s-orbital. From the view of formation energy, the substitution of B atom under N-rich conditions and the substitution of N atom under B-rich conditions were energetically favored. Our simulation results suggested that Mg and Ca are good candidates for p-type dopants, and Ca is the best candidate for n-type dopant.

  7. First-principles calculations of orientation dependence of Si thermal oxidation based on Si emission model

    Science.gov (United States)

    Nagura, Takuya; Kawachi, Shingo; Chokawa, Kenta; Shirakawa, Hiroki; Araidai, Masaaki; Kageshima, Hiroyuki; Endoh, Tetsuo; Shiraishi, Kenji

    2018-04-01

    It is expected that the off-state leakage current of MOSFETs can be reduced by employing vertical body channel MOSFETs (V-MOSFETs). However, in fabricating these devices, the structure of the Si pillars sometimes cannot be maintained during oxidation, since Si atoms sometimes disappear from the Si/oxide interface (Si missing). Thus, in this study, we used first-principles calculations based on the density functional theory, and investigated the Si emission behavior at the various interfaces on the basis of the Si emission model including its atomistic structure and dependence on Si crystal orientation. The results show that the order in which Si atoms are more likely to be emitted during thermal oxidation is (111) > (110) > (310) > (100). Moreover, the emission of Si atoms is enhanced as the compressive strain increases. Therefore, the emission of Si atoms occurs more easily in V-MOSFETs than in planar MOSFETs. To reduce Si missing in V-MOSFETs, oxidation processes that induce less strain, such as wet or pyrogenic oxidation, are necessary.

  8. Power probability density function control and performance assessment of a nuclear research reactor

    International Nuclear Information System (INIS)

    Abharian, Amir Esmaeili; Fadaei, Amir Hosein

    2014-01-01

    Highlights: • In this paper, the performance assessment of static PDF control system is discussed. • The reactor PDF model is set up based on the B-spline functions. • Acquaints of Nu, and Th-h. equations solve concurrently by reformed Hansen’s method. • A principle of performance assessment is put forward for the PDF of the NR control. - Abstract: One of the main issues in controlling a system is to keep track of the conditions of the system function. The performance condition of the system should be inspected continuously, to keep the system in reliable working condition. In this study, the nuclear reactor is considered as a complicated system and a principle of performance assessment is used for analyzing the performance of the power probability density function (PDF) of the nuclear research reactor control. First, the model of the power PDF is set up, then the controller is designed to make the power PDF for tracing the given shape, that make the reactor to be a closed-loop system. The operating data of the closed-loop reactor are used to assess the control performance with the performance assessment criteria. The modeling, controller design and the performance assessment of the power PDF are all applied to the control of Tehran Research Reactor (TRR) power in a nuclear process. In this paper, the performance assessment of the static PDF control system is discussed, the efficacy and efficiency of the proposed method are investigated, and finally its reliability is proven

  9. Molecular structures from density functional calculations with simulated annealing

    International Nuclear Information System (INIS)

    Jones, R.O.

    1991-01-01

    The geometrical structure of any aggregate of atoms is one of its basic properties and, in principle, straightforward to predict. One chooses a structure, determines the total energy E of the system of electrons and ions, and repeats the calculation for all possible geometries. The ground state structure is that with the lowest energy. A quantum mechanical calculation of the exact wave function Ψ would lead to the total energy, but this is practicable only in very small molecules. Furthermore, the number of local minima in the energy surface increases dramatically with increasing molecular size. While traditional ab initio methods have had many impressive successes, the difficulties have meant that they have focused on systems with relatively few local minima, or have used experiments or experience to limit the range of geometries studied. On the other hand, calculations for much larger molecules and extended systems are often forced to use simplifying assumptions about the interatomic forces that limit their predictive capability. The approach described here avoids both of these extremes: Total energies of predictive value are calculated without using semi-empirical force laws, and the problem of multiple minima in the energy surface is addressed. The density functional formalism, with a local density approximation for the exchange-correlation energy, allows one to calculate the total energy for a given geometry in an efficient, if approximate, manner. Calculations for heavier elements are not significantly more difficult than for those in the first row and provide an ideal way to study bonding trends. When coupled with finite-temperature molecular dynamics, this formalism can avoid many of the energetically unfavorable minima in the energy surface. We show here that the method leads to surprising and exciting results. (orig.)

  10. Phases of Ca from first principles

    International Nuclear Information System (INIS)

    Qiu, S L; Marcus, P M

    2009-01-01

    Structures and properties of many of the phases of Ca under pressure are calculated from first principles by a systematic procedure that minimizes total energy E with respect to structure under the constraint of constant volume V. The minima of E are followed on successive sweeps of lattice parameters for 11 of 14 Bravais symmetries for one-atom-per-cell structures. The structures include the four orthorhombic phases. Also included are the hexagonal close-packed and cubic diamond phases with two atoms per primitive cell. No uniquely orthorhombic phases are found; all one-atom orthorhombic phases over a mega-bar pressure range are identical to higher-symmetry phases. The simple cubic phase is shown to be stable where it is the ground state. The number of distinct one-atom phases reduces to five plus the two two-atom phases. For each of these phases the Gibbs free energy at pressure p, G(p), is calculated for a non-vibrating lattice; the functions G(p) give the ground state at each p, the relative stabilities of all phases and the thermodynamic phase transition pressures for all phase transitions over a several-megabar range.

  11. Principles of taxation as a means of implementing fiscal function of the tax

    Directory of Open Access Journals (Sweden)

    К. О. Гетьман

    2015-05-01

    of tax legislation Ukraine». It is difficult to unconditionally accept the title of this article. Analyzing in detail the principles set out in the Tax Code of Ukraine, it is easy to conclude that they concern not only the principles of tax law is as following, most general tax regulation principles, the legal nature of tax administration.Dynamic analysis of principles of taxation, which is a particular sense associated with fiscal functions of tax involves comparing the principles embodied today by the current Tax Code of Ukraine and have been regulated by the law of Ukraine "On taxation system". Conventionally, we can distribute them into three blocks: a the principles enshrined in the Tax Code of Ukraine for the first time; b Principles of Tax Code of Ukraine, identified in tax legislation Ukraine to its adoption; c the principles that disappeared with the tax laws of the Tax Code of Ukraine. It is clear that it is only the principles that we can associate with providing fiscal function of the tax. Conclusions.  Proposed distribution and comparison of taxation principles, in one way or another related to the fiscal functions of tax into three blocks: a the principles contained in the Tax Code of Ukraine for the first time; b the principles of the Tax Code of Ukraine, which were identified in the tax legislation of Ukraine and to the adoption; c the principles that have disappeared from the tax legislation with the adoption of the Tax Code of Ukraine.Describing the features of the tax should be based on the effect of the significant leverage in tax regulation. Still another sustained a lively discussion about the number and nature of these functions. According to the author, the most balanced view of the tax system functions can provide three of them, adjusting, and fiscal control. The latter expresses the main purpose of the tax - the formation of public funds of funds to finance the needs of the state and local communities.

  12. First-principle study on O–A–O dumbbell of delafossite crystal

    International Nuclear Information System (INIS)

    Jiang, H.F.; Gui, C.Y.; Zhu, Y.Y.; Wu, D.J.; Sun, S.P.; Xiong, C.; Zhu, X.B.

    2014-01-01

    Highlights: • From Cu to Ag, the increase of c parameters is attributed to electrostatic repulsion. • The difference charge density shows the bonding of Ag–O is more covalent. • Effective mass of AgAlO 2 along the [0 0 1] direction is smaller than that of CuAlO 2 . -- Abstract: Taking CuAlO 2 and AgAlO 2 for instance, O–A–O dumbbell-related electronic properties in delafossite lattice were systematically investigated by using the first-principles projector augmented wave method. Compared with CuAlO 2 , the increase of c parameter comes from the volume effect and electrostatic repulsion due to excess overlap of electron clouds between Ag and O atoms. The difference charge density demonstrates the interaction of A d z2 and O p z orbitals, and suggests the stronger covalent hybridization of Ag–O. The effective masses of these two compounds along [0 0 1] direction are remarkably different. Ag vacancy has lower formation energy relative to Cu one, which could benefit from longer c axis. The differences derived from O–A–O dumbbell could be helpful for thoroughly understanding its role in delafossite lattice

  13. Adsorption of CO molecules on doped graphene: A first-principles study

    Directory of Open Access Journals (Sweden)

    Weidong Wang

    2016-02-01

    Full Text Available As a typical kinds of toxic gases, CO plays an important role in environmental monitoring, control of chemical processes, space missions, agricultural and medical applications. Graphene is considered a potential candidate of gases sensor, so the adsorption of CO molecules on various graphene, including pristine graphene, Nitrogen-doped graphene (N-doped graphene and Aluminum-doped graphene (Al-doped graphene, are studied by using first-principles calculations. The optimal configurations, adsorption energies, charge transfer, and electronic properties including band structures, density of states and differential charge density are obtained. The adsorption energies of CO molecules on pristine graphene and N-doped graphene are −0.01 eV, and −0.03 eV, respectively. In comparison, the adsorption energy of CO on Al-doped graphene is much larger, −2.69 eV. Our results also show that there occurs a large amount of charge transfer between CO molecules and graphene sheet after the adsorption, which suggests Al-doped graphene is more sensitive to the adsorption of CO than pristine graphene and N-doped graphene. Therefore, the sensitivity of gases on graphene can be drastically improved by introducing the suitable dopants.

  14. First-principles study of γ-ray detector materials in perovskite halides

    Science.gov (United States)

    Im, Jino; Jin, Hosub; Stoumpos, Constantinos; Chung, Duck; Liu, Zhifu; Peters, John; Wessels, Bruce; Kanatzidis, Mercouri; Freeman, Arthur

    2013-03-01

    In an effort to search for good γ-ray detector materials, perovskite halide compounds containing heavy elements were investigated. Despite the three-dimensional network of the corner shared octahedra and the extended nature of the outermost shell, its strong ionic character leads to a large band gap, which is one of the essential criteria for γ-ray detector materials. Thus, considering high density and high atomic number, these pervoskite halides are possible candidate for γ-ray detector materials. We performed first-principles calculations to investigate electronic structures and thermodynamic properties of intrinsic defects in the selected perovskite halide, CsPbBr3. The screened-exchange local density approximation scheme was employed to correct the underestimation of the band gap in the LDA method. As a result, the calculated band gap of CsPbBr3 is found to be suitable for γ-ray detection. Furthermore, defect formation energy calculations allow us to predict thermodynamic and electronic properties of possible intrinsic defects, which affect detector efficiency and energy resolution. Supported by the office of Nonproliferation and Verification R &D under Contract No. DE-AC02-06CH11357

  15. Structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 phases from first-principles calculations

    Science.gov (United States)

    Li, X. D.; Li, K.; Wei, C. H.; Han, W. D.; Zhou, N. G.

    2018-06-01

    The structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 are systematically investigated by using first-principles calculations method based on density functional theory (DFT). The calculated formation enthalpies and cohesive energies show that CaSi2 possesses the greatest structural stability and CaSi has the strongest alloying ability. The structural stability of the three phases is compared according to electronic structures. Further analysis on electronic structures indicates that the bonding of these phases exhibits the combinations of metallic, covalent, and ionic bonds. The elastic constants are calculated, and the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factor of polycrystalline materials are deduced. Additionally, the thermodynamic properties were theoretically predicted and discussed.

  16. First-principles calculations on the four phases of BaTiO3.

    Science.gov (United States)

    Evarestov, Robert A; Bandura, Andrei V

    2012-04-30

    The calculations based on linear combination of atomic orbitals basis functions as implemented in CRYSTAL09 computer code have been performed for cubic, tetragonal, orthorhombic, and rhombohedral modifications of BaTiO(3) crystal. Structural and electronic properties as well as phonon frequencies were obtained using local density approximation, generalized gradient approximation, and hybrid exchange-correlation density functional theory (DFT) functionals for four stable phases of BaTiO(3). A comparison was made between the results of different DFT techniques. It is concluded that the hybrid PBE0 [J. P. Perdew, K. Burke, M. Ernzerhof, J. Chem. Phys. 1996, 105, 9982.] functional is able to predict correctly the structural stability and phonon properties both for cubic and ferroelectric phases of BaTiO(3). The comparative phonon symmetry analysis in BaTiO(3) four phases has been made basing on the site symmetry and irreducible representation indexes for the first time. Copyright © 2012 Wiley Periodicals, Inc.

  17. Effect of pressure on the Raman-active modes of zircon (ZrSiO4): a first-principles study

    Science.gov (United States)

    Sheremetyeva, Natalya; Cherniak, Daniele J.; Watson, E. Bruce; Meunier, Vincent

    2018-02-01

    Density-functional theory (DFT) was employed in a first-principles study of the effects of pressure on the Raman-active modes of zircon (ZrSiO4), using both the generalized gradient and local density approximations (GGA and LDA, respectively). Beginning with the equilibrium structure at zero pressure, we conducted a calibration of the effect of pressure in a manner procedurally similar to an experimental calibration. For pressures between 0 and 7 GPa, we find excellent qualitative agreement of frequency-pressure slopes partial ω /partial P calculated from GGA DFT with results of previous experimental studies. In addition, we were able to rationalize the ω vs. P behavior based on details of the vibrational modes and their atomic displacements. Most of the partial ω /partial P slopes are positive as expected, but the symmetry of the zircon lattice also results in two negative slopes for modes that involve slight shearing and rigid rotation of SiO4 tetrahedra. Overall, LDA yields absolute values of the frequencies of the Raman-active modes in good agreement with experimental values, while GGA reproduces the shift in frequency with pressure especially well.

  18. Rationalization of the Hubbard U parameter in CeOx from first principles: Unveiling the role of local structure in screening

    International Nuclear Information System (INIS)

    Lu, Deyu; Liu, Ping

    2014-01-01

    The density functional theory (DFT)+U method has been widely employed in theoretical studies on various ceria systems to correct the delocalization bias in local and semi-local DFT functionals with moderate computational cost. We present a systematic and quantitative study, aiming to gain better understanding of the dependence of Hubbard U on the local atomic arrangement. To rationalize the Hubbard U of Ce 4f, we employed the first principles linear response method to compute Hubbard U for Ce in ceria clusters, bulks, and surfaces. We found that the Hubbard U varies in a wide range from 4.3 eV to 6.7 eV, and exhibits a strong correlation with the Ce coordination number and Ce–O bond lengths, rather than the Ce 4f valence state. The variation of the Hubbard U can be explained by the changes in the strength of local screening due to O → Ce intersite transitions

  19. Hydrogenated and halogenated blue phosphorene as Dirac materials: A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Minglei [School of Mechanical Engineering, Southeast University, Nanjing, Jiangsu 211189 (China); Wang, Sake [Department of Physics, Southeast University, Nanjing, Jiangsu 210096 (China); Yu, Jin [School of Materials Science and Engineering, Southeast University, Nanjing, Jiangsu 211189 (China); Tang, Wencheng, E-mail: 101000185@seu.edu.cn [School of Mechanical Engineering, Southeast University, Nanjing, Jiangsu 211189 (China)

    2017-01-15

    Highlights: • The fully hydrogenated and halogenated blue phosphorenes are 2D Dirac materials. • The Dirac cone in fluorinated and iodinated blue phosphorenes lies exactly at the Fermi level. • The mass density of hydrogenated and fluorinated blue phosphorenes is rather small. - Abstract: Using first-principles calculations, we systematically investigate the structures and electronic properties of fully hydrogenated and halogenated blue phosphorene (P{sub 2}X{sub 2}). All these systems possess Dirac cone at high-symmetry K point, which are mainly contributed by P s p{sub x} p{sub y} orbitals. The Dirac cone in P{sub 2}F{sub 2} and P{sub 2}I{sub 2} systems lies exactly at the Fermi level. Formation energy analysis denotes that all the systems are energetically stable except P{sub 2}I{sub 2}. The mass density for P{sub 2}H{sub 2} and P{sub 2}F{sub 2} systems is rather small. Our calculations proposed that these systems, especially P{sub 2}F{sub 2} system, have great potential applications in future nanoelectronics.

  20. A first-principles study of phase transitions in ultrathin films of BaTiO 3

    Indian Academy of Sciences (India)

    We determine the effects of film thickness, epitaxial strain and the nature of electrodes on ferroelectric phase transitions in ultrathin films of BaTiO3 using a first-principles effective Hamiltonian in classical molecular dynamics simulations. We present results for polarization and dielectric properties as a function of temperature ...

  1. First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3

    International Nuclear Information System (INIS)

    Mubarak, A.A.; Al-Omari, Saleh

    2015-01-01

    We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF 3 and RbNiF 3 . The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior with indirect (M–Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra. - Highlights: • RbFeF 3 and RbNiCl 3 compounds are elastically stable. • RbFeF 3 and RbNiCl 3 compounds are classified as a ductile compound. • The RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior. • The optical properties were calculated for the radiation of up to 40 eV

  2. First-Principles Lattice Dynamics Method for Strongly Anharmonic Crystals

    Science.gov (United States)

    Tadano, Terumasa; Tsuneyuki, Shinji

    2018-04-01

    We review our recent development of a first-principles lattice dynamics method that can treat anharmonic effects nonperturbatively. The method is based on the self-consistent phonon theory, and temperature-dependent phonon frequencies can be calculated efficiently by incorporating recent numerical techniques to estimate anharmonic force constants. The validity of our approach is demonstrated through applications to cubic strontium titanate, where overall good agreement with experimental data is obtained for phonon frequencies and lattice thermal conductivity. We also show the feasibility of highly accurate calculations based on a hybrid exchange-correlation functional within the present framework. Our method provides a new way of studying lattice dynamics in severely anharmonic materials where the standard harmonic approximation and the perturbative approach break down.

  3. Electrical conductivity in oxygen-deficient phases of tantalum pentoxide from first-principles calculations

    International Nuclear Information System (INIS)

    Bondi, Robert J.; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J.

    2013-01-01

    We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta 2 O x (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V O n ; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V O 0 prefers equatorial O sites, while V O 1+ and V O 2+ are energetically preferred in the O cap sites of TaO 7 polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta 2 O x thin films (0.18 ≤ x ≤ 4.72) and bulk Ta 2 O 5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta 2 O 5 electronic structure provide further theoretical basis to substantiate V O 0 as a donor dopant in Ta 2 O 5 . Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V O n in Ta 2 O 5

  4. Intuitive Density Functional Theory-Based Energy Decomposition Analysis for Protein-Ligand Interactions.

    Science.gov (United States)

    Phipps, M J S; Fox, T; Tautermann, C S; Skylaris, C-K

    2017-04-11

    First-principles quantum mechanical calculations with methods such as density functional theory (DFT) allow the accurate calculation of interaction energies between molecules. These interaction energies can be dissected into chemically relevant components such as electrostatics, polarization, and charge transfer using energy decomposition analysis (EDA) approaches. Typically EDA has been used to study interactions between small molecules; however, it has great potential to be applied to large biomolecular assemblies such as protein-protein and protein-ligand interactions. We present an application of EDA calculations to the study of ligands that bind to the thrombin protein, using the ONETEP program for linear-scaling DFT calculations. Our approach goes beyond simply providing the components of the interaction energy; we are also able to provide visual representations of the changes in density that happen as a result of polarization and charge transfer, thus pinpointing the functional groups between the ligand and protein that participate in each kind of interaction. We also demonstrate with this approach that we can focus on studying parts (fragments) of ligands. The method is relatively insensitive to the protocol that is used to prepare the structures, and the results obtained are therefore robust. This is an application to a real protein drug target of a whole new capability where accurate DFT calculations can produce both energetic and visual descriptors of interactions. These descriptors can be used to provide insights for tailoring interactions, as needed for example in drug design.

  5. First principles-based adsorption comparison of group IV elements (C, Si, Ge, and Sn) on Au(111)/Ag(111) surface

    International Nuclear Information System (INIS)

    Chakraborty, Sudip; Rajesh, Ch.

    2012-01-01

    We have reported a first-principle investigation of the structural properties of monomer and dimer for group IV elements (C, Si, Ge, and Sn) adsorbed on the Au(111) and Ag(111) surfaces. The calculations were performed by means of a plane wave based pseudopotential method under the framework of density functional theory. The results reveal the preference of adatom to be adsorbed on the hexagonal closed packed site of the metal (111) surfaces with strong binding energy. The structures introduce interlayer forces in the adsorbate. The strong bonding with the surface atoms is a result of p–d hybridization. The adsorption energy follows a sequence as one goes down in the group IV elements which imply that the interaction of the group IV elements with Au/Ag is decreasing as the atomic number increases.

  6. First-principle calculations of structural, electronic, optical, elastic ...

    Indian Academy of Sciences (India)

    S CHEDDADI

    2017-11-28

    Nov 28, 2017 ... First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite ... The Kohn–Sham equations were solved using the ... RMTKmax = 7 was used for all the investigated systems,.

  7. Reason of method of density functional in classical and quantum statistical mechanisms

    International Nuclear Information System (INIS)

    Dinariev, O.Yu.

    2000-01-01

    Interaction between phenomenological description of a multi-component mixture on the basis of entropy functional with members, square in terms of component density gradients and temperature, on the one hand, and description in the framework of classical and quantum statistical mechanics, on the other hand, was investigated. Explicit expressions for the entropy functional in the classical and quantum theory were derived. Then a square approximation for the case of minor disturbances of uniform state was calculated. In the approximation the addends square in reference to the gradient were singlet out. It permits calculation of the relevant phenomenological coefficients from the leading principles [ru

  8. Phase stability, electronic, elastic and thermodynamic properties of Al-RE intermetallics in Mg-Al-RE alloy: A first principles study

    Directory of Open Access Journals (Sweden)

    H.L. Chen

    2015-09-01

    Full Text Available Electronic structure and elastic properties of Al2Y, Al3Y, Al2Gd and Al3Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory (DFT. The ground state energy and elastic constants of each phase were calculated, the formation enthalpy (ΔH, bulk modulus (B, shear modulus (G, Young's modulus (E, Poisson's ratio (ν and anisotropic coefficient (A were derived. The formation enthalpy shows that Al2RE is more stable than Al3RE, and Al-Y intermetallics have stronger phase stability than Al-Gd intermetallics. The calculated mechanical properties indicate that all these four intermetallics are strong and hard brittle phases, it may lead to the similar performance when deforming due to their similar elastic constants. The total and partial electron density of states (DOS, Mulliken population and metallicity were calculated to analyze the electron structure and bonding characteristics of the phases. Finally, phonon calculation was conducted, and the thermodynamic properties were obtained and further discussed.

  9. First-principles study of structural, electronic, linear and nonlinear optical properties of Ga{2}PSb ternary chalcopyrite

    Science.gov (United States)

    Ouahrani, T.; Reshak, A. H.; de La Roza, A. Otero; Mebrouki, M.; Luaña, V.; Khenata, R.; Amrani, B.

    2009-12-01

    We report results from first-principles density functional calculations using the full-potential linear augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) and the Engel-Vosko-generalized gradient approximation (EV-GGA) were used for the exchange-correlation energy of the structural, electronic, linear and nonlinear optical properties of the chalcopyrite Ga2PSb compound. The valence band maximum (VBM) is located at the Γv point, and the conduction band minimum (CBM) is located at the Γc point, resulting in a direct band gap of about 0.365 eV for GGA and 0.83 eV for EV-GGA. In comparison with the experimental one (1.2 eV) we found that EV-GGA calculation gives energy gap in reasonable agreement with the experiment. The spin orbit coupling has marginal influence on the optical properties. The ground state quantities such as lattice parameters (a, c and u), bulk modules B and its pressure derivative B^primeare evaluated.

  10. A methodology to aid in the design of naval steels: Linking first principles calculations to mesoscale modeling

    International Nuclear Information System (INIS)

    Spanos, G.; Geltmacher, A.B.; Lewis, A.C.; Bingert, J.F.; Mehl, M.; Papaconstantopoulos, D.; Mishin, Y.; Gupta, A.; Matic, P.

    2007-01-01

    This paper provides a brief overview of a multidisciplinary effort at the Naval Research Laboratory aimed at developing a computationally-based methodology to assist in the design of advanced Naval steels. This program uses multiple computational techniques ranging from the atomistic length scale to continuum response. First-principles electronic structure calculations using density functional theory were employed, semi-empirical angular dependent potentials were developed based on the embedded atom method, and these potentials were used as input into Monte-Carlo and molecular dynamics simulations. Experimental techniques have also been applied to a super-austenitic stainless steel (AL6XN) to provide experimental input, guidance, verification, and enhancements to the models. These experimental methods include optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and serial sectioning in conjunction with computer-based three-dimensional reconstruction and quantitative analyses. The experimental results are also used as critical input into mesoscale finite element models of materials response

  11. First-principles investigation of diffusion and defect properties of Fe and Ni in Cr2O3

    Science.gov (United States)

    Rak, Zs.; Brenner, D. W.

    2018-04-01

    Diffusion of Fe and Ni and the energetics of Fe- and Ni-related defects in chromium oxide (α-Cr2O3) are investigated using first-principles Density Functional Theory calculations in combination with the climbing-image nudged elastic band method. The orientations of the spin magnetic moments of the migrating ions are taken into account and their effects on migration barriers are examined. Several possible diffusion pathways were explored through interstitial and vacancy mechanisms, and it was found that the principal mode of ion transport in Cr2O3 is via vacancies. Both interstitial- and vacancy-mediated diffusions are anisotropic, with diffusion being faster in the z-direction. The energetics of defect formation indicates that the Ni-related defects are less stable than the Fe-related ones. This is consistent with Ni-diffusion being faster than Fe-diffusion. The results are compared with previous theoretical and experimental data and possible implications in corrosion control are discussed.

  12. Insight into point defects and impurities in titanium from first principles

    Science.gov (United States)

    Nayak, Sanjeev K.; Hung, Cain J.; Sharma, Vinit; Alpay, S. Pamir; Dongare, Avinash M.; Brindley, William J.; Hebert, Rainer J.

    2018-03-01

    Titanium alloys find extensive use in the aerospace and biomedical industries due to a unique combination of strength, density, and corrosion resistance. Decades of mostly experimental research has led to a large body of knowledge of the processing-microstructure-properties linkages. But much of the existing understanding of point defects that play a significant role in the mechanical properties of titanium is based on semi-empirical rules. In this work, we present the results of a detailed self-consistent first-principles study that was developed to determine formation energies of intrinsic point defects including vacancies, self-interstitials, and extrinsic point defects, such as, interstitial and substitutional impurities/dopants. We find that most elements, regardless of size, prefer substitutional positions, but highly electronegative elements, such as C, N, O, F, S, and Cl, some of which are common impurities in Ti, occupy interstitial positions.

  13. High pressure stability analysis and chemical bonding of Ti1-xZrxN alloy: A first principle study

    International Nuclear Information System (INIS)

    Chauhan, Mamta; Gupta, Dinesh C.

    2016-01-01

    First-principles pseudo-potential calculations have been performed to analyze the stability of Ti 1-x Zr x N alloy under high pressures. The first order phase transition from B1 to B2 phase has been observed in this alloy at high pressure. The variation of lattice parameter with the change in concentration of Zr atom in Ti 1-x Zr x N is also reported in both the phases. The calculations for density of states have been performed to understand the alloying effects on chemical bonding of Ti-Zr-N alloy.

  14. Mechanical properties and chemical bonding of the Os–B system: A first-principles study

    International Nuclear Information System (INIS)

    Ji Zongwei; Hu Chaohao; Wang Dianhui; Zhong Yan; Yang Jiong; Zhang Wenqing; Zhou Huaiying

    2012-01-01

    The mechanical properties of Os–B compounds containing different boron contents have been investigated systemically by first-principles calculations. Two previously unreported crystal structures of Os 2 B 5 and OsB 3 , crystallizing in space groups R3m and P-6m2 respectively, are determined using the ab initio evolutionary structure prediction. The calculated elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and hardness for Os–B compounds are in good agreement with the available experimental values. Our results show that the hardness of osmium borides increases with increasing boron content. Os 2 B 5 and OsB 3 , with hardnesses of 34.4 and 36.9 GPa respectively, can almost be considered as potential superhard materials. Further analyses on density of states, crystal orbital Hamilton population, and electron localization function demonstrate that the electronic structure of Os–B compounds is directly responsible for their particular mechanical properties. High hardness in Os 2 B 5 and OsB 3 is mainly attributed to the occurrence of strong B–B covalent bonds and the disappearance of some ductile Os–Os metallic bonds.

  15. First-principles study on ferrite/TiC heterogeneous nucleation interface

    International Nuclear Information System (INIS)

    Yang, Jian; Zhang, Pengfei; Zhou, Yefei; Guo, Jing; Ren, Xuejun; Yang, Yulin; Yang, Qingxiang

    2013-01-01

    Highlights: ► Interface stability of ferrite (1 0 0)/TiC (1 0 0) was studied. ► The effectiveness of TiC as the heterogeneous nuclei of ferrite was analyzed. ► Ti-termination and C-termination are the two binding modes for ferrite/TiC interface. ► Interfacial energy of the Ti-termination is larger than that of the C-termination. ► On C-termination, ability of TiC promotes ferrite heterogeneous nucleation is strong. -- Abstract: Interface atomic structure, bonding character, cohesive energy and interfacial energy of ferrite (1 0 0)/TiC (1 0 0) were studied using a first-principles density functional plane-wave ultrasoft pseudopotential method. Meanwhile, the effectiveness of TiC as the heterogeneous nuclei of ferrite was analyzed. The results indicated that, TiC bonding is dominated by the C-2p, C-2s and Ti-3d electrons, which exhibits high covalency. With increase of the atomic layers, the interfacial energies of ferrite and TiC are both declined rapidly and stabilized gradually. There are two binding modes for TiC as the heterogeneous nuclei of ferrite, which are Fe atoms above the Ti atoms (Ti-termination) and Fe atoms above the C atoms (C-termination). Interfacial energy of the Ti-termination is larger than that of the C-termination, which means that for Fe atoms above the C atoms, the ability of TiC promotes ferrite heterogeneous nucleation on its surface is larger than that for Fe atoms above the Ti atoms

  16. First-principles study of crystal structure, elastic stiffness constants, piezoelectric constants, and spontaneous polarization of orthorhombic Pna21-M2O3 (M = Al, Ga, In, Sc, Y)

    Science.gov (United States)

    Shimada, Kazuhiro

    2018-03-01

    We perform first-principles calculations to investigate the crystal structure, elastic and piezoelectric properties, and spontaneous polarization of orthorhombic M2O3 (M = Al, Ga, In, Sc, Y) with Pna21 space group based on density functional theory. The lattice parameters, full elastic stiffness constants, piezoelectric stress and strain constants, and spontaneous polarization are successfully predicted. Comparison with available experimental and computational results indicates the validity of our computational results. Detailed analysis of the results clarifies the difference in the bonding character and the origin of the strong piezoelectric response and large spontaneous polarization.

  17. Electronic Structure and Transport in Solids from First Principles

    Science.gov (United States)

    Mustafa, Jamal Ibrahim

    The focus of this dissertation is the determination of the electronic structure and trans- port properties of solids. We first review some of the theory and computational methodology used in the calculation of electronic structure and materials properties. Throughout the dissertation, we make extensive use of state-of-the-art software packages that implement density functional theory, density functional perturbation theory, and the GW approximation, in addition to specialized methods for interpolating matrix elements for extremely accurate results. The first application of the computational framework introduced is the determination of band offsets in semiconductor heterojunctions using a theory of quantum dipoles at the interface. This method is applied to the case of heterojunction formed between a new metastable phase of silicon, with a rhombohedral structure, and cubic silicon. Next, we introduce a novel method for the construction of localized Wannier functions, which we have named the optimized projection functions method (OPFM). We illustrate the method on a variety of systems and find that it can reliably construct localized Wannier functions with minimal user intervention. We further develop the OPFM to investigate a class of materials called topological insulators, which are insulating in the bulk but have conductive surface states. These properties are a result of a nontrivial topology in their band structure, which has interesting effects on the character of the Wannier functions. In the last sections of the main text, the noble metals are studied in great detail, including their electronic properties and carrier dynamics. In particular, we investigate, the Fermi surface properties of the noble metals, specifically electron-phonon scattering lifetimes, and subsequently the transport properties determined by carriers on the Fermi surface. To achieve this, a novel sampling technique is developed, with wide applicability to transport calculations

  18. First-principles study of lattice dynamics, structural phase transition, and thermodynamic properties of barium titanate

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Huai-Yong; Zhao, Ying-Qin; Lu, Qing [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Zeng, Zhao-Yi [Chongqing Normal Univ. (China). College of Physics and Electronic Engineering; Chinese Academy of Engineering Physics, Mianyang (China). National Key Laboratory for Shock Wave and Detonation Physics Research; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Sichuan Univ., Chengdu (China). Key Laboratory of High Energy Density Physics and Technology of Ministry of Education

    2016-11-01

    Lattice dynamics, structural phase transition, and the thermodynamic properties of barium titanate (BaTiO{sub 3}) are investigated by using first-principles calculations within the density functional theory (DFT). It is found that the GGA-WC exchange-correlation functional can produce better results. The imaginary frequencies that indicate structural instability are observed for the cubic, tetragonal, and orthorhombic phases of BaTiO{sub 3} and no imaginary frequencies emerge in the rhombohedral phase. By examining the partial phonon density of states (PDOSs), we find that the main contribution to the imaginary frequencies is the distortions of the perovskite cage (Ti-O). On the basis of the site-symmetry consideration and group theory, we give the comparative phonon symmetry analysis in four phases, which is useful to analyze the role of different atomic displacements in the vibrational modes of different symmetry. The calculated optical phonon frequencies at Γ point for the four phases are in good agreement with other theoretical and experimental data. The pressure-induced phase transition of BaTiO{sub 3} among four phases and the thermodynamic properties of BaTiO{sub 3} in rhombohedral phase have been investigated within the quasi-harmonic approximation (QHA). The sequence of the pressure-induced phase transition is rhombohedral → orthorhombic → tetragonal → cubic, and the corresponding transition pressure is 5.17, 5.92, 6.65 GPa, respectively. At zero pressure, the thermal expansion coefficient α{sub V}, heat capacity C{sub V}, Grueneisen parameter γ, and bulk modulus B of the rhombohedral phase BaTiO{sub 3} are estimated from 0 K to 200 K.

  19. First-principles calculations of a half-metallic ferromagnet zinc blende Zn{sub 1−x}V{sub x}Te

    Energy Technology Data Exchange (ETDEWEB)

    El Amine Monir, M.; Baltache, H. [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Azam, Sikander [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University Setif 1, 19000 Setif (Algeria); Al-Douri, Y. [Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Ali, Roshan [Materials Modeling Lab, Department of Physics, Post Graduate Jahanzeb College, Swat (Pakistan)

    2015-03-15

    First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn{sub 1−x}V{sub x}Te for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn{sub 1−x}V{sub x}Te alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C{sub 11}, C{sub 12} and C{sub 44} are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn{sub 0.50}V{sub 0.50}Te and Zn{sub 0.75}V{sub 0.25}Te exhibit a half-metallic character, while Zn{sub 0.25}V{sub 0.75}Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δ{sub x}(d) and Δ{sub x}(pd) produced by the V(3d)-doped and s(p)–d exchange constants N{sub 0α} (conduction band) and N{sub 0β} (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µ{sub B} and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model. - Highlights: • Some physical properties of Vanadium doped ZnTe have been investigated. • Structural parameters for the parent compounds compare well with the available data. • The elastic and thermal properties are studied for the first time.

  20. Cesium under pressure: First-principles calculation of the bcc-to-fcc phase transition

    Science.gov (United States)

    Carlesi, S.; Franchini, A.; Bortolani, V.; Martinelli, S.

    1999-05-01

    In this paper we present the ab initio calculation of the structural properties of cesium under pressure. The calculation of the total energy is done in the local-density approximation of density-functional theory, using a nonlocal pseudopotential including the nonlinear core corrections proposed by Louie et al. The calculation of the pressure-volume diagram for both bcc and fcc structures allows us to prove that the transition from bcc to fcc structure is a first-order transition.

  1. Intra- and inter-atomic optical transitions of Fe, Co, and Ni ferrocyanides studied using first-principles many-electron calculations

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, Shinta, E-mail: s-watanabe@nucl.nagoya-u.ac.jp, E-mail: j-onoe@nucl.nagoya-u.ac.jp; Sawada, Yuki; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Onoe, Jun, E-mail: s-watanabe@nucl.nagoya-u.ac.jp, E-mail: j-onoe@nucl.nagoya-u.ac.jp [Department of Materials, Physics and Energy Engineering, Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Kameyama, Tatsuya; Torimoto, Tsukasa [Department of Crystalline Materials Science, Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Inaba, Yusuke; Takahashi, Hideharu; Takeshita, Kenji [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-16 O-okayama, Meguro-ku, Tokyo 152-8550 (Japan)

    2016-06-21

    We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe{sup 2+} to Fe{sup 3+} but also the 3d-3d intra-transitions of Fe{sup 3+} ions. In addition, the spin crossover transition of Fe{sup 3+} predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe{sup 2+} ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption peaks originated from the 3d-3d intra-transitions of Ni{sup 3+} ions in a low-energy region, while from both the 3d-3d intra-transitions of Fe{sup 2+} ions and the charge-transfer transitions from Fe{sup 2+} to Ni{sup 3+} in a high-energy region. These results were quite different from those of density-functional theory (DFT) calculations. The discrepancy between the results of DFT calculations and those of many-electron calculations suggested that the intra- and inter-atomic transitions of transition metal ions are significantly affected by the many-body effects of strongly correlated 3d electrons.

  2. Underscreening in ionic liquids: a first principles analysis

    Science.gov (United States)

    Rotenberg, Benjamin; Bernard, Olivier; Hansen, Jean-Pierre

    2018-02-01

    An attempt is made to understand the underscreening effect, observed in concentrated electrolyte solutions or melts, on the basis of simple, admittedly crude models involving charged (for the ions) and neutral (for the solvent molecules) hard spheres. The thermodynamic and structural properties of these ‘primitive’ and ‘semi-primitive’ models are calculated within mean spherical approximation, which provides the basic input required to determine the partial density response functions. The screening length λS , which is unambiguously defined in terms of the wave-number-dependent response functions, exhibits a cross-over from a low density, Debye-like regime, to a regime where λS increases with density beyond a critical density at which the Debye length λD becomes comparable to the ion diameter. In this high density regime the ratio λ_S/λD increases according to a power law, in qualitative agreement with experimental measurements, albeit at a much slower rate.

  3. Borophene as an anode material for Ca, Mg, Na or Li ion storage: A first-principle study

    Science.gov (United States)

    Mortazavi, Bohayra; Dianat, Arezoo; Rahaman, Obaidur; Cuniberti, Gianaurelio; Rabczuk, Timon

    2016-10-01

    Borophene, the boron atom analogue to graphene, being atomic thick have been just recently experimentally fabricated. In this work, we employ first-principles density functional theory calculations to investigate the interaction of Ca, Mg, Na or Li atoms with single-layer and free-standing borophene. We first identified the most stable binding sites and their corresponding binding energies as well and then we gradually increased the ions concentration. Our calculations predict strong binding energies of around 4.03 eV, 2.09 eV, 2.92 eV and 3.28 eV between the borophene substrate and Ca, Mg, Na or Li ions, respectively. We found that the binding energy generally decreases by increasing the ions content. Using the Bader charge analysis, we evaluate the charge transfer between the adatoms and the borophene sheet. Our investigation proposes the borophene as a 2D material with a remarkably high capacity of around 800 mA h/g, 1960 mA h/g, 1380 mA h/g and 1720 mA h/g for Ca, Mg, Na or Li ions storage, respectively. This study can be useful for the possible application of borophene for the rechargeable ion batteries.

  4. First principle calculations of effective exchange integrals: Comparison between SR (BS) and MR computational results

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, Kizashi [Institute for Nano Science Design Center, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan and TOYOTA Physical and Chemical Research Institute, Nagakute, Aichi, 480-1192 (Japan); Nishihara, Satomichi; Saito, Toru; Yamanaka, Shusuke; Kitagawa, Yasutaka; Kawakami, Takashi; Yamada, Satoru; Isobe, Hiroshi; Okumura, Mitsutaka [Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)

    2015-01-22

    First principle calculations of effective exchange integrals (J) in the Heisenberg model for diradical species were performed by both symmetry-adapted (SA) multi-reference (MR) and broken-symmetry (BS) single reference (SR) methods. Mukherjee-type (Mk) state specific (SS) MR coupled-cluster (CC) calculations by the use of natural orbital (NO) references of ROHF, UHF, UDFT and CASSCF solutions were carried out to elucidate J values for di- and poly-radical species. Spin-unrestricted Hartree Fock (UHF) based coupled-cluster (CC) computations were also performed to these species. Comparison between UHF-NO(UNO)-MkMRCC and BS UHF-CC computational results indicated that spin-contamination of UHF-CC solutions still remains at the SD level. In order to eliminate the spin contamination, approximate spin-projection (AP) scheme was applied for UCC, and the AP procedure indeed corrected the error to yield good agreement with MkMRCC in energy. The CC double with spin-unrestricted Brueckner's orbital (UBD) was furthermore employed for these species, showing that spin-contamination involved in UHF solutions is largely suppressed, and therefore AP scheme for UBCCD removed easily the rest of spin-contamination. We also performed spin-unrestricted pure- and hybrid-density functional theory (UDFT) calculations of diradical and polyradical species. Three different computational schemes for total spin angular momentums were examined for the AP correction of the hybrid (H) UDFT. HUDFT calculations followed by AP, HUDFT(AP), yielded the S-T gaps that were qualitatively in good agreement with those of MkMRCCSD, UHF-CC(AP) and UB-CC(AP). Thus a systematic comparison among MkMRCCSD, UCC(AP) UBD(AP) and UDFT(AP) was performed concerning with the first principle calculations of J values in di- and poly-radical species. It was found that BS (AP) methods reproduce MkMRCCSD results, indicating their applicability to large exchange coupled systems.

  5. Structural, elastic, mechanical and thermodynamic properties of Terbium oxide: First-principles investigations

    Directory of Open Access Journals (Sweden)

    Samah Al-Qaisi

    Full Text Available First-principles investigations of the Terbium oxide TbO are performed on structural, elastic, mechanical and thermodynamic properties. The investigations are accomplished by employing full potential augmented plane wave FP-LAPW method framed within density functional theory DFT as implemented in the WIEN2k package. The exchange-correlation energy functional, a part of the total energy functional, is treated through Perdew Burke Ernzerhof scheme of the Generalized Gradient Approximation PBEGGA. The calculations of the ground state structural parameters, like lattice constants a0, bulk moduli B and their pressure derivative B′ values, are done for the rock-salt RS, zinc-blende ZB, cesium chloride CsCl, wurtzite WZ and nickel arsenide NiAs polymorphs of the TbO compound. The elastic constants (C11, C12, C13, C33, and C44 and mechanical properties (Young’s modulus Y, Shear modulus S, Poisson’s ratio σ, Anisotropic ratio A and compressibility β, were also calculated to comprehend its potential for valuable applications. From our calculations, the RS phase of TbO compound was found strongest one mechanically amongst the studied cubic structures whereas from hexagonal phases, the NiAs type structure was found stronger than WZ phase of the TbO. To analyze the ductility of the different structures of the TbO, Pugh’s rule (B/SH and Cauchy pressure (C12–C44 approaches are used. It was found that ZB, CsCl and WZ type structures of the TbO were of ductile nature with the obvious dominance of the ionic bonding while RS and NiAs structures exhibited brittle nature with the covalent bonding dominance. Moreover, Debye temperature was calculated for both cubic and hexagonal structures of TbO in question by averaging the computed sound velocities. Keywords: DFT, TbO, Elastic properties, Thermodynamic properties

  6. Thermodynamic assessment of the Sn–Sr system supported by first-principles calculations

    International Nuclear Information System (INIS)

    Zhao, Jingrui; Du, Yong; Zhang, Lijun; Wang, Aijun; Zhou, Liangcai; Zhao, Dongdong; Liang, Jianlie

    2012-01-01

    Highlights: ► All the literature data of Sn–Sr system is critically reviewed. ► First-principles calculation of enthalpy of formation is carried out for each compound. ► Thermodynamic parameters for Sn–Sr system are obtained by CALPHAD method. ► A hybrid approach of CALPHAD and first-principles calculations is recommended. - Abstract: A hybrid approach of CALPHAD and first-principles calculations was employed to perform a thermodynamic modeling of the Sn–Sr system. The experimental phase diagram and thermodynamic data available in the literature were critically reviewed. The enthalpies of formation for the 6 stoichiometric compounds (i.e. Sr 2 Sn, Sr 5 Sn 3 , SrSn, Sr 3 Sn 5 , SrSn 3 and SrSn 4 ) at 0 K were computed by means of first-principles calculations. These data were used as the experimental values in the optimization module PARROT in the subsequent CALPHAD assessment to provide thermodynamic parameters with sound physical meaning. A set of self-consistent thermodynamic parameters was finally obtained by considering reliable literature data and the first-principles computed results. Comprehensive comparisons between the calculated and measured quantities indicate that all the reliable experimental information can be satisfactorily accounted for by the present thermodynamic description.

  7. First-principles thermodynamics and defect kinetics guidelines for engineering a tailored RRAM device

    International Nuclear Information System (INIS)

    Clima, Sergiu; Chen, Yang Yin; Goux, Ludovic; Govoreanu, Bogdan; Degraeve, Robin; Fantini, Andrea; Jurczak, Malgorzata; Chen, Chao Yang; Pourtois, Geoffrey

    2016-01-01

    Resistive Random Access Memories are among the most promising candidates for the next generation of non-volatile memory. Transition metal oxides such as HfOx and TaOx attracted a lot of attention due to their CMOS compatibility. Furthermore, these materials do not require the inclusion of extrinsic conducting defects since their operation is based on intrinsic ones (oxygen vacancies). Using Density Functional Theory, we evaluated the thermodynamics of the defects formation and the kinetics of diffusion of the conducting species active in transition metal oxide RRAM materials. The gained insights based on the thermodynamics in the Top Electrode, Insulating Matrix and Bottom Electrode and at the interfaces are used to design a proper defect reservoir, which is needed for a low-energy reliable switching device. The defect reservoir has also a direct impact on the retention of the Low Resistance State due to the resulting thermodynamic driving forces. The kinetics of the diffusing conducting defects in the Insulating Matrix determine the switching dynamics and resistance retention. The interface at the Bottom Electrode has a significant impact on the low-current operation and long endurance of the memory cell. Our first-principles findings are confirmed by experimental measurements on fabricated RRAM devices.

  8. First-principles thermodynamics and defect kinetics guidelines for engineering a tailored RRAM device

    Energy Technology Data Exchange (ETDEWEB)

    Clima, Sergiu, E-mail: clima@imec.be; Chen, Yang Yin; Goux, Ludovic; Govoreanu, Bogdan; Degraeve, Robin; Fantini, Andrea; Jurczak, Malgorzata [imec, Kapeldreef 75, 3001 Leuven (Belgium); Chen, Chao Yang [imec, Kapeldreef 75, 3001 Leuven (Belgium); Katholieke Universiteit Leuven, 3001 Leuven (Belgium); Pourtois, Geoffrey [imec, Kapeldreef 75, 3001 Leuven (Belgium); PLASMANT, University of Antwerp, 2610 Antwerpen (Belgium)

    2016-06-14

    Resistive Random Access Memories are among the most promising candidates for the next generation of non-volatile memory. Transition metal oxides such as HfOx and TaOx attracted a lot of attention due to their CMOS compatibility. Furthermore, these materials do not require the inclusion of extrinsic conducting defects since their operation is based on intrinsic ones (oxygen vacancies). Using Density Functional Theory, we evaluated the thermodynamics of the defects formation and the kinetics of diffusion of the conducting species active in transition metal oxide RRAM materials. The gained insights based on the thermodynamics in the Top Electrode, Insulating Matrix and Bottom Electrode and at the interfaces are used to design a proper defect reservoir, which is needed for a low-energy reliable switching device. The defect reservoir has also a direct impact on the retention of the Low Resistance State due to the resulting thermodynamic driving forces. The kinetics of the diffusing conducting defects in the Insulating Matrix determine the switching dynamics and resistance retention. The interface at the Bottom Electrode has a significant impact on the low-current operation and long endurance of the memory cell. Our first-principles findings are confirmed by experimental measurements on fabricated RRAM devices.

  9. Boron, nitrogen, and nickel impurities in GeC nanoribbons: A first-principles investigation

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Zhuo; Li, Yangping, E-mail: liyp@nwpu.edu.cn; Liu, Zhengtang

    2017-07-01

    Highlights: • The impurities preferentially substitutes the Ge atom at the ribbon edge. • The impurities could result in a reduction of the band gap of 7-AGeCNR. • The impurities turns the metallic behavior of 4-ZGeCNR into semiconductor. • The impurities could change the magnetic moment of 4-ZGeCNR. • The impurities could introduce magnetic moments into the non-magnetic 7-AGeCNR. - Abstract: Using first-principles calculations based on the density functional theory we investigated the structural, electronic and magnetic properties of substitutional boron, nitrogen, and nickel impurities in germanium carbide (GeC) nanoribbons. Hydrogen terminated GeC ribbons with armchair and zigzag edges are considered here. We observed that all three impurities preferentially substitutes the Ge atom at the ribbon edge. In addition, the electronic band structures of the doped systems indicate that (i) the impurities could introduce impurity bands in the band gap and resulting in a reduction of the band gap of 7-AGeCNR, (ii) the metallic behavior of 4-ZGeCNR turns into semiconductor because of the incorporation of the impurities, (iii) the impurities could change the magnetic moment of 4-ZGeCNR and even introduce magnetic moment into the non-magnetic 7-AGeCNR.

  10. Anchoring platinum on graphene using metallic adatoms: a first principles investigation

    International Nuclear Information System (INIS)

    Sen, F G; Alpas, A T; Qi, Y

    2012-01-01

    First principles calculations based on spin-polarized density functional theory were used to identify metallic adatoms that would strengthen the Pt(111)/graphene interface (with a low work of separation of 0.009 J m -2 ), when the adatom was placed between the Pt(111) and the graphene. It was shown that the strength of the Pt-adatom bond, which had a metallic character, increased with the amount of charge transferred from the adatom to the Pt. The carbon-adatom bond, on the other hand, had a mixed ionic and covalent character and was weaker than the Pt-adatom bond for each of the 25 elements considered. Consequently, the total Pt(111)/graphene interface strength and, hence, the anchoring effect of the adatom were controlled by the carbon-adatom bond strength. Metals with unfilled d orbitals increased the Pt/graphene interface strength to above 0.5 J m -2 . The carbon-adatom bond strength was proportional to the ratio between the charge transferred from the adatom to the graphene (ΔZ C ) and the charge transferred to the Pt surface (ΔZ Pt ); i.e., the ΔZ C /ΔZ Pt ratio defined the ability of an adatom to anchor Pt to graphene. For Ir, Os, Ru, Rh and Re, ΔZ C /ΔZ Pt > 1.0, making these elements the most effective adatoms for anchoring Pt to graphene. (paper)

  11. Density-density functionals and effective potentials in many-body electronic structure calculations

    International Nuclear Information System (INIS)

    Reboredo, Fernando A.; Kent, Paul R.

    2008-01-01

    We demonstrate the existence of different density-density functionals designed to retain selected properties of the many-body ground state in a non-interacting solution starting from the standard density functional theory ground state. We focus on diffusion quantum Monte Carlo applications that require trial wave functions with optimal Fermion nodes. The theory is extensible and can be used to understand current practices in several electronic structure methods within a generalized density functional framework. The theory justifies and stimulates the search of optimal empirical density functionals and effective potentials for accurate calculations of the properties of real materials, but also cautions on the limits of their applicability. The concepts are tested and validated with a near-analytic model.

  12. Semi-local machine-learned kinetic energy density functional with third-order gradients of electron density

    Science.gov (United States)

    Seino, Junji; Kageyama, Ryo; Fujinami, Mikito; Ikabata, Yasuhiro; Nakai, Hiromi

    2018-06-01

    A semi-local kinetic energy density functional (KEDF) was constructed based on machine learning (ML). The present scheme adopts electron densities and their gradients up to third-order as the explanatory variables for ML and the Kohn-Sham (KS) kinetic energy density as the response variable in atoms and molecules. Numerical assessments of the present scheme were performed in atomic and molecular systems, including first- and second-period elements. The results of 37 conventional KEDFs with explicit formulae were also compared with those of the ML KEDF with an implicit formula. The inclusion of the higher order gradients reduces the deviation of the total kinetic energies from the KS calculations in a stepwise manner. Furthermore, our scheme with the third-order gradient resulted in the closest kinetic energies to the KS calculations out of the presented functionals.

  13. Non-local energy density functionals: models plus some exact general results

    International Nuclear Information System (INIS)

    March, N.H.

    2001-02-01

    Holas and March (Phys. Rev. A51, 2040, 1995) gave a formally exact expression for the force - δV xc (r-tilde)/δr-tilde associated with the exchange-correlation potential V xc (r-tilde) of density functional theory. This forged a precise link between first- and second-order density matrices and V xc (r-tilde). Here models are presented in which these low-order matrices can be related to the ground-state electron density. This allows non-local energy density functionals to be constructed within the framework of such models. Finally, results emerging from these models have led to the derivation of some exact 'nuclear cusp' relations for exchange and correlation energy densities in molecules, clusters and condensed phases. (author)

  14. Robust design principles for reducing variation in functional performance

    DEFF Research Database (Denmark)

    Christensen, Martin Ebro; Howard, Thomas J.

    2016-01-01

    This paper identifies, describes and classifies a comprehensive collection of variation reduction principles (VRP) that can be used to increase the robustness of a product and reduce its variation in functional performance. Performance variation has a negative effect on the reliability and percei......This paper identifies, describes and classifies a comprehensive collection of variation reduction principles (VRP) that can be used to increase the robustness of a product and reduce its variation in functional performance. Performance variation has a negative effect on the reliability...... and perceived quality of a product and efforts should be made to minimise it. The design principles are identified by a systematic decomposition of the Taguchi Transfer Function in combination with the use of existing literature and the authors’ experience. The paper presents 15 principles and describes...... their advantages and disadvantages along with example cases. Subsequently, the principles are classified based on their applicability in the various development and production stages. The VRP are to be added to existing robust design methodologies, helping the designer to think beyond robust design tool and method...

  15. A first-principles study on adsorption behaviors of pristine and Li-decorated graphene sheets toward hydrazine molecules

    Science.gov (United States)

    Zeng, Huadong; Cheng, Xinlu; Wang, Wei

    2018-03-01

    The adsorption behaviors and properties of hydrazine (N2H4) molecules on pristine and Li-decorated graphene sheets were investigated by means of first-principles based on density functional theory. We systematically analyzed the optimal geometry, average binding energy, charge transfer, charge density difference and density of states of N2H4 molecules adsorbed on pristine and Li-decorated graphene sheets. It is found that the interaction between single N2H4 molecule and pristine graphene is weak physisorption with the low binding energy of -0.026 eV, suggesting that the pristine graphene sheet is insensitive to the presence of N2H4 molecule. However, it is markedly enhanced after lithium decoration with the high binding energy of -1.004 eV, verifying that the Li-decorated graphene sheet is significantly sensitive to detect N2H4 molecule. Meanwhile, the effects of the concentrations of N2H4 molecules on two different substrates were studied detailedly. For pristine graphene substrate, the average binding energy augments apparently with increasing the number of N2H4 molecules, which is mainly attributed to the van der Waals interactions and hydrogen bonds among N2H4 clusters. Li-decorated graphene sheet has still a strong affinity to N2H4 molecules despite the corresponding average binding energy emerges a contrary tendency. Overall, Li-decorated graphene sheet could be considered as a potential gas sensor in field of hydrazine molecules.

  16. Density Functional Theory Study of Leaching Performance of Different Acids on Pyrochlore (100) Surface

    Science.gov (United States)

    Yang, Xiuli; Fang, Qing; Ouyang, Hui

    2018-06-01

    Pyrochlore leaching using hydrofluoric, sulfuric, and hydrochloric acids has been studied via experimental methods for years, but the interactions between niobium atoms on the pyrochlore surface and different acids have not been investigated. In this work, first-principles calculations based on density functional theory were used to elucidate the leaching performance of these three acids from the viewpoint of geometrical and electronic structures. The calculation results indicate that sulfate, chloride, and fluoride anions influence the geometric structure of pyrochlore (100) to different extents, decreasing in the order: sulfate, fluoride, chloride. Orbitals of O1 and O2 atoms of sulfate hybridized with those of surface niobium atom. Fluorine orbitals hybridized with those of surface niobium atoms. However, no obvious overlap exists between any orbitals of chlorine and surface niobium, revealing that chlorine does not interact chemically with surface niobium atoms.

  17. First-principles study of point-defect production in Si and SiC

    International Nuclear Information System (INIS)

    Windl, W.; Lenosky, T.J.; Kress, J.D.; Voter, A.F.

    1998-03-01

    The authors have calculated the displacement-threshold energy E(d) for point-defect production in Si and SiC using empirical potentials, tight-binding, and first-principles methods. They show that -- depending on the knock-on direction -- 64-atom simulation cells can be sufficient to allow a nearly finite-size-effect-free calculation, thus making the use of first-principles methods possible. They use molecular dynamics (MD) techniques and propose the use of a sudden approximation which agrees reasonably well with the MD results for selected directions and which allows estimates of Ed without employing an MD simulation and the use of computationally demanding first-principles methods. Comparing the results with experiment, the authors find the full self-consistent first-principles method in conjunction with the sudden approximation to be a reliable and easy method to predict E d . Furthermore, they have examined the temperature dependence of E d for C in SiC and found it to be negligible

  18. Excited-state density functional theory

    International Nuclear Information System (INIS)

    Harbola, Manoj K; Hemanadhan, M; Shamim, Md; Samal, P

    2012-01-01

    Starting with a brief introduction to excited-state density functional theory, we present our method of constructing modified local density approximated (MLDA) energy functionals for the excited states. We show that these functionals give accurate results for kinetic energy and exchange energy compared to the ground state LDA functionals. Further, with the inclusion of GGA correction, highly accurate total energies for excited states are obtained. We conclude with a brief discussion on the further direction of research that include the construction of correlation energy functional and exchange potential for excited states.

  19. A density functional theory study of new boron nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Zhao-Hua [Shijiazhuang Institute of Technology, Shijiazhuang (China); Xie, Zun [Hebei Normal Univ., Shijiazhuang (China). College of Physics Science and Information Engineering and Hebei Advanced Thin Films Lab.

    2017-07-01

    Using first-principles calculations, a series of new boron nanotubes (BNTs), which show various electronic properties, were theoretically predicted. Stable nanotubes with various chiral vectors and diameters can be formed by rolling up the boron sheet with relative stability [H. Tang and S. I. Beigi, Phys. Rev. B 82, 115412 (2010).]. By increasing the diameter for BNT, the stability is enhanced. The calculated density of states and band structures demonstrate that all the predicted BNTs are metallic, regardless of their diameter and chirality. The multicentre chemical bonds of the relatively stable boron sheet and BNTs are analysed using the deformation electron density. Within our study, the BNTs all have metallic conductive characteristics, in addition to having a low effective quality and high carrier concentration, which are very good nanoconductive material properties and could be combined to form high-power electrodes for lithium-ion batteries such as those used in many modern electronics.

  20. Combining first-principles and data modeling for the accurate prediction of the refractive index of organic polymers

    Science.gov (United States)

    Afzal, Mohammad Atif Faiz; Cheng, Chong; Hachmann, Johannes

    2018-06-01

    Organic materials with a high index of refraction (RI) are attracting considerable interest due to their potential application in optic and optoelectronic devices. However, most of these applications require an RI value of 1.7 or larger, while typical carbon-based polymers only exhibit values in the range of 1.3-1.5. This paper introduces an efficient computational protocol for the accurate prediction of RI values in polymers to facilitate in silico studies that can guide the discovery and design of next-generation high-RI materials. Our protocol is based on the Lorentz-Lorenz equation and is parametrized by the polarizability and number density values of a given candidate compound. In the proposed scheme, we compute the former using first-principles electronic structure theory and the latter using an approximation based on van der Waals volumes. The critical parameter in the number density approximation is the packing fraction of the bulk polymer, for which we have devised a machine learning model. We demonstrate the performance of the proposed RI protocol by testing its predictions against the experimentally known RI values of 112 optical polymers. Our approach to combine first-principles and data modeling emerges as both a successful and a highly economical path to determining the RI values for a wide range of organic polymers.