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

Theoretical and Empirical Descriptions of Thermospheric Density

Science.gov (United States)

Solomon, S. C.; Qian, L.

2004-12-01

The longest-term and most accurate overall description the density of the upper thermosphere is provided by analysis of change in the ephemeris of Earth-orbiting satellites. Empirical models of the thermosphere developed in part from these measurements can do a reasonable job of describing thermospheric properties on a climatological basis, but the promise of first-principles global general circulation models of the coupled thermosphere/ionosphere system is that a true high-resolution, predictive capability may ultimately be developed for thermospheric density. However, several issues are encountered when attempting to tune such models so that they accurately represent absolute densities as a function of altitude, and their changes on solar-rotational and solar-cycle time scales. Among these are the crucial ones of getting the heating rates (from both solar and auroral sources) right, getting the cooling rates right, and establishing the appropriate boundary conditions. However, there are several ancillary issues as well, such as the problem of registering a pressure-coordinate model onto an altitude scale, and dealing with possible departures from hydrostatic equilibrium in empirical models. Thus, tuning a theoretical model to match empirical climatology may be difficult, even in the absence of high temporal or spatial variation of the energy sources. We will discuss some of the challenges involved, and show comparisons of simulations using the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) to empirical model estimates of neutral thermosphere density and temperature. We will also show some recent simulations using measured solar irradiance from the TIMED/SEE instrument as input to the TIE-GCM.

Density functional theory of polydisperse fluid interfaces

International Nuclear Information System (INIS)

Baus, M.; Bellier-Castella, L.; Xu, H.

2002-01-01

Most colloids usually exhibit one or several polydispersities. A natural framework for the theoretical description of polydisperse systems is provided by the extension of density functional theory to 'continuous' mixtures. This will be illustrated here by the study of both the bulk and interfacial properties of a simple van der Waals model for a polydisperse colloidal fluid. (author)

Wood anatomical correlates with theoretical conductivity and wood density across China: evolutionary evidence of the functional differentiation of axial and radial parenchyma.

Science.gov (United States)

Zheng, Jingming; Martínez-Cabrera, Hugo I

2013-09-01

In recent years considerable effort has focused on linking wood anatomy and key ecological traits. Studies analysing large databases have described how these ecological traits vary as a function of wood anatomical traits related to conduction and support, but have not considered how these functions interact with cells involved in storage of water and carbohydrates (i.e. parenchyma cells). We analyzed, in a phylogenetic context, the functional relationship between cell types performing each of the three xylem functions (conduction, support and storage) and wood density and theoretical conductivity using a sample of approx. 800 tree species from China. Axial parenchyma and rays had distinct evolutionary correlation patterns. An evolutionary link was found between high conduction capacity and larger amounts of axial parenchyma that is probably related to water storage capacity and embolism repair, while larger amounts of ray tissue have evolved with increased mechanical support and reduced hydraulic capacity. In a phylogenetic principal component analysis this association of axial parenchyma with increased conduction capacity and rays with wood density represented orthogonal axes of variation. In multivariate space, however, the proportion of rays might be positively associated with conductance and negatively with wood density, indicating flexibility in these axes in species with wide rays. The findings suggest that parenchyma types may differ in function. The functional axes represented by different cell types were conserved across lineages, suggesting a significant role in the ecological strategies of the angiosperms.

A-centers in silicon studied with hybrid density functional theory

KAUST Repository

Wang, Hao; Chroneos, Alexander; Londos, C. A.; Schwingenschlö gl, Udo; Sgourou, E. N.

2013-01-01

Density functional theory employing hybrid functional is used to gain fundamental insight into the interaction of vacancies with oxygen interstitials to form defects known as A-centers in silicon. We calculate the formation energy of the defect with respect to the Fermi energy for all possible charge states. It is found that the neutral and doubly negatively charged A-centers dominate. The findings are analyzed in terms of the density of states and discussed in view of previous experimental and theoretical studies.

A-centers in silicon studied with hybrid density functional theory

KAUST Repository

Wang, Hao

2013-07-29

Density functional theory employing hybrid functional is used to gain fundamental insight into the interaction of vacancies with oxygen interstitials to form defects known as A-centers in silicon. We calculate the formation energy of the defect with respect to the Fermi energy for all possible charge states. It is found that the neutral and doubly negatively charged A-centers dominate. The findings are analyzed in terms of the density of states and discussed in view of previous experimental and theoretical studies.

On the evolution of the density probability density function in strongly self-gravitating systems

International Nuclear Information System (INIS)

Girichidis, Philipp; Konstandin, Lukas; Klessen, Ralf S.; Whitworth, Anthony P.

2014-01-01

The time evolution of the probability density function (PDF) of the mass density is formulated and solved for systems in free-fall using a simple approximate function for the collapse of a sphere. We demonstrate that a pressure-free collapse results in a power-law tail on the high-density side of the PDF. The slope quickly asymptotes to the functional form P V (ρ)∝ρ –1.54 for the (volume-weighted) PDF and P M (ρ)∝ρ –0.54 for the corresponding mass-weighted distribution. From the simple approximation of the PDF we derive analytic descriptions for mass accretion, finding that dynamically quiet systems with narrow density PDFs lead to retarded star formation and low star formation rates (SFRs). Conversely, strong turbulent motions that broaden the PDF accelerate the collapse causing a bursting mode of star formation. Finally, we compare our theoretical work with observations. The measured SFRs are consistent with our model during the early phases of the collapse. Comparison of observed column density PDFs with those derived from our model suggests that observed star-forming cores are roughly in free-fall.

Density functional theory a practical introduction

CERN Document Server

Sholl, David

2009-01-01

Demonstrates how anyone in math, science, and engineering can master DFT calculations Density functional theory (DFT) is one of the most frequently used computational tools for studying and predicting the properties of isolated molecules, bulk solids, and material interfaces, including surfaces. Although the theoretical underpinnings of DFT are quite complicated, this book demonstrates that the basic concepts underlying the calculations are simple enough to be understood by anyone with a background in chemistry, physics, engineering, or mathematics. The authors show how the widespread availability of powerful DFT codes makes it possible for students and researchers to apply this important computational technique to a broad range of fundamental and applied problems. Density Functional Theory: A Practical Introduction offers a concise, easy-to-follow introduction to the key concepts and practical applications of DFT, focusing on plane-wave DFT. The authors have many years of experience introducing DFT to studen...

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

SURFACE SYMMETRY ENERGY OF NUCLEAR ENERGY DENSITY FUNCTIONALS

Energy Technology Data Exchange (ETDEWEB)

Nikolov, N; Schunck, N; Nazarewicz, W; Bender, M; Pei, J

2010-12-20

We study the bulk deformation properties of the Skyrme nuclear energy density functionals. Following simple arguments based on the leptodermous expansion and liquid drop model, we apply the nuclear density functional theory to assess the role of the surface symmetry energy in nuclei. To this end, we validate the commonly used functional parametrizations against the data on excitation energies of superdeformed band-heads in Hg and Pb isotopes, and fission isomers in actinide nuclei. After subtracting shell effects, the results of our self-consistent calculations are consistent with macroscopic arguments and indicate that experimental data on strongly deformed configurations in neutron-rich nuclei are essential for optimizing future nuclear energy density functionals. The resulting survey provides a useful benchmark for further theoretical improvements. Unlike in nuclei close to the stability valley, whose macroscopic deformability hangs on the balance of surface and Coulomb terms, the deformability of neutron-rich nuclei strongly depends on the surface-symmetry energy; hence, its proper determination is crucial for the stability of deformed phases of the neutron-rich matter and description of fission rates for r-process nucleosynthesis.

Theoretical foundations for reconstruction of the materials density by means of two-energy radiography

International Nuclear Information System (INIS)

Naydenov, S.V.; Ryzhikov, V.

2003-01-01

In non-destructive testing of building constructions, concrete structures, granular and powder materials, mixtures, alloys, etc. it is often very important to determine their mass and/or surface density. Density decreases or increases with respect to the standard values can substantially lower the quality of functional materials, as well strength of joints and constructions. In this paper, we have shown theoretically that the most complete solution of the inverse problem of quantitative reconstruction of the density profile can be given by means of two-energy radiography. A general expressions has been obtained for the surface density of an arbitrary material. Theoretically, the accuracy of the method is within several percent. An important point is that the approach proposed does not require any preliminary knowledge about physical or chemical composition of the tested object. This allows the use of the developed algorithm for universal testing of various construction objects in building and industry, including situations of prolonged service, when the chemical structure can get substantially changed. Among possible applications of the new method there are control testing in building and building industry, railway and vehicle transport, diagnostics of oil and gas pipes, hydrotechnical constructions (dams), etc

An experimental and theoretical study of molecular structure and vibrational spectra of 2-methylphenyl boronic acid by density functional theory calculations

Science.gov (United States)

Hiremath, Sudhir M.; Hiremath, C. S.; Khemalapure, S. S.; Patil, N. R.

2018-05-01

This paper reports the experimental and theoretical study on the structure and vibrations of 2-Methylphenyl boronic acid (2MPBA). The different spectroscopic techniques such as FT-IR (4000-400 cm-1) and FT-Raman (4000-50 cm-1) of the title molecule in the solid phase were recorded. The geometry of the molecule was fully optimized using density functional theory (DFT) (B3LYP) with 6-311++G(d, p) basis set calculations. The vibrational wavenumbers were also corrected with scale factor to take better results for the calculated data. Vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the potential energy distribution (PED) of the vibrational modes obtained from VEDA 4 program. The calculated wavenumbers showed the best agreement with the experimental results. Whereas, it is observed that, the theoretical frequencies are more than the experimental one for O-H stretching vibration modes of the title molecule.

Dynamic density functional theory of solid tumor growth: Preliminary models

Directory of Open Access Journals (Sweden)

Arnaud Chauviere

2012-03-01

Full Text Available Cancer is a disease that can be seen as a complex system whose dynamics and growth result from nonlinear processes coupled across wide ranges of spatio-temporal scales. The current mathematical modeling literature addresses issues at various scales but the development of theoretical methodologies capable of bridging gaps across scales needs further study. We present a new theoretical framework based on Dynamic Density Functional Theory (DDFT extended, for the first time, to the dynamics of living tissues by accounting for cell density correlations, different cell types, phenotypes and cell birth/death processes, in order to provide a biophysically consistent description of processes across the scales. We present an application of this approach to tumor growth.

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

Density functional and theoretical study of the temperature and pressure dependency of the plasmon energy of solids

International Nuclear Information System (INIS)

Attarian Shandiz, M.; Gauvin, R.

2014-01-01

The temperature and pressure dependency of the volume plasmon energy of solids was investigated by density functional theory calculations. The volume change of crystal is the major factor responsible for the variation of valence electron density and plasmon energy in the free electron model. Hence, to introduce the effect of temperature and pressure for the density functional theory calculations of plasmon energy, the temperature and pressure dependency of lattice parameter was used. Also, by combination of the free electron model and the equation of state based on the pseudo-spinodal approach, the temperature and pressure dependency of the plasmon energy was modeled. The suggested model is in good agreement with the results of density functional theory calculations and available experimental data for elements with the free electron behavior.

Recent progress in orbital-free density functional theory (recent advances in computational chemistry)

CERN Document Server

Wesolowski, Tomasz A

2013-01-01

This is a comprehensive overview of state-of-the-art computational methods based on orbital-free formulation of density functional theory completed by the most recent developments concerning the exact properties, approximations, and interpretations of the relevant quantities in density functional theory. The book is a compilation of contributions stemming from a series of workshops which had been taking place since 2002. It not only chronicles many of the latest developments but also summarises some of the more significant ones. The chapters are mainly reviews of sub-domains but also include original research. Readership: Graduate students, academics and researchers in computational chemistry. Atomic & molecular physicists, theoretical physicists, theoretical chemists, physical chemists and chemical physicists.

KIDS Nuclear Energy Density Functional: 1st Application in Nuclei

Science.gov (United States)

Gil, Hana; Papakonstantinou, Panagiota; Hyun, Chang Ho; Oh, Yongseok

We apply the KIDS (Korea: IBS-Daegu-Sungkyunkwan) nuclear energy density functional model, which is based on the Fermi momentum expansion, to the study of properties of lj-closed nuclei. The parameters of the model are determined by the nuclear properties at the saturation density and theoretical calculations on pure neutron matter. For applying the model to the study of nuclei, we rely on the Skyrme force model, where the Skyrme force parameters are determined through the KIDS energy density functional. Solving Hartree-Fock equations, we obtain the energies per particle and charge radii of closed magic nuclei, namely, 16O, 28O, 40Ca, 48Ca, 60Ca, 90Zr, 132Sn, and 208Pb. The results are compared with the observed data and further improvement of the model is shortly mentioned.

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.

Density Functional Methods for Shock Physics and High Energy Density Science

Science.gov (United States)

Desjarlais, Michael

2017-06-01

Molecular dynamics with density functional theory has emerged over the last two decades as a powerful and accurate framework for calculating thermodynamic and transport properties with broad application to dynamic compression, high energy density science, and warm dense matter. These calculations have been extensively validated against shock and ramp wave experiments, are a principal component of high-fidelity equation of state generation, and are having wide-ranging impacts on inertial confinement fusion, planetary science, and shock physics research. In addition to thermodynamic properties, phase boundaries, and the equation of state, one also has access to electrical conductivity, thermal conductivity, and lower energy optical properties. Importantly, all these properties are obtained within the same theoretical framework and are manifestly consistent. In this talk I will give a brief history and overview of molecular dynamics with density functional theory and its use in calculating a wide variety of thermodynamic and transport properties for materials ranging from ambient to extreme conditions and with comparisons to experimental data. I will also discuss some of the limitations and difficulties, as well as active research areas. Sandia 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.

Magnetic behavior study of samarium nitride using density functional theory

Science.gov (United States)

Som, Narayan N.; Mankad, Venu H.; Dabhi, Shweta D.; Patel, Anjali; Jha, Prafulla K.

2018-02-01

In this work, the state-of-art density functional theory is employed to study the structural, electronic and magnetic properties of samarium nitride (SmN). We have performed calculation for both ferromagnetic and antiferromagnetic states in rock-salt phase. The calculated results of optimized lattice parameter and magnetic moment agree well with the available experimental and theoretical values. From energy band diagram and electronic density of states, we observe a half-metallic behaviour in FM phase of rock salt SmN in while metallicity in AFM I and AFM III phases. We present and discuss our current understanding of the possible half-metallicity together with the magnetic ordering in SmN. The calculated phonon dispersion curves shows dynamical stability of the considered structures. The phonon density of states and Eliashberg functional have also been analysed to understand the superconductivity in SmN.

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

A theoretical-electron-density databank using a model of real and virtual spherical atoms.

Science.gov (United States)

Nassour, Ayoub; Domagala, Slawomir; Guillot, Benoit; Leduc, Theo; Lecomte, Claude; Jelsch, Christian

2017-08-01

A database describing the electron density of common chemical groups using combinations of real and virtual spherical atoms is proposed, as an alternative to the multipolar atom modelling of the molecular charge density. Theoretical structure factors were computed from periodic density functional theory calculations on 38 crystal structures of small molecules and the charge density was subsequently refined using a density model based on real spherical atoms and additional dummy charges on the covalent bonds and on electron lone-pair sites. The electron-density parameters of real and dummy atoms present in a similar chemical environment were averaged on all the molecules studied to build a database of transferable spherical atoms. Compared with the now-popular databases of transferable multipolar parameters, the spherical charge modelling needs fewer parameters to describe the molecular electron density and can be more easily incorporated in molecular modelling software for the computation of electrostatic properties. The construction method of the database is described. In order to analyse to what extent this modelling method can be used to derive meaningful molecular properties, it has been applied to the urea molecule and to biotin/streptavidin, a protein/ligand complex.

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.

What is the best density functional to describe water clusters: evaluation of widely used density functionals with various basis sets for (H2O)n (n = 1-10)

Czech Academy of Sciences Publication Activity Database

Li, F.; Wang, L.; Zhao, J.; Xie, J. R. H.; Riley, Kevin Eugene; Chen, Z.

2011-01-01

Roč. 130, 2/3 (2011), s. 341-352 ISSN 1432-881X Institutional research plan: CEZ:AV0Z40550506 Keywords : water cluster * density functional theory * MP2 . CCSD(T) * basis set * relative energies Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.162, year: 2011

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

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

Bridge density functional approximation for non-uniform hard core repulsive Yukawa fluid

International Nuclear Information System (INIS)

Zhou Shiqi

2008-01-01

In this work, a bridge density functional approximation (BDFA) (J. Chem. Phys. 112, 8079 (2000)) for a non-uniform hard-sphere fluid is extended to a non-uniform hard-core repulsive Yukawa (HCRY) fluid. It is found that the choice of a bulk bridge functional approximation is crucial for both a uniform HCRY fluid and a non-uniform HCRY fluid. A new bridge functional approximation is proposed, which can accurately predict the radial distribution function of the bulk HCRY fluid. With the new bridge functional approximation and its associated bulk second order direct correlation function as input, the BDFA can be used to well calculate the density profile of the HCRY fluid subjected to the influence of varying external fields, and the theoretical predictions are in good agreement with the corresponding simulation data. The calculated results indicate that the present BDFA captures quantitatively the phenomena such as the coexistence of solid-like high density phase and low density gas phase, and the adsorption properties of the HCRY fluid, which qualitatively differ from those of the fluids combining both hard-core repulsion and an attractive tail. (condensed matter: structure, thermal and mechanical properties)

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

Density functional study of the bonding in small silicon clusters

International Nuclear Information System (INIS)

Fournier, R.; Sinnott, S.B.; DePristo, A.E.

1992-01-01

We report the ground electronic state, equilibrium geometry, vibrational frequencies, and binding energy for various isomers of Si n (n = 2--8) obtained with the linear combination of atomic orbitals-density functional method. We used both a local density approximation approach and one with gradient corrections. Our local density approximation results concerning the relative stability of electronic states and isomers are in agreement with Hartree--Fock and Moller--Plesset (MP2) calculations [K. Raghavachari and C. M. Rohlfing, J. Chem. Phys. 89, 2219 (1988)]. The binding energies calculated with the gradient corrected functional are in good agreement with experiment (Si 2 and Si 3 ) and with the best theoretical estimates. Our analysis of the bonding reveals two limiting modes of bonding and classes of silicon clusters. One class of clusters is characterized by relatively large s atomic populations and a large number of weak bonds, while the other class of clusters is characterized by relatively small s atomic populations and a small number of strong bonds

Ionization Potentials of Chemical Warfare Agents and Related Compounds Determined with Density Functional Theory

National Research Council Canada - National Science Library

Wright, J

2000-01-01

...) agents at contaminated sites. Reported herein are theoretical ionization potentials for CW agents and their related compounds calculated using density functional theory at the B3LYP/6-311+G(2d,p) level of theory...

Melting slope of MgO from molecular dynamics and density functional theory

Science.gov (United States)

Tangney, Paul; Scandolo, Sandro

2009-09-01

We combine density functional theory (DFT) with molecular dynamics simulations based on an accurate atomistic force field to calculate the pressure derivative of the melting temperature of magnesium oxide at ambient pressure—a quantity for which a serious disagreement between theory and experiment has existed for almost 15 years. We find reasonable agreement with previous DFT results and with a very recent experimental determination of the slope. We pay particular attention to areas of possible weakness in theoretical calculations and conclude that the long-standing discrepancy with experiment could only be explained by a dramatic failure of existing density functionals or by flaws in the original experiment.

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.

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

Density-dependence of functional spiking networks in vitro

Energy Technology Data Exchange (ETDEWEB)

Ham, Michael I [Los Alamos National Laboratory; Gintautuas, Vadas [Los Alamos National Laboratory; Rodriguez, Marko A [Los Alamos National Laboratory; Bettencourt, Luis M A [Los Alamos National Laboratory; Bennett, Ryan [UNIV OF NORTH TEXAS; Santa Maria, Cara L [UNIV OF NORTH TEXAS

2008-01-01

During development, the mammalian brain differentiates into specialized regions with unique functional abilities. While many factors contribute to this functional specialization, we explore the effect neuronal density can have on neuronal interactions. Two types of networks, dense (50,000 neurons and glia support cells) and sparse (12,000 neurons and glia support cells), are studied. A competitive first response model is applied to construct activation graphs that represent pairwise neuronal interactions. By observing the evolution of these graphs during development in vitro we observe that dense networks form activation connections earlier than sparse networks, and that link-!llltropy analysis of the resulting dense activation graphs reveals that balanced directional connections dominate. Information theoretic measures reveal in addition that early functional information interactions (of order 3) are synergetic in both dense and sparse networks. However, during development in vitro, such interactions become redundant in dense, but not sparse networks. Large values of activation graph link-entropy correlate strongly with redundant ensembles observed in the dense networks. Results demonstrate differences between dense and sparse networks in terms of informational groups, pairwise relationships, and activation graphs. These differences suggest that variations in cell density may result in different functional specialization of nervous system tissue also in vivo.

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

transformation (local-scaling of coordinates proceeds through density transformation) and so, because these functionals are constructed from prototype N-particle wavefunctions, the ensuing density functionals already have built-in N-representability conditions. This theory is presented in great detail with the purpose of illustrating an alternative way to HKS-DFT which could be used to improve the construction of HKS-DFT functionals. Let us clearly indicate, however, that although appealing from a theoretical point of view, the actual application of LS-DFT to large systems has not taken place mostly because of technical difficulties. Thus, our aim in introducing this theory is to foster a better understanding of its foundations with the hope that it may promote a cross-hybridization with the already existing approaches. Also, to complete our previous discussion on symmetry, in particular, spin-symmetry, we discuss this issue from the perspective of LS-DFT. Finally, in Section  6, we discuss dispersion molecular forces emphasizing their relevance to DFT approaches.

General framework for fluctuating dynamic density functional theory

Science.gov (United States)

Durán-Olivencia, Miguel A.; Yatsyshin, Peter; Goddard, Benjamin D.; Kalliadasis, Serafim

2017-12-01

We introduce a versatile bottom-up derivation of a formal theoretical framework to describe (passive) soft-matter systems out of equilibrium subject to fluctuations. We provide a unique connection between the constituent-particle dynamics of real systems and the time evolution equation of their measurable (coarse-grained) quantities, such as local density and velocity. The starting point is the full Hamiltonian description of a system of colloidal particles immersed in a fluid of identical bath particles. Then, we average out the bath via Zwanzig’s projection-operator techniques and obtain the stochastic Langevin equations governing the colloidal-particle dynamics. Introducing the appropriate definition of the local number and momentum density fields yields a generalisation of the Dean-Kawasaki (DK) model, which resembles the stochastic Navier-Stokes description of a fluid. Nevertheless, the DK equation still contains all the microscopic information and, for that reason, does not represent the dynamical law of observable quantities. We address this controversial feature of the DK description by carrying out a nonequilibrium ensemble average. Adopting a natural decomposition into local-equilibrium and nonequilibrium contribution, where the former is related to a generalised version of the canonical distribution, we finally obtain the fluctuating-hydrodynamic equation governing the time-evolution of the mesoscopic density and momentum fields. Along the way, we outline the connection between the ad hoc energy functional introduced in previous DK derivations and the free-energy functional from classical density-functional theory. The resultant equation has the structure of a dynamical density-functional theory (DDFT) with an additional fluctuating force coming from the random interactions with the bath. We show that our fluctuating DDFT formalism corresponds to a particular version of the fluctuating Navier-Stokes equations, originally derived by Landau and Lifshitz

Experimental nuclear level densities and γ-ray strength functions in Sc and V isotopes

International Nuclear Information System (INIS)

Larsen, A. C.; Guttormsen, M.; Ingebretsen, F.; Messelt, S.; Rekstad, J.; Siem, S.; Syed, N. U. H.; Chankova, R.; Loennroth, T.; Schiller, A.; Voinov, A.

2008-01-01

The nuclear physics group at the Oslo Cyclotron Laboratory has developed a method to extract nuclear level density and γ-ray strength function from first-generation γ-ray spectra. This method is applied on the nuclei 44,45 Sc and 50,51 V in this work. The experimental level densities of 44,45 Sc are compared to calculated level densities using a microscopic model based on BCS quasiparticles within the Nilsson level scheme. The γ-ray strength functions are also compared to theoretical expectations, showing an unexpected enhancement of the γ-ray strength for low γ energies (E γ ≤3 MeV) in all the isotopes studied here. The physical origin of this enhancement is not yet understood

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 ...

Computational Study of Chemical Reactivity Using Information-Theoretic Quantities from Density Functional Reactivity Theory for Electrophilic Aromatic Substitution Reactions.

Science.gov (United States)

Wu, Wenjie; Wu, Zemin; Rong, Chunying; Lu, Tian; Huang, Ying; Liu, Shubin

2015-07-23

The electrophilic aromatic substitution for nitration, halogenation, sulfonation, and acylation is a vastly important category of chemical transformation. Its reactivity and regioselectivity is predominantly determined by nucleophilicity of carbon atoms on the aromatic ring, which in return is immensely influenced by the group that is attached to the aromatic ring a priori. In this work, taking advantage of recent developments in quantifying nucleophilicity (electrophilicity) with descriptors from the information-theoretic approach in density functional reactivity theory, we examine the reactivity properties of this reaction system from three perspectives. These include scaling patterns of information-theoretic quantities such as Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy and information gain at both molecular and atomic levels, quantitative predictions of the barrier height with both Hirshfeld charge and information gain, and energetic decomposition analyses of the barrier height for the reactions. To that end, we focused in this work on the identity reaction of the monosubstituted-benzene molecule reacting with hydrogen fluoride using boron trifluoride as the catalyst in the gas phase. We also considered 19 substituting groups, 9 of which are ortho/para directing and the other 9 meta directing, besides the case of R = -H. Similar scaling patterns for these information-theoretic quantities found for stable species elsewhere were disclosed for these reactions systems. We also unveiled novel scaling patterns for information gain at the atomic level. The barrier height of the reactions can reliably be predicted by using both the Hirshfeld charge and information gain at the regioselective carbon atom. The energy decomposition analysis ensued yields an unambiguous picture about the origin of the barrier height, where we showed that it is the electrostatic interaction that plays the dominant role, while the roles played by exchange-correlation and

On the contact values of the density profiles in an electric double layer using density functional theory

Directory of Open Access Journals (Sweden)

L.B. Bhuiyan

2012-06-01

Full Text Available A recently proposed, local second contact value theorem [Henderson D., Boda D., J. Electroanal. Chem., 2005, Vol. 582, 16] for the charge profile of an electric double layer is used in conjunction with existing Monte Carlo data from the literature to assess the contact behavior of the electrode-ion distributions predicted by the density functional theory. The results for the contact values of the co- and counterion distributions and their product are obtained for the symmetric valency, restricted primitive model planar double layer for a range of electrolyte concentrations and temperatures. Overall the theoretical results satisfy the second contact value theorem reasonably well the agreement with the simulations being semi-quantitative or better. The product of the co- and counterion contact values as a function of the electrode surface charge density is qualitative with the simulations with increasing deviations at higher concentrations.

Description of odd-mass nuclei by multi-reference energy density functional methods

International Nuclear Information System (INIS)

Bally, B.

2014-01-01

In this work, we are interested in the treatment of odd-mass atomic nuclei in energy density functional (EDF) models. More precisely, the goal of this thesis is to develop and to apply to odd-mass nuclei, the theoretical extensions of the EDF method that are: first, the projection technique, and secondly the configuration mixing by the generator coordinate method (GCM). These two extensions are part of the so-called multi-reference energy density functional (MR-EDF) formalism and allow one to take into account, within an EDF context, the 'beyond-mean-field' correlations between the nucleons forming the nucleus. Until now, the MR-EDF formalism has been applied, in its fully-fledged version, only to the calculation of even-even nuclei. In this thesis, we want to demonstrate the applicability of such a model also for the description of odd-mass nuclei. In the first part of this thesis, we describe the theoretical formalism of the EDF models, giving particular attention to the treatment of symmetries within our approach. In the second part of the manuscript, we apply our model to the nucleus 25 Mg and investigate different aspects of the method (e.g. numerical accuracy, convergence of the configuration mixing, comparison to known experimental data). The results obtained in this work are encouraging and demonstrate the potential of our approach for theoretical nuclear structure calculations. (author)

Density-functional study of the CO adsorption on ferromagnetic Co(0001) and Co(111) surfaces

Czech Academy of Sciences Publication Activity Database

Pick, Štěpán

2007-01-01

Roč. 601, č. 23 (2007), s. 5571-5575 ISSN 0039-6028 Institutional research plan: CEZ:AV0Z40400503 Keywords : density functional calculation * chemisorption * magnetic films Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.855, year: 2007

Density-functional study of the CO adsorption on the ferromagnetic fcc Co(001) film surface

Czech Academy of Sciences Publication Activity Database

Pick, Štěpán

2010-01-01

Roč. 604, 3-4 (2010), s. 265-268 ISSN 0039-6028 Institutional research plan: CEZ:AV0Z40400503 Keywords : Density functional calculations * chemisorption * magnetic films Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.010, year: 2010

Time-dependent density functional theory (TD-DFT) coupled with reference interaction site model self-consistent field explicitly including spatial electron density distribution (RISM-SCF-SEDD)

Energy Technology Data Exchange (ETDEWEB)

Yokogawa, D., E-mail: d.yokogawa@chem.nagoya-u.ac.jp [Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602 (Japan); Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya 464-8602 (Japan)

2016-09-07

Theoretical approach to design bright bio-imaging molecules is one of the most progressing ones. However, because of the system size and computational accuracy, the number of theoretical studies is limited to our knowledge. To overcome the difficulties, we developed a new method based on reference interaction site model self-consistent field explicitly including spatial electron density distribution and time-dependent density functional theory. We applied it to the calculation of indole and 5-cyanoindole at ground and excited states in gas and solution phases. The changes in the optimized geometries were clearly explained with resonance structures and the Stokes shift was correctly reproduced.

Theoretical investigation of cyromazine tautomerism using density functional theory and Møller–Plesset perturbation theory methods

Science.gov (United States)

A computational chemistry analysis of six unique tautomers of cyromazine, a pesticide used for fly control, was performed with density functional theory (DFT) and canonical second order Møller–Plesset perturbation theory (MP2) methods to gain insight into the contributions of molecular structure to ...

Density functional theory and multiscale materials modeling

Indian Academy of Sciences (India)

One of the vital ingredients in the theoretical tools useful in materials modeling at all the length scales of interest is the concept of density. In the microscopic length scale, it is the electron density that has played a major role in providing a deeper understanding of chemical binding in atoms, molecules and solids.

Applications of the Conceptual Density Functional Theory Indices to Organic Chemistry Reactivity.

Science.gov (United States)

Domingo, Luis R; Ríos-Gutiérrez, Mar; Pérez, Patricia

2016-06-09

Theoretical reactivity indices based on the conceptual Density Functional Theory (DFT) have become a powerful tool for the semiquantitative study of organic reactivity. A large number of reactivity indices have been proposed in the literature. Herein, global quantities like the electronic chemical potential μ, the electrophilicity ω and the nucleophilicity N indices, and local condensed indices like the electrophilic P k + and nucleophilic P k - Parr functions, as the most relevant indices for the study of organic reactivity, are discussed.

A theoretical study of lithium-doped gallium clusters by density functional theory

Energy Technology Data Exchange (ETDEWEB)

Sentuerk, Suekrue; Ekincioglu, Yavuz [Dumlupinar Univ., Kutahya (Turkey). Dept. of Physics

2012-05-15

The geometrical structures, stabilities, and electronic properties of Ga{sub n}Li (n = 1-13) clusters were investigated within the density functional theory (DFT). The impurity lithium atom enhances the stability of Ga{sub n}Li (n = 1-13) clusters, especially Ga{sub n}Li (n = 9-13) compared to Ga{sub n} (n = 9-14), that is at either apex position or side position. The dissociation energy, second-order energy differences, and the energy gaps between highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) indicate that the Ga{sub 7}Li, Ga{sub 9}Li, and Ga{sub 11}Li clusters are more stable within the studied cluster range. Moreover, the variation of the average bond length of Ga - Li is due to the surface effect, and the binding strength increases resulting from the increase of charge amount. (orig.)

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.

Covariant density functional theory for nuclear matter

Energy Technology Data Exchange (ETDEWEB)

Badarch, U.

2007-07-01

The present thesis is organized as follows. In Chapter 2 we study the Nucleon-Nucleon (NN) interaction in Dirac-Brueckner (DB) approach. We start by considering the NN interaction in free-space in terms of the Bethe-Salpeter (BS) equation to the meson exchange potential model. Then we present the DB approach for nuclear matter by extending the BS equation for the in-medium NN interaction. From the solution of the three-dimensional in-medium BS equation, we derive the DB self-energies and total binding energy which are the main results of the DB approach, which we later incorporate in the field theoretical calculation of the nuclear equation of state. In Chapter 3, we introduce the basic concepts of density functional theory in the context of Quantum Hadrodynamics (QHD-I). We reach the main point of this work in Chapter 4 where we introduce the DDRH approach. In the DDRH theory, the medium dependence of the meson-nucleon vertices is expressed as functionals of the baryon field operators. Because of the complexities of the operator-valued functionals we decide to use the mean-field approximation. In Chapter 5, we contrast microscopic and phenomenological approaches to extracting density dependent meson-baryon vertices. Chapter 6 gives the results of our studies of the EOS of infinite nuclear matter in detail. Using formulas derived in Chapters 4 and 5 we calculate the properties of symmetric and asymmetric nuclear matter and pure neutron matter. (orig.)

Covariant density functional theory for nuclear matter

International Nuclear Information System (INIS)

Badarch, U.

2007-01-01

The present thesis is organized as follows. In Chapter 2 we study the Nucleon-Nucleon (NN) interaction in Dirac-Brueckner (DB) approach. We start by considering the NN interaction in free-space in terms of the Bethe-Salpeter (BS) equation to the meson exchange potential model. Then we present the DB approach for nuclear matter by extending the BS equation for the in-medium NN interaction. From the solution of the three-dimensional in-medium BS equation, we derive the DB self-energies and total binding energy which are the main results of the DB approach, which we later incorporate in the field theoretical calculation of the nuclear equation of state. In Chapter 3, we introduce the basic concepts of density functional theory in the context of Quantum Hadrodynamics (QHD-I). We reach the main point of this work in Chapter 4 where we introduce the DDRH approach. In the DDRH theory, the medium dependence of the meson-nucleon vertices is expressed as functionals of the baryon field operators. Because of the complexities of the operator-valued functionals we decide to use the mean-field approximation. In Chapter 5, we contrast microscopic and phenomenological approaches to extracting density dependent meson-baryon vertices. Chapter 6 gives the results of our studies of the EOS of infinite nuclear matter in detail. Using formulas derived in Chapters 4 and 5 we calculate the properties of symmetric and asymmetric nuclear matter and pure neutron matter. (orig.)

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.

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.

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.

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

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

Electronic states of aryl radical functionalized graphenes: Density functional theory study

Science.gov (United States)

Tachikawa, Hiroto; Kawabata, Hiroshi

2016-06-01

Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz) n (n = 1-4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR-(Bz) n (n = 1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol-1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol-1. The electronic states of GR-(Bz) n were examined on the basis of theoretical results.

VV and VO2 defects in silicon studied with hybrid density functional theory

KAUST Repository

Christopoulos, Stavros Richard G

2014-12-07

The formation of VO (A-center), VV and VO2 defects in irradiated Czochralski-grown silicon (Si) is of technological importance. Recent theoretical studies have examined the formation and charge states of the A-center in detail. Here we use density functional theory employing hybrid functionals to analyze the formation of VV and VO2 defects. The formation energy as a function of the Fermi energy is calculated for all possible charge states. For the VV and VO2 defects double negatively charged and neutral states dominate, respectively.

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.

Uncertainty quantification for nuclear density functional theory and information content of new measurements.

Science.gov (United States)

McDonnell, J D; Schunck, N; Higdon, D; Sarich, J; Wild, S M; Nazarewicz, W

2015-03-27

Statistical tools of uncertainty quantification can be used to assess the information content of measured observables with respect to present-day theoretical models, to estimate model errors and thereby improve predictive capability, to extrapolate beyond the regions reached by experiment, and to provide meaningful input to applications and planned measurements. To showcase new opportunities offered by such tools, we make a rigorous analysis of theoretical statistical uncertainties in nuclear density functional theory using Bayesian inference methods. By considering the recent mass measurements from the Canadian Penning Trap at Argonne National Laboratory, we demonstrate how the Bayesian analysis and a direct least-squares optimization, combined with high-performance computing, can be used to assess the information content of the new data with respect to a model based on the Skyrme energy density functional approach. Employing the posterior probability distribution computed with a Gaussian process emulator, we apply the Bayesian framework to propagate theoretical statistical uncertainties in predictions of nuclear masses, two-neutron dripline, and fission barriers. Overall, we find that the new mass measurements do not impose a constraint that is strong enough to lead to significant changes in the model parameters. The example discussed in this study sets the stage for quantifying and maximizing the impact of new measurements with respect to current modeling and guiding future experimental efforts, thus enhancing the experiment-theory cycle in the scientific method.

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.

Theoretical model of the density of states of random binary alloys

International Nuclear Information System (INIS)

Zekri, N.; Brezini, A.

1991-09-01

A theoretical formulation of the density of states for random binary alloys is examined based on a mean field treatment. The present model includes both diagonal and off-diagonal disorder and also short-range order. Extensive results are reported for various concentrations and compared to other calculations. (author). 22 refs, 6 figs

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.

Theoretical Model for Volume Fraction of UC, 235U Enrichment, and Effective Density of Final U 10Mo Alloy

Energy Technology Data Exchange (ETDEWEB)

Devaraj, Arun [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); Prabhakaran, Ramprashad [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); Joshi, Vineet V. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); Hu, Shenyang Y. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); McGarrah, Eric J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); Lavender, Curt A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)

2016-04-12

The purpose of this document is to provide a theoretical framework for (1) estimating uranium carbide (UC) volume fraction in a final alloy of uranium with 10 weight percent molybdenum (U-10Mo) as a function of final alloy carbon concentration, and (2) estimating effective ²³⁵U enrichment in the U-10Mo matrix after accounting for loss of ²³⁵U in forming UC. This report will also serve as a theoretical baseline for effective density of as-cast low-enriched U-10Mo alloy. Therefore, this report will serve as the baseline for quality control of final alloy carbon content

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.

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.

Polymer density functional theory approach based on scaling second-order direct correlation function.

Science.gov (United States)

Zhou, Shiqi

2006-06-01

A second-order direct correlation function (DCF) from solving the polymer-RISM integral equation is scaled up or down by an equation of state for bulk polymer, the resultant scaling second-order DCF is in better agreement with corresponding simulation results than the un-scaling second-order DCF. When the scaling second-order DCF is imported into a recently proposed LTDFA-based polymer DFT approach, an originally associated adjustable but mathematically meaningless parameter now becomes mathematically meaningful, i.e., the numerical value lies now between 0 and 1. When the adjustable parameter-free version of the LTDFA is used instead of the LTDFA, i.e., the adjustable parameter is fixed at 0.5, the resultant parameter-free version of the scaling LTDFA-based polymer DFT is also in good agreement with the corresponding simulation data for density profiles. The parameter-free version of the scaling LTDFA-based polymer DFT is employed to investigate the density profiles of a freely jointed tangent hard sphere chain near a variable sized central hard sphere, again the predictions reproduce accurately the simulational results. Importance of the present adjustable parameter-free version lies in its combination with a recently proposed universal theoretical way, in the resultant formalism, the contact theorem is still met by the adjustable parameter associated with the theoretical way.

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.

Spectral function from Reduced Density Matrix Functional Theory

Science.gov (United States)

Romaniello, Pina; di Sabatino, Stefano; Berger, Jan A.; Reining, Lucia

2015-03-01

In this work we focus on the calculation of the spectral function, which determines, for example, photoemission spectra, from reduced density matrix functional theory. Starting from its definition in terms of the one-body Green's function we derive an expression for the spectral function that depends on the natural occupation numbers and on an effective energy which accounts for all the charged excitations. This effective energy depends on the two-body as well as higher-order density matrices. Various approximations to this expression are explored by using the exactly solvable Hubbard chains.

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.

Exchange coupling and magnetic anisotropy of exchanged-biased quantum tunnelling single-molecule magnet Ni3Mn2 complexes using theoretical methods based on Density Functional Theory.

Science.gov (United States)

Gómez-Coca, Silvia; Ruiz, Eliseo

2012-03-07

The magnetic properties of a new family of single-molecule magnet Ni(3)Mn(2) complexes were studied using theoretical methods based on Density Functional Theory (DFT). The first part of this study is devoted to analysing the exchange coupling constants, focusing on the intramolecular as well as the intermolecular interactions. The calculated intramolecular J values were in excellent agreement with the experimental data, which show that all the couplings are ferromagnetic, leading to an S = 7 ground state. The intermolecular interactions were investigated because the two complexes studied do not show tunnelling at zero magnetic field. Usually, this exchange-biased quantum tunnelling is attributed to the presence of intermolecular interactions calculated with the help of theoretical methods. The results indicate the presence of weak intermolecular antiferromagnetic couplings that cannot explain the ferromagnetic value found experimentally for one of the systems. In the second part, the goal is to analyse magnetic anisotropy through the calculation of the zero-field splitting parameters (D and E), using DFT methods including the spin-orbit effect.

UV-Vis optoelectronic properties of α-SnWO4: A comparative experimental and density functional theory based study

KAUST Repository

Ziani, Ahmed

2015-09-03

We report a combined experimental and theoretical study on the optoelectronic properties of α-SnWO4 for UV-Vis excitation. The experimentally measured values for thin films were systematically compared with high-accuracy density functional theory and density functional perturbation theory using the HSE06 functional. The α-SnWO4 material shows an indirect bandgap of 1.52 eV with high absorption coefficient in the visible-light range (>2 × 105 cm−1). The results show relatively high dielectric constant (>30) and weak diffusion properties (large effective masses) of excited carriers.

Theoretical Probing of Weak Anion-Cation Interactions in Certain Pyridinium-Based Ionic Liquid Ion Pairs and the Application of Molecular Electrostatic Potential in Their Ionic Crystal Density Determination: A Comparative Study Using Density Functional Approach.

Science.gov (United States)

Joseph, Aswathy; Thomas, Vibin Ipe; Żyła, Gaweł; Padmanabhan, A S; Mathew, Suresh

2018-01-11

A comprehensive study on the structure, nature of interaction, and properties of six ionic pairs of 1-butylpyridinium and 1-butyl-4-methylpyridinium cations in combination with tetrafluoroborate (BF 4 - ), chloride (Cl - ), and bromide (Br - ) anions have been carried out using density functional theory (DFT). The anion-cation interaction energy (ΔE int ), thermochemistry values, theoretical band gap, molecular orbital energy order, DFT-based chemical activity descriptors [chemical potential (μ), chemical hardness (η), and electrophilicity index (ω)], and distribution of density of states (DOS) of these ion pairs were investigated. The ascendancy of the -CH 3 substituent at the fourth position of the 1-butylpyridinium cation ring on the values of ΔE int , theoretical band gap and chemical activity descriptors was evaluated. The ΔE int values were negative for all six ion pairs and were highest for Cl - containing ion pairs. The theoretical band gap value after -CH 3 substitution increased from 3.78 to 3.96 eV (for Cl - ) and from 2.74 to 2.88 eV (for Br - ) and decreased from 4.9 to 4.89 eV (for BF 4 - ). Ion pairs of BF 4 - were more susceptible to charge transfer processes as inferred from their significantly high η values and comparatively small difference in ω value after -CH 3 substitution. The change in η and μ values due to the -CH 3 substituent is negligibly small in all cases except for the ion pairs of Cl - . Critical-point (CP) analyses were carried out to investigate the AIM topological parameters at the interionic bond critical points (BCPs). The RDG isosurface analysis indicated that the anion-cation interaction was dominated by strong H cat ···X ani and C cat ···X ani interactions in ion pairs of Cl - and Br - whereas a weak van der Waal's effect dominated in ion pairs of BF 4 - . The molecular electrostatic potential (MESP)-based parameter ΔΔV min measuring the anion-cation interaction strength showed a good linear correlation with

When Density Functional Approximations Meet Iron Oxides.

Science.gov (United States)

Meng, Yu; Liu, Xing-Wu; Huo, Chun-Fang; Guo, Wen-Ping; Cao, Dong-Bo; Peng, Qing; Dearden, Albert; Gonze, Xavier; Yang, Yong; Wang, Jianguo; Jiao, Haijun; Li, Yongwang; Wen, Xiao-Dong

2016-10-11

Three density functional approximations (DFAs), PBE, PBE+U, and Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE), were employed to investigate the geometric, electronic, magnetic, and thermodynamic properties of four iron oxides, namely, α-FeOOH, α-Fe 2 O 3 , Fe 3 O 4 , and FeO. Comparing our calculated results with available experimental data, we found that HSE (a = 0.15) (containing 15% "screened" Hartree-Fock exchange) can provide reliable values of lattice constants, Fe magnetic moments, band gaps, and formation energies of all four iron oxides, while standard HSE (a = 0.25) seriously overestimates the band gaps and formation energies. For PBE+U, a suitable U value can give quite good results for the electronic properties of each iron oxide, but it is challenging to accurately get other properties of the four iron oxides using the same U value. Subsequently, we calculated the Gibbs free energies of transformation reactions among iron oxides using the HSE (a = 0.15) functional and plotted the equilibrium phase diagrams of the iron oxide system under various conditions, which provide reliable theoretical insight into the phase transformations of iron oxides.

Single-particle energies and density of states in density functional theory

Science.gov (United States)

van Aggelen, H.; Chan, G. K.-L.

2015-07-01

Time-dependent density functional theory (TD-DFT) is commonly used as the foundation to obtain neutral excited states and transition weights in DFT, but does not allow direct access to density of states and single-particle energies, i.e. ionisation energies and electron affinities. Here we show that by extending TD-DFT to a superfluid formulation, which involves operators that break particle-number symmetry, we can obtain the density of states and single-particle energies from the poles of an appropriate superfluid response function. The standard Kohn- Sham eigenvalues emerge as the adiabatic limit of the superfluid response under the assumption that the exchange- correlation functional has no dependence on the superfluid density. The Kohn- Sham eigenvalues can thus be interpreted as approximations to the ionisation energies and electron affinities. Beyond this approximation, the formalism provides an incentive for creating a new class of density functionals specifically targeted at accurate single-particle eigenvalues and bandgaps.

Density of states functions for photonic crystals

International Nuclear Information System (INIS)

McPhedran, R.C.; McOrist, J.; Sterke, C.M. de; Nicorovici, N.A.; Botten, L.C.; Asatryan, A.A.

2004-01-01

We discuss density of states functions for photonic crystals, in the context of the two-dimensional problem for arrays of cylinders of arbitrary cross section. We introduce the mutual density of states (MDOS), and show that this function can be used to calculate both the local density of states (LDOS), which gives position information for emission of radiation from photonic crystals, and the spectral density of states (SDOS), which gives angular information. We establish the connection between MDOS, LDOS, SDOS and the conventional density of states, which depends only on frequency. We relate all four functions to the band structure and propagating states within the crystal, and give numerical examples of the relation between band structure and density of states functions

Nonlocal kinetic-energy-density functionals

International Nuclear Information System (INIS)

Garcia-Gonzalez, P.; Alvarellos, J.E.; Chacon, E.

1996-01-01

In this paper we present nonlocal kinetic-energy functionals T[n] within the average density approximation (ADA) framework, which do not require any extra input when applied to any electron system and recover the exact kinetic energy and the linear response function of a homogeneous system. In contrast with previous ADA functionals, these present good behavior of the long-range tail of the exact weight function. The averaging procedure for the kinetic functional (averaging the Fermi momentum of the electron gas, instead of averaging the electron density) leads to a functional without numerical difficulties in the calculation of extended systems, and it gives excellent results when applied to atoms and jellium surfaces. copyright 1996 The American Physical Society

Uncertainty quantification for nuclear density functional theory and information content of new measurements

Energy Technology Data Exchange (ETDEWEB)

McDonnell, J. D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Schunck, N. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Higdon, D. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Sarich, J. [Argonne National Lab. (ANL), Argonne, IL (United States); Wild, S. M. [Argonne National Lab. (ANL), Argonne, IL (United States); Nazarewicz, W. [Michigan State Univ., East Lansing, MI (United States); Oak Ridge National Lab., Oak Ridge, TN (United States); Univ. of Warsaw, Warsaw (Poland)

2015-03-24

Statistical tools of uncertainty quantification can be used to assess the information content of measured observables with respect to present-day theoretical models, to estimate model errors and thereby improve predictive capability, to extrapolate beyond the regions reached by experiment, and to provide meaningful input to applications and planned measurements. To showcase new opportunities offered by such tools, we make a rigorous analysis of theoretical statistical uncertainties in nuclear density functional theory using Bayesian inference methods. By considering the recent mass measurements from the Canadian Penning Trap at Argonne National Laboratory, we demonstrate how the Bayesian analysis and a direct least-squares optimization, combined with high-performance computing, can be used to assess the information content of the new data with respect to a model based on the Skyrme energy density functional approach. Employing the posterior probability distribution computed with a Gaussian process emulator, we apply the Bayesian framework to propagate theoretical statistical uncertainties in predictions of nuclear masses, two-neutron dripline, and fission barriers. Overall, we find that the new mass measurements do not impose a constraint that is strong enough to lead to significant changes in the model parameters. As a result, the example discussed in this study sets the stage for quantifying and maximizing the impact of new measurements with respect to current modeling and guiding future experimental efforts, thus enhancing the experiment-theory cycle in the scientific method.

Collision dynamics of H+ + N2 at low energies based on time-dependent density-functional theory

Science.gov (United States)

Yu, W.; Zhang, Y.; Zhang, F. S.; Hutton, R.; Zou, Y.; Gao, C.-Z.; Wei, B.

2018-02-01

Using time-dependent density-functional theory at the level of local density approximation augmented by a self-interaction correction and coupled non-adiabatically to molecular dynamics, we study, from a theoretical perspective, scattering dynamics of the proton in collisions with the N2 molecule at 30 eV. Nine different collision configurations are employed to analyze the proton energy loss spectra, electron depletion, scattering angles and self-interaction effects. Our results agree qualitatively with the experimental data and previous theoretical calculations. The discrepancies are ascribed to the limitation of the theoretical models in use. We find that self-interaction effects can significantly influence the electron capture and the excited diatomic vibrational motion, which is in consistent with other calculations. In addition, it is found that the molecular structure can be readily retrieved from the proton energy loss spectra due to a significant momentum transfer in head-on collisions.

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

Science.gov (United States)

Tao, Jianmin; Ye, Lin-Hui; Duan, Yuhua

2017-12-01

The primary goal of Kohn-Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao-Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree-Fock density yields the exchange and correlation energies in good agreement with the Optimized Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Finally, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.

A multiconfigurational hybrid density-functional theory

DEFF Research Database (Denmark)

Sharkas, Kamal; Savin, Andreas; Jensen, Hans Jørgen Aagaard

2012-01-01

We propose a multiconfigurational hybrid density-functional theory which rigorously combines a multiconfiguration self-consistent-field calculation with a density-functional approximation based on a linear decomposition of the electron-electron interaction. This gives a straightforward extension ...

Local density approximation for exchange in excited-state density functional theory

OpenAIRE

Harbola, Manoj K.; Samal, Prasanjit

2004-01-01

Local density approximation for the exchange energy is made for treatment of excited-states in density-functional theory. It is shown that taking care of the state-dependence of the LDA exchange energy functional leads to accurate excitation energies.

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.

Dictionary-Based Stochastic Expectation–Maximization for SAR Amplitude Probability Density Function Estimation

OpenAIRE

Moser , Gabriele; Zerubia , Josiane; Serpico , Sebastiano B.

2006-01-01

International audience; In remotely sensed data analysis, a crucial problem is represented by the need to develop accurate models for the statistics of the pixel intensities. This paper deals with the problem of probability density function (pdf) estimation in the context of synthetic aperture radar (SAR) amplitude data analysis. Several theoretical and heuristic models for the pdfs of SAR data have been proposed in the literature, which have been proved to be effective for different land-cov...

Ab initio quasi-particle approximation bandgaps of silicon nanowires calculated at density functional theory/local density approximation computational effort

Energy Technology Data Exchange (ETDEWEB)

Ribeiro, M., E-mail: ribeiro.jr@oorbit.com.br [Office of Operational Research for Business Intelligence and Technology, Principal Office, Buffalo, Wyoming 82834 (United States)

2015-06-21

Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost.

Ab initio quasi-particle approximation bandgaps of silicon nanowires calculated at density functional theory/local density approximation computational effort

International Nuclear Information System (INIS)

Ribeiro, M.

2015-01-01

Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost

Dual descriptors within the framework of spin-polarized density functional theory.

Science.gov (United States)

Chamorro, E; Pérez, P; Duque, M; De Proft, F; Geerlings, P

2008-08-14

Spin-polarized density functional theory (SP-DFT) allows both the analysis of charge-transfer (e.g., electrophilic and nucleophilic reactivity) and of spin-polarization processes (e.g., photophysical changes arising from electron transitions). In analogy with the dual descriptor introduced by Morell et al. [J. Phys. Chem. A 109, 205 (2005)], we introduce new dual descriptors intended to simultaneously give information of the molecular regions where the spin-polarization process linking states of different multiplicity will drive electron density and spin density changes. The electronic charge and spin rearrangement in the spin forbidden radiative transitions S(0)-->T(n,pi(*)) and S(0)-->T(pi,pi(*)) in formaldehyde and ethylene, respectively, have been used as benchmark examples illustrating the usefulness of the new spin-polarization dual descriptors. These quantities indicate those regions where spin-orbit coupling effects are at work in such processes. Additionally, the qualitative relationship between the topology of the spin-polarization dual descriptors and the vertical singlet triplet energy gap in simple substituted carbene series has been also discussed. It is shown that the electron density and spin density rearrangements arise in agreement with spectroscopic experimental evidence and other theoretical results on the selected target systems.

Local elastic properties of nano-confined fluids: A density functional study

Energy Technology Data Exchange (ETDEWEB)

Sun, Zongli, E-mail: zongli_sun@163.com [Science and Technology College, North China Electric Power University, Baoding 071051 (China); Kang, Yanshuang [College of Science, Agriculture University of Hebei, Baoding 071001 (China)

2014-05-01

The understanding of mechanical properties of confined fluids is essential for modeling and manipulating of nano-scaled systems. Unlike the uniform phase, the confined fluids usually display different features in structure and related properties. Due to the presence of the confining geometry, the density profile and many physical and chemical properties may be position-dependent. The aim of our research is to derive an expression for the local elastic property by using the classical elastic theory. Both the bulk and shear moduli are expressed as functional of density of particle. The theoretical result derived is applied to the Lennard-Jones fluids confined in nano-cavity. Comparison of our numerical result and the simulation result is made and qualitative agreement is observed. Further, influence of bulk density, temperature and external potential on moduli is calculated and the physical mechanism is analyzed. Relationship between contact modulus and the interfacial tension is also calculated. Their opposite trend with temperature is observed.

Local elastic properties of nano-confined fluids: A density functional study

International Nuclear Information System (INIS)

Sun, Zongli; Kang, Yanshuang

2014-01-01

The understanding of mechanical properties of confined fluids is essential for modeling and manipulating of nano-scaled systems. Unlike the uniform phase, the confined fluids usually display different features in structure and related properties. Due to the presence of the confining geometry, the density profile and many physical and chemical properties may be position-dependent. The aim of our research is to derive an expression for the local elastic property by using the classical elastic theory. Both the bulk and shear moduli are expressed as functional of density of particle. The theoretical result derived is applied to the Lennard-Jones fluids confined in nano-cavity. Comparison of our numerical result and the simulation result is made and qualitative agreement is observed. Further, influence of bulk density, temperature and external potential on moduli is calculated and the physical mechanism is analyzed. Relationship between contact modulus and the interfacial tension is also calculated. Their opposite trend with temperature is observed.

Comparison of chlorine and oxygen adsorption on the ferromagnetic Fe(0 0 1) surface: Density-functional theory study

Czech Academy of Sciences Publication Activity Database

Pick, Štěpán

2008-01-01

Roč. 602, č. 24 (2008), s. 3733-3736 ISSN 0039-6028 Institutional research plan: CEZ:AV0Z40400503 Keywords : density functional calculation * spin-dependent phenomena * chemisorption Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.731, year: 2008

Locality of correlation in density functional theory

Energy Technology Data Exchange (ETDEWEB)

Burke, Kieron [Department of Chemistry, University of California, Irvine, California 92697 (United States); Cancio, Antonio [Department of Physics and Astronomy, Ball State University, Muncie, Indiana 47306 (United States); Gould, Tim [Qld Micro- and Nanotechnology Centre, Griffith University, Nathan, Qld 4111 (Australia); Pittalis, Stefano [CNR-Istituto di Nanoscienze, Via Campi 213A, I-41125 Modena (Italy)

2016-08-07

The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that E{sub C} → −A{sub C} ZlnZ + B{sub C}Z as Z → ∞, where Z is the atomic number, A{sub C} is known, and we estimate B{sub C} to be about 37 mhartree. The local density approximation yields A{sub C} exactly, but a very incorrect value for B{sub C}, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with B{sub C} a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed.

Fundamentals of time-dependent density functional theory

International Nuclear Information System (INIS)

Marques, Miguel A.L.; Rubio, Angel

2012-01-01

There have been many significant advances in time-dependent density functional theory over recent years, both in enlightening the fundamental theoretical basis of the theory, as well as in computational algorithms and applications. This book, as successor to the highly successful volume Time-Dependent Density Functional Theory (Lect. Notes Phys. 706, 2006) brings together for the first time all recent developments in a systematic and coherent way. First, a thorough pedagogical presentation of the fundamental theory is given, clarifying aspects of the original proofs and theorems, as well as presenting fresh developments that extend the theory into new realms such as alternative proofs of the original Runge-Gross theorem, open quantum systems, and dispersion forces to name but a few. Next, all of the basic concepts are introduced sequentially and building in complexity, eventually reaching the level of open problems of interest. Contemporary applications of the theory are discussed, from real-time coupled-electron-ion dynamics, to excited-state dynamics and molecular transport. Last but not least, the authors introduce and review recent advances in computational implementation, including massively parallel architectures and graphical processing units. Special care has been taken in editing this volume as a multi-author textbook, following a coherent line of thought, and making all the relevant connections between chapters and concepts consistent throughout. As such it will prove to be the text of reference in this field, both for beginners as well as expert researchers and lecturers teaching advanced quantum mechanical methods to model complex physical systems, from molecules to nanostructures, from biocomplexes to surfaces, solids and liquids. (orig.)

Density Functional Theory applied to magnetic materials: Mn{sub 3}O{sub 4} at different hybrid functionals

Energy Technology Data Exchange (ETDEWEB)

Ribeiro, R.A.P. [Department of Chemistry, State University of Ponta Grossa, Av. General Carlos Cavalcanti, 4748, 84030-900 Ponta Grossa, PR (Brazil); Lazaro, S.R. de, E-mail: srlazaro@upeg.br [Department of Chemistry, State University of Ponta Grossa, Av. General Carlos Cavalcanti, 4748, 84030-900 Ponta Grossa, PR (Brazil); Pianaro, S.A. [Department of Materials Engineering, State University of Ponta Grossa, Av. General Carlos Cavalcanti, 4748, 84030-900 Ponta Grossa, PR (Brazil)

2015-10-01

Antiferromagnetic Mn{sub 3}O{sub 4} in spinel structure was investigated employing the Density Functional Theory at different hybrid functionals with default HF exchange percentage. Structural, electronic and magnetic properties were examined. Structural results were in agreement with experimental and Hartree–Fock results showing that the octahedral site was distorted by the Jahn–Teller effect, which changed the electron density distribution. Band-gap results for B3LYP and B3PW hybrid functionals were closer to the experimental when compared to PBE0. Mulliken Population Analysis revealed magnetic moments very close to ideal d{sup 4} and d{sup 5} electron configurations of Mn{sup 3+} and Mn{sup 2+}, respectively. Electron density maps are useful to determine that oxygen atoms mediate the electron transfer between octahedral and tetrahedral clusters. Magnetic properties were investigated from theoretical results for exchange coupling constants. Intratetrahedral and tetra-octahedral interactions were observed to be antiferromagnetic, whereas, octahedral sites presented antiferromagnetic interactions in the same layer and ferromagnetic in adjacent layers. Results showed that only default B3LYP was successful to describe magnetic properties of antiferromagnetic materials in agreement with experimental results. - Highlights: • We study structural, electronic and magnetic properties of antiferromagnetic Mn{sub 3}O{sub 4}. • B3LYP, B3PW and PBE0 hybrid functionals are compared. • B3LYP and B3PW hybrid functionals are better to band-gap calculations. • Only default B3LYP was successful to describe exchange interactions for Mn{sub 3}O{sub 4}.

The Density Functional Theory of Flies: Predicting distributions of interacting active organisms

Science.gov (United States)

Kinkhabwala, Yunus; Valderrama, Juan; Cohen, Itai; Arias, Tomas

On October 2nd, 2016, 52 people were crushed in a stampede when a crowd panicked at a religious gathering in Ethiopia. The ability to predict the state of a crowd and whether it is susceptible to such transitions could help prevent such catastrophes. While current techniques such as agent based models can predict transitions in emergent behaviors of crowds, the assumptions used to describe the agents are often ad hoc and the simulations are computationally expensive making their application to real-time crowd prediction challenging. Here, we pursue an orthogonal approach and ask whether a reduced set of variables, such as the local densities, are sufficient to describe the state of a crowd. Inspired by the theoretical framework of Density Functional Theory, we have developed a system that uses only measurements of local densities to extract two independent crowd behavior functions: (1) preferences for locations and (2) interactions between individuals. With these two functions, we have accurately predicted how a model system of walking Drosophila melanogaster distributes itself in an arbitrary 2D environment. In addition, this density-based approach measures properties of the crowd from only observations of the crowd itself without any knowledge of the detailed interactions and thus it can make predictions about the resulting distributions of these flies in arbitrary environments, in real-time. This research was supported in part by ARO W911NF-16-1-0433.

Density functionals in the laboratory frame

International Nuclear Information System (INIS)

Giraud, B. G.

2008-01-01

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

Building a Universal Nuclear Energy Density Functional

Energy Technology Data Exchange (ETDEWEB)

Carlson, Joe A. [Michigan State Univ., East Lansing, MI (United States); Furnstahl, Dick; Horoi, Mihai; Lust, Rusty; Nazaewicc, Witek; Ng, Esmond; Thompson, Ian; Vary, James

2012-12-30

During the period of Dec. 1 2006 – Jun. 30, 2012, the UNEDF collaboration carried out a comprehensive study of all nuclei, based on the most accurate knowledge of the strong nuclear interaction, the most reliable theoretical approaches, the most advanced algorithms, and extensive computational resources, with a view towards scaling to the petaflop platforms and beyond. The long-term vision initiated with UNEDF is to arrive at a comprehensive, quantitative, and unified description of nuclei and their reactions, grounded in the fundamental interactions between the constituent nucleons. We seek to replace current phenomenological models of nuclear structure and reactions with a well-founded microscopic theory that delivers maximum predictive power with well-quantified uncertainties. Specifically, the mission of this project has been three-fold: First, to find an optimal energy density functional (EDF) using all our knowledge of the nucleonic Hamiltonian and basic nuclear properties; Second, to apply the EDF theory and its extensions to validate the functional using all the available relevant nuclear structure and reaction data; Third, to apply the validated theory to properties of interest that cannot be measured, in particular the properties needed for reaction theory.

A density functional perturbative approach for simple fluids: the structure of a nonuniform Lennard-Jones fluid at interfaces

International Nuclear Information System (INIS)

Kim, Soon-Chul; Lee, Song Hi

2004-01-01

A density functional perturbation approximation (DFPT), which is based both on the fundamental-measure theory (FMT) to the hard-sphere repulsion and on the weighted-density approximations (WDAs) to the attractive contribution, has been proposed for studying the structural properties of model fluids with an attractive part of the potential. The advantage of the present theory is the simplicity of the calculation of the weight function due to the attractive contribution. It has been applied to predict the equilibrium particle density distributions and adsorption isotherms of Lennard-Jones fluids at interfaces. The theoretical results show that the present theory describes quite well the adsorption isotherms of a Lennard-Jones ethane in a graphite slit pore as well as the equilibrium particle density distributions of a Lennard-Jones fluid near a planar slit pore

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.

Explicit polarization (X-Pol) potential using ab initio molecular orbital theory and density functional theory.

Science.gov (United States)

Song, Lingchun; Han, Jaebeom; Lin, Yen-lin; Xie, Wangshen; Gao, Jiali

2009-10-29

The explicit polarization (X-Pol) method has been examined using ab initio molecular orbital theory and density functional theory. The X-Pol potential was designed to provide a novel theoretical framework for developing next-generation force fields for biomolecular simulations. Importantly, the X-Pol potential is a general method, which can be employed with any level of electronic structure theory. The present study illustrates the implementation of the X-Pol method using ab initio Hartree-Fock theory and hybrid density functional theory. The computational results are illustrated by considering a set of bimolecular complexes of small organic molecules and ions with water. The computed interaction energies and hydrogen bond geometries are in good accord with CCSD(T) calculations and B3LYP/aug-cc-pVDZ optimizations.

Perspective: Fifty years of density-functional theory in chemical physics

International Nuclear Information System (INIS)

Becke, Axel D.

2014-01-01

Since its formal inception in 1964–1965, Kohn-Sham density-functional theory (KS-DFT) has become the most popular electronic structure method in computational physics and chemistry. Its popularity stems from its beautifully simple conceptual framework and computational elegance. The rise of KS-DFT in chemical physics began in earnest in the mid 1980s, when crucial developments in its exchange-correlation term gave the theory predictive power competitive with well-developed wave-function methods. Today KS-DFT finds itself under increasing pressure to deliver higher and higher accuracy and to adapt to ever more challenging problems. If we are not mindful, however, these pressures may submerge the theory in the wave-function sea. KS-DFT might be lost. I am hopeful the Kohn-Sham philosophical, theoretical, and computational framework can be preserved. This Perspective outlines the history, basic concepts, and present status of KS-DFT in chemical physics, and offers suggestions for its future development

Perspective: Fifty years of density-functional theory in chemical physics

Energy Technology Data Exchange (ETDEWEB)

Becke, Axel D., E-mail: axel.becke@dal.ca [Department of Chemistry, Dalhousie University, 6274 Coburg Rd., P.O. Box 15000, Halifax, Nova Scotia B3H 4R2 (Canada)

2014-05-14

Since its formal inception in 1964–1965, Kohn-Sham density-functional theory (KS-DFT) has become the most popular electronic structure method in computational physics and chemistry. Its popularity stems from its beautifully simple conceptual framework and computational elegance. The rise of KS-DFT in chemical physics began in earnest in the mid 1980s, when crucial developments in its exchange-correlation term gave the theory predictive power competitive with well-developed wave-function methods. Today KS-DFT finds itself under increasing pressure to deliver higher and higher accuracy and to adapt to ever more challenging problems. If we are not mindful, however, these pressures may submerge the theory in the wave-function sea. KS-DFT might be lost. I am hopeful the Kohn-Sham philosophical, theoretical, and computational framework can be preserved. This Perspective outlines the history, basic concepts, and present status of KS-DFT in chemical physics, and offers suggestions for its future development.

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...

Reduced density matrix functional theory via a wave function based approach

Energy Technology Data Exchange (ETDEWEB)

Schade, Robert; Bloechl, Peter [Institute for Theoretical Physics, Clausthal University of Technology, Clausthal (Germany); Pruschke, Thomas [Institute for Theoretical Physics, University of Goettingen, Goettingen (Germany)

2016-07-01

We propose a new method for the calculation of the electronic and atomic structure of correlated electron systems based on reduced density matrix functional theory (rDMFT). The density-matrix functional is evaluated on the fly using Levy's constrained search formalism. The present implementation rests on a local approximation of the interaction reminiscent to that of dynamical mean field theory (DMFT). We focus here on additional approximations to the exact density-matrix functional in the local approximation and evaluate their performance.

A real-space stochastic density matrix approach for density functional electronic structure.

Science.gov (United States)

Beck, Thomas L

2015-12-21

The recent development of real-space grid methods has led to more efficient, accurate, and adaptable approaches for large-scale electrostatics and density functional electronic structure modeling. With the incorporation of multiscale techniques, linear-scaling real-space solvers are possible for density functional problems if localized orbitals are used to represent the Kohn-Sham energy functional. These methods still suffer from high computational and storage overheads, however, due to extensive matrix operations related to the underlying wave function grid representation. In this paper, an alternative stochastic method is outlined that aims to solve directly for the one-electron density matrix in real space. In order to illustrate aspects of the method, model calculations are performed for simple one-dimensional problems that display some features of the more general problem, such as spatial nodes in the density matrix. This orbital-free approach may prove helpful considering a future involving increasingly parallel computing architectures. Its primary advantage is the near-locality of the random walks, allowing for simultaneous updates of the density matrix in different regions of space partitioned across the processors. In addition, it allows for testing and enforcement of the particle number and idempotency constraints through stabilization of a Feynman-Kac functional integral as opposed to the extensive matrix operations in traditional approaches.

Decay of autoionizing states in time-dependent density functional and reduced density matrix functional theory

Energy Technology Data Exchange (ETDEWEB)

Kapoor, Varun; Brics, Martins; Bauer, Dieter [Institut fuer Physik, Universitaet Rostock, 18051 Rostock (Germany)

2013-07-01

Autoionizing states are inaccessible to time-dependent density functional theory (TDDFT) using known, adiabatic Kohn-Sham (KS) potentials. We determine the exact KS potential for a numerically exactly solvable model Helium atom interacting with a laser field that is populating an autoionizing state. The exact single-particle density of the population in the autoionizing state corresponds to that of the energetically lowest quasi-stationary state in the exact KS potential. We describe how this exact potential controls the decay by a barrier whose height and width allows for the density to tunnel out and decay with the same rate as in the ab initio time-dependent Schroedinger calculation. However, devising a useful exchange-correlation potential that is capable of governing such a scenario in general and in more complex systems is hopeless. As an improvement over TDDFT, time-dependent reduced density matrix functional theory has been proposed. We are able to obtain for the above described autoionization process the exact time-dependent natural orbitals (i.e., the eigenfunctions of the exact, time-dependent one-body reduced density matrix) and study the potentials that appear in the equations of motion for the natural orbitals and the structure of the two-body density matrix expanded in them.

Density Functional Study of Chemical Reaction Equilibrium for Dimerization Reactions in Slit and Cylindrical Nanopores

Czech Academy of Sciences Publication Activity Database

Malijevský, Alexandr; Lísal, Martin

2009-01-01

Roč. 130, č. 16 (2009), 164713-1-24 ISSN 0021-9606 R&D Projects: GA ČR GA203/05/0725; GA AV ČR 1ET400720507; GA AV ČR KAN400720701 Institutional research plan: CEZ:AV0Z40720504 Keywords : density functional theory * reaction ensemble Monte Carlo * reaction equilibrium Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.093, year: 2009

Game theoretic aspect of production process transfer functions ...

African Journals Online (AJOL)

Game theoretic aspect of production process transfer functions. ... On the final analysis, it was shown that relating transfer function to Bayesian games and mechanism design would lead to optimal bids, optimal ... AJOL African Journals Online.

Self-Interaction Error in Density Functional Theory: An Appraisal.

Science.gov (United States)

Bao, Junwei Lucas; Gagliardi, Laura; Truhlar, Donald G

2018-05-03

Self-interaction error (SIE) is considered to be one of the major sources of error in most approximate exchange-correlation functionals for Kohn-Sham density-functional theory (KS-DFT), and it is large with all local exchange-correlation functionals and with some hybrid functionals. In this work, we consider systems conventionally considered to be dominated by SIE. For these systems, we demonstrate that by using multiconfiguration pair-density functional theory (MC-PDFT), the error of a translated local density-functional approximation is significantly reduced (by a factor of 3) when using an MCSCF density and on-top density, as compared to using KS-DFT with the parent functional; the error in MC-PDFT with local on-top functionals is even lower than the error in some popular KS-DFT hybrid functionals. Density-functional theory, either in MC-PDFT form with local on-top functionals or in KS-DFT form with some functionals having 50% or more nonlocal exchange, has smaller errors for SIE-prone systems than does CASSCF, which has no SIE.

Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

International Nuclear Information System (INIS)

Tait, E W; Payne, M C; Ratcliff, L E; Haynes, P D; Hine, N D M

2016-01-01

Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable. (paper)

Density functional theory and parallel processing

International Nuclear Information System (INIS)

Ward, R.C.; Geist, G.A.; Butler, W.H.

1987-01-01

The authors demonstrate a method for obtaining the ground state energies and charge densities of a system of atoms described within density functional theory using simulated annealing on a parallel computer

Quasi-particle energy spectra in local reduced density matrix functional theory.

Science.gov (United States)

Lathiotakis, Nektarios N; Helbig, Nicole; Rubio, Angel; Gidopoulos, Nikitas I

2014-10-28

Recently, we introduced [N. N. Lathiotakis, N. Helbig, A. Rubio, and N. I. Gidopoulos, Phys. Rev. A 90, 032511 (2014)] local reduced density matrix functional theory (local RDMFT), a theoretical scheme capable of incorporating static correlation effects in Kohn-Sham equations. Here, we apply local RDMFT to molecular systems of relatively large size, as a demonstration of its computational efficiency and its accuracy in predicting single-electron properties from the eigenvalue spectrum of the single-particle Hamiltonian with a local effective potential. We present encouraging results on the photoelectron spectrum of molecular systems and the relative stability of C20 isotopes. In addition, we propose a modelling of the fractional occupancies as functions of the orbital energies that further improves the efficiency of the method useful in applications to large systems and solids.

Subsystem density functional theory with meta-generalized gradient approximation exchange-correlation functionals.

Science.gov (United States)

Śmiga, Szymon; Fabiano, Eduardo; Laricchia, Savio; Constantin, Lucian A; Della Sala, Fabio

2015-04-21

We analyze the methodology and the performance of subsystem density functional theory (DFT) with meta-generalized gradient approximation (meta-GGA) exchange-correlation functionals for non-bonded molecular systems. Meta-GGA functionals depend on the Kohn-Sham kinetic energy density (KED), which is not known as an explicit functional of the density. Therefore, they cannot be directly applied in subsystem DFT calculations. We propose a Laplacian-level approximation to the KED which overcomes this limitation and provides a simple and accurate way to apply meta-GGA exchange-correlation functionals in subsystem DFT calculations. The so obtained density and energy errors, with respect to the corresponding supermolecular calculations, are comparable with conventional approaches, depending almost exclusively on the approximations in the non-additive kinetic embedding term. An embedding energy error decomposition explains the accuracy of our method.

Level Densities and Radiative Strength Functions in ⁵⁶FE and ⁵⁷FE

Energy Technology Data Exchange (ETDEWEB)

Tavukcu, Emel [North Carolina State Univ., Raleigh, NC (United States)

2002-12-10

Understanding nuclear level densities and radiative strength functions is important for pure and applied nuclear physics. Recently, the Oslo Cyclotron Group has developed an experimental method to extract level densities and radiative strength functions simultaneously from the primary γ rays after a light-ion reaction. A primary γ-ray spectrum represents the γ-decay probability distribution. The Oslo method is based on the Axel-Brink hypothesis, according to which the primary γ-ray spectrum is proportional to the product of the level density at the final energy and the radiative strength function. The level density and the radiative strength function are fit to the experimental primary γ-ray spectra, and then normalized to known data. The method works well for heavy nuclei. The present measurements extend the Oslo method to the lighter mass nuclei ⁵⁶Fe and ⁵⁷Fe. The experimental level densities in ⁵⁶Fe and ⁵⁷Fe reveal step structure. This step structure is a signature for nucleon pair breaking. The predicted pairing gap parameter is in good agreement with the step corresponding to the first pair breaking. Thermodynamic quantities for ⁵⁶Fe and ⁵⁷Fe are derived within the microcanonical and canonical ensembles using the experimental level densities. Energy-temperature relations are considered using caloric curves and probability density functions. The differences between the thermodynamics of small and large systems are emphasized. The experimental heat capacities are compared with the recent theoretical calculations obtained in the Shell Model Monte Carlo method. Radiative strength functions in ⁵⁶Fe and ⁵⁷Fe have surprisingly high values at low γ-ray energies. This behavior has not been observed for heavy nuclei, but has been observed in other light- and medium-mass nuclei. The origin of this low γ-ray energy effect remains unknown.

Building A Universal Nuclear Energy Density Functional (UNEDF)

Energy Technology Data Exchange (ETDEWEB)

Carlson, Joe [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Furnstahl, Dick [The Ohio State Univ., Columbus, OH (United States); Horoi, Mihai [Central Michigan Univ., Mount Pleasant, MI (United States); Lusk, Rusty [Argonne National Lab. (ANL), Argonne, IL (United States); Nazarewicz, Witek [Univ. of Tennessee, Knoxville, TN (United States); Ng, Esmond [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Thompson, Ian [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Vary, James [Iowa State Univ., Ames, IA (United States)

2012-09-30

During the period of Dec. 1 2006 - Jun. 30, 2012, the UNEDF collaboration carried out a comprehensive study of all nuclei, based on the most accurate knowledge of the strong nuclear interaction, the most reliable theoretical approaches, the most advanced algorithms, and extensive computational resources, with a view towards scaling to the petaflop platforms and beyond. The long-term vision initiated with UNEDF is to arrive at a comprehensive, quantitative, and unified description of nuclei and their reactions, grounded in the fundamental interactions between the constituent nucleons. We seek to replace current phenomenological models of nuclear structure and reactions with a well-founded microscopic theory that delivers maximum predictive power with well-quantified uncertainties. Specifically, the mission of this project has been three-fold: first, to find an optimal energy density functional (EDF) using all our knowledge of the nucleonic Hamiltonian and basic nuclear properties; second, to apply the EDF theory and its extensions to validate the functional using all the available relevant nuclear structure and reaction data; third, to apply the validated theory to properties of interest that cannot be measured, in particular the properties needed for reaction theory. The main physics areas of UNEDF, defined at the beginning of the project, were: ab initio structure; ab initio functionals; DFT applications; DFT extensions; reactions.

Oenin and Quercetin Copigmentation: Highlights From Density Functional Theory

Directory of Open Access Journals (Sweden)

Yunkui Li

2018-06-01

Full Text Available Making use of anthocyanin copigmentation, it is possible to effectively improve color quality and stability of red wines and other foods. This can be done by selecting strong copigments, but a 1-fold experimental screening usually entails a high cost and a low efficiency. The aim of this work is to show how a theoretical model based on density functional theory can be useful for an accurate and rapid prediction of copigmentation ability of a copigment. The present study, concerning the copigmentation between oenin and quercetin under the framework of implicit solvent, indicates that, in these conditions, the intermolecular hydrogen bonds play an important role in the system stabilization. The dispersion interaction slightly affects the structure, energies and UV-Vis spectral properties of the copigmentation complex.

Density Functional Theory for Phase-Ordering Transitions

Energy Technology Data Exchange (ETDEWEB)

Wu, Jianzhong [Univ. of California, Riverside, CA (United States)

2016-03-30

Colloids display astonishing structural and dynamic properties that can be dramatically altered by modest changes in the solution condition or an external field. This complex behavior stems from a subtle balance of colloidal forces and intriguing mesoscopic and macroscopic phase transitions that are sensitive to the processing conditions and the dispersing environment. Whereas the knowledge on the microscopic structure and phase behavior of colloidal systems at equilibrium is now well-advanced, quantitative predictions of the dynamic properties and the kinetics of phase-ordering transitions in colloids are not always realized. Many important mesoscopic and off-equilibrium colloidal states remain poorly understood. The proposed research aims to develop a new, unifying approach to describe colloidal dynamics and the kinetics of phase-ordering transitions based on accomplishments from previous work for the equilibrium properties of both uniform and inhomogeneous systems and on novel concepts from the state-of-the-art dynamic density functional theory. In addition to theoretical developments, computational research is designed to address a number of fundamental questions on phase-ordering transitions in colloids, in particular those pertinent to a competition of the dynamic pathways leading to various mesoscopic structures, off-equilibrium states, and crystalline phases. By providing a generic theoretical framework to describe equilibrium, metastable as well as non-ergodic phase transitions concurrent with the colloidal self-assembly processes, accomplishments from this work will have major impacts on both fundamental research and technological applications.

Electronic Structures of Strained InAs x P1-x by Density Functional Theory.

Science.gov (United States)

Lee, Seung Mi; Kim, Min-Young; Kim, Young Heon

2018-09-01

We investigated the effects of strain on the electronic structures of InAsxP1-x using quantum mechanical density functional theory calculations. The electronic band gap and electron effective mass decreased with the increase of the uniaxial tensile strain along the [0001] direction of wurtzite InAs0.75P0.25. Therefore, faster electron movements are expected. These theoretical results are in good agreement with the experimental measurements of InAs0.75P0.25 nanowire.

density functional theory approach

Indian Academy of Sciences (India)

YOGESH ERANDE

2017-07-27

Jul 27, 2017 ... a key role in all optical switching devices, since their optical properties can be .... optimized in the gas phase using Density Functional Theory. (DFT).39 The ...... The Mediation of Electrostatic Effects by Sol- vents J. Am. Chem.

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

Strong Correlation in Kohn-Sham Density Functional Theory

NARCIS (Netherlands)

Malet, F.; Gori Giorgi, P.

2012-01-01

We use the exact strong-interaction limit of the Hohenberg-Kohn energy density functional to approximate the exchange-correlation energy of the restricted Kohn-Sham scheme. Our approximation corresponds to a highly nonlocal density functional whose functional derivative can be easily constructed,

Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

Science.gov (United States)

Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

2015-08-11

The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

Energy–density functional plus quasiparticle–phonon model theory as a powerful tool for nuclear structure and astrophysics

Energy Technology Data Exchange (ETDEWEB)

Tsoneva, N., E-mail: Nadia.Tsoneva@theo.physik.uni-giessen.de [Frankfurt Institute for Advanced Studies (FIAS) (Germany); Lenske, H. [Universität Gießen, Institut für Theoretische Physik (Germany)

2016-11-15

During the last decade, a theoretical method based on the energy–density functional theory and quasiparticle–phonon model, including up to three-phonon configurations was developed. The main advantages of themethod are that it incorporates a self-consistentmean-field and multi-configuration mixing which are found of crucial importance for systematic investigations of nuclear low-energy excitations, pygmy and giant resonances in an unified way. In particular, the theoretical approach has been proven to be very successful in predictions of new modes of excitations, namely pygmy quadrupole resonance which is also lately experimentally observed. Recently, our microscopically obtained dipole strength functions are implemented in predictions of nucleon-capture reaction rates of astrophysical importance. A comparison to available experimental data is discussed.

Functional renormalization group and Kohn-Sham scheme in density functional theory

Science.gov (United States)

Liang, Haozhao; Niu, Yifei; Hatsuda, Tetsuo

2018-04-01

Deriving accurate energy density functional is one of the central problems in condensed matter physics, nuclear physics, and quantum chemistry. We propose a novel method to deduce the energy density functional by combining the idea of the functional renormalization group and the Kohn-Sham scheme in density functional theory. The key idea is to solve the renormalization group flow for the effective action decomposed into the mean-field part and the correlation part. Also, we propose a simple practical method to quantify the uncertainty associated with the truncation of the correlation part. By taking the φ4 theory in zero dimension as a benchmark, we demonstrate that our method shows extremely fast convergence to the exact result even for the highly strong coupling regime.

Linear scaling of density functional algorithms

International Nuclear Information System (INIS)

Stechel, E.B.; Feibelman, P.J.; Williams, A.R.

1993-01-01

An efficient density functional algorithm (DFA) that scales linearly with system size will revolutionize electronic structure calculations. Density functional calculations are reliable and accurate in determining many condensed matter and molecular ground-state properties. However, because current DFA's, including methods related to that of Car and Parrinello, scale with the cube of the system size, density functional studies are not routinely applied to large systems. Linear scaling is achieved by constructing functions that are both localized and fully occupied, thereby eliminating the need to calculate global eigenfunctions. It is, however, widely believed that exponential localization requires the existence of an energy gap between the occupied and unoccupied states. Despite this, the authors demonstrate that linear scaling can still be achieved for metals. Using a linear scaling algorithm, they have explicitly constructed localized, almost fully occupied orbitals for the quintessential metallic system, jellium. The algorithm is readily generalizable to any system geometry and Hamiltonian. They will discuss the conceptual issues involved, convergence properties and scaling for their new algorithm

Density-Functional formalism

International Nuclear Information System (INIS)

Szasz, L.; Berrios-Pagan, I.; McGinn, G.

1975-01-01

A new Density-Functional formula is constructed for atoms. The kinetic energy of the electron is divided into two parts: the kinetic self-energy and the orthogonalization energy. Calculations were made for the total energies of neutral atoms, positive ions and for the He isoelectronic series. For neutral atoms the results match the Hartree-Fock energies within 1% for atoms with N 36 the results generally match the HF energies within 0.1%. For positive ions the results are fair; for the molecular applications a simplified model is developed in which the kinetic energy consists of the Weizsaecker term plus the Fermi energy reduced by a continuous function. (orig.) [de

The force distribution probability function for simple fluids by density functional theory.

Science.gov (United States)

Rickayzen, G; Heyes, D M

2013-02-28

Classical density functional theory (DFT) is used to derive a formula for the probability density distribution function, P(F), and probability distribution function, W(F), for simple fluids, where F is the net force on a particle. The final formula for P(F) ∝ exp(-AF(2)), where A depends on the fluid density, the temperature, and the Fourier transform of the pair potential. The form of the DFT theory used is only applicable to bounded potential fluids. When combined with the hypernetted chain closure of the Ornstein-Zernike equation, the DFT theory for W(F) agrees with molecular dynamics computer simulations for the Gaussian and bounded soft sphere at high density. The Gaussian form for P(F) is still accurate at lower densities (but not too low density) for the two potentials, but with a smaller value for the constant, A, than that predicted by the DFT theory.

Theoretical studies on the electronic structures and spectral properties of a series of bis-cyclometalated iridium(III) complexes using density functional theory

Energy Technology Data Exchange (ETDEWEB)

Han, Deming [International Joint Research Center for Nanophotonics and Biophotonics, School of Life Science and Technology, Changchun University of Science and Technology, Changchun 130022 (China); Zhang, Gang [State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023 (China); Cai, Hongxing; Zhang, Xihe [International Joint Research Center for Nanophotonics and Biophotonics, School of Science, Changchun University of Science and Technology, Changchun 130022 (China); Zhao, Lihui, E-mail: zhaolihui@yahoo.com [International Joint Research Center for Nanophotonics and Biophotonics, School of Life Science and Technology, Changchun University of Science and Technology, Changchun 130022 (China)

2013-06-15

We report a quantum-chemistry study of electronic structures and spectral properties of four Ir(III) complexes Ir[2-(2,4-di-X-phenyl)pyridine]{sub 2}(picolinate), where X=–CH{sub 3} (1), –H (2), –CN (3), –NO{sub 2} (4). The absorption and emission spectra were calculated based on the optimized ground state and excited state geometries, respectively, by means of the time-dependent density functional theory (TDDFT). The effect from the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption, and phosphorescent properties has been investigated. The absorption and emission properties can be altered by the different electron-withdrawing and electron-donating groups. Besides, ionization potential (IP), electron affinities (EA) and reorganization energy (λ{sub hole/electron}) were obtained to evaluate the charge transfer and balance properties between hole and electron. The calculated results show that the different substitute groups affect the charge transfer rate and balance. It can be anticipated that the complexes 3 and 4 have good charge transport rates and balance between the hole and electron. -- Highlights: ► Four Ir(III) complexes have been theoretically investigated. ► The different substituents affect the charge transfer rate and balance. ► We design two candidate materials for OLEDs.

Theoretical studies on the electronic structures and spectral properties of a series of bis-cyclometalated iridium(III) complexes using density functional theory

International Nuclear Information System (INIS)

Han, Deming; Zhang, Gang; Cai, Hongxing; Zhang, Xihe; Zhao, Lihui

2013-01-01

We report a quantum-chemistry study of electronic structures and spectral properties of four Ir(III) complexes Ir[2-(2,4-di-X-phenyl)pyridine] 2 (picolinate), where X=–CH 3 (1), –H (2), –CN (3), –NO 2 (4). The absorption and emission spectra were calculated based on the optimized ground state and excited state geometries, respectively, by means of the time-dependent density functional theory (TDDFT). The effect from the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption, and phosphorescent properties has been investigated. The absorption and emission properties can be altered by the different electron-withdrawing and electron-donating groups. Besides, ionization potential (IP), electron affinities (EA) and reorganization energy (λ hole/electron ) were obtained to evaluate the charge transfer and balance properties between hole and electron. The calculated results show that the different substitute groups affect the charge transfer rate and balance. It can be anticipated that the complexes 3 and 4 have good charge transport rates and balance between the hole and electron. -- Highlights: ► Four Ir(III) complexes have been theoretically investigated. ► The different substituents affect the charge transfer rate and balance. ► We design two candidate materials for OLEDs

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...

The valence and Rydberg states of difluoromethane: A combined experimental vacuum ultraviolet spectrum absorption and theoretical study by ab initio configuration interaction and density functional computations

Science.gov (United States)

Palmer, Michael H.; Vrønning Hoffmann, Søren; Jones, Nykola C.; Coreno, Marcello; de Simone, Monica; Grazioli, Cesare

2018-06-01

The vacuum ultraviolet (VUV) spectrum for CH2F2 from a new synchrotron study has been combined with earlier data and subjected to detailed scrutiny. The onset of absorption, band I and also band IV, is resolved into broad vibrational peaks, which contrast with the continuous absorption previously claimed. A new theoretical analysis, using a combination of time dependent density functional theory (TDDFT) calculations and complete active space self-consistent field, leads to a major new interpretation. Adiabatic excitation energies (AEEs) and vertical excitation energies, evaluated by these methods, are used to interpret the spectra in unprecedented detail using theoretical vibronic analysis. This includes both Franck-Condon (FC) and Herzberg-Teller (HT) effects on cold and hot bands. These results lead to the re-assignment of several known excited states and the identification of new ones. The lowest calculated AEE sequence for singlet states is 11B1 ˜ 11A2 expected; the onset of the 15.5 eV band shows a set of vibrational peaks, but the vibration frequency does not correspond to any of the photoelectron spectral (PES) structure and is clearly valence in nature. The routine use of PES footprints to detect Rydberg states in VUV spectra is shown to be inadequate. The combined effects of FC and HT in the VUV spectral bands lead to additional vibrations when compared with the PES.

Local and linear chemical reactivity response functions at finite temperature in density functional theory

International Nuclear Information System (INIS)

Franco-Pérez, Marco; Ayers, Paul W.; Gázquez, José L.; Vela, Alberto

2015-01-01

We explore the local and nonlocal response functions of the grand canonical potential density functional at nonzero temperature. In analogy to the zero-temperature treatment, local (e.g., the average electron density and the local softness) and nonlocal (e.g., the softness kernel) intrinsic response functions are defined as partial derivatives of the grand canonical potential with respect to its thermodynamic variables (i.e., the chemical potential of the electron reservoir and the external potential generated by the atomic nuclei). To define the local and nonlocal response functions of the electron density (e.g., the Fukui function, the linear density response function, and the dual descriptor), we differentiate with respect to the average electron number and the external potential. The well-known mathematical relationships between the intrinsic response functions and the electron-density responses are generalized to nonzero temperature, and we prove that in the zero-temperature limit, our results recover well-known identities from the density functional theory of chemical reactivity. Specific working equations and numerical results are provided for the 3-state ensemble model

A theoretical model on surface electronic behavior: Strain effect

International Nuclear Information System (INIS)

Qin, W.G.; Shaw, D.

2009-01-01

Deformation from mechanical loading can affect surface electronic behavior. Surface deformation and electronic behavior can be quantitatively expressed using strain and work function, respectively, and their experimental relationship can be readily determined using the Kelvin probing technique. However, the theoretical correlation between work function and strain has been unclear. This study reports our theoretical exploration, for the first time, of the effect of strain on work function. We propose a simple electrostatic action model by considering the effect of a dislocation on work function of a one-dimensional lattice and further extend this model to the complex conditions for the effect of dislocation density. Based on this model, we established successfully a theoretical correlation between work function and strain.

Self-consistent DFT +U method for real-space time-dependent density functional theory calculations

Science.gov (United States)

Tancogne-Dejean, Nicolas; Oliveira, Micael J. T.; Rubio, Angel

2017-12-01

We implemented various DFT+U schemes, including the Agapito, Curtarolo, and Buongiorno Nardelli functional (ACBN0) self-consistent density-functional version of the DFT +U method [Phys. Rev. X 5, 011006 (2015), 10.1103/PhysRevX.5.011006] within the massively parallel real-space time-dependent density functional theory (TDDFT) code octopus. We further extended the method to the case of the calculation of response functions with real-time TDDFT+U and to the description of noncollinear spin systems. The implementation is tested by investigating the ground-state and optical properties of various transition-metal oxides, bulk topological insulators, and molecules. Our results are found to be in good agreement with previously published results for both the electronic band structure and structural properties. The self-consistent calculated values of U and J are also in good agreement with the values commonly used in the literature. We found that the time-dependent extension of the self-consistent DFT+U method yields improved optical properties when compared to the empirical TDDFT+U scheme. This work thus opens a different theoretical framework to address the nonequilibrium properties of correlated systems.

A Safari Through Density Functional Theory

Science.gov (United States)

Dreizler, Reiner M.; Lüdde, Cora S.

Density functional theory is widely used to treat quantum many body problems in many areas of physics and related fields. A brief survey of this method covering foundations, functionals and applications is presented here.

Optical excitation and electron relaxation dynamics at semiconductor surfaces: a combined approach of density functional and density matrix theory applied to the silicon (001) surface

Energy Technology Data Exchange (ETDEWEB)

Buecking, N

2007-11-05

In this work a new theoretical formalism is introduced in order to simulate the phononinduced relaxation of a non-equilibrium distribution to equilibrium at a semiconductor surface numerically. The non-equilibrium distribution is effected by an optical excitation. The approach in this thesis is to link two conventional, but approved methods to a new, more global description: while semiconductor surfaces can be investigated accurately by density-functional theory, the dynamical processes in semiconductor heterostructures are successfully described by density matrix theory. In this work, the parameters for density-matrix theory are determined from the results of density-functional calculations. This work is organized in two parts. In Part I, the general fundamentals of the theory are elaborated, covering the fundamentals of canonical quantizations as well as the theory of density-functional and density-matrix theory in 2{sup nd} order Born approximation. While the formalism of density functional theory for structure investigation has been established for a long time and many different codes exist, the requirements for density matrix formalism concerning the geometry and the number of implemented bands exceed the usual possibilities of the existing code in this field. A special attention is therefore attributed to the development of extensions to existing formulations of this theory, where geometrical and fundamental symmetries of the structure and the equations are used. In Part II, the newly developed formalism is applied to a silicon (001)surface in a 2 x 1 reconstruction. As first step, density-functional calculations using the LDA functional are completed, from which the Kohn-Sham-wave functions and eigenvalues are used to calculate interaction matrix elements for the electron-phonon-coupling an the optical excitation. These matrix elements are determined for the optical transitions from valence to conduction bands and for electron-phonon processes inside the

Comparison of exact-exchange calculations for solids in current-spin-density- and spin-density-functional theory

DEFF Research Database (Denmark)

Sharma, S.; Pittalis, S.; Kurth, S.

2007-01-01

The relative merits of current-spin-density- and spin-density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co......, and Ni) and nonmagnetic (Si and Ge) solids, the exact-exchange current-spin-density functional approach does not significantly improve the accuracy of the corresponding spin-density functional results....

Dynamical density functional theory for dense atomic liquids

International Nuclear Information System (INIS)

Archer, A J

2006-01-01

Starting from Newton's equations of motion, we derive a dynamical density functional theory (DDFT) applicable to atomic liquids. The theory has the feature that it requires as input the Helmholtz free energy functional from equilibrium density functional theory. This means that, given a reliable equilibrium free energy functional, the correct equilibrium fluid density profile is guaranteed. We show that when the isothermal compressibility is small, the DDFT generates the correct value for the speed of sound in a dense liquid. We also interpret the theory as a dynamical equation for a coarse grained fluid density and show that the theory can be used (making further approximations) to derive the standard mode coupling theory that is used to describe the glass transition. The present theory should provide a useful starting point for describing the dynamics of inhomogeneous atomic fluids

Exact free oscillation spectra, splitting functions and the resolvability of Earth's density structure

Science.gov (United States)

Akbarashrafi, F.; Al-Attar, D.; Deuss, A.; Trampert, J.; Valentine, A. P.

2018-04-01

Seismic free oscillations, or normal modes, provide a convenient tool to calculate low-frequency seismograms in heterogeneous Earth models. A procedure called `full mode coupling' allows the seismic response of the Earth to be computed. However, in order to be theoretically exact, such calculations must involve an infinite set of modes. In practice, only a finite subset of modes can be used, introducing an error into the seismograms. By systematically increasing the number of modes beyond the highest frequency of interest in the seismograms, we investigate the convergence of full-coupling calculations. As a rule-of-thumb, it is necessary to couple modes 1-2 mHz above the highest frequency of interest, although results depend upon the details of the Earth model. This is significantly higher than has previously been assumed. Observations of free oscillations also provide important constraints on the heterogeneous structure of the Earth. Historically, this inference problem has been addressed by the measurement and interpretation of splitting functions. These can be seen as secondary data extracted from low frequency seismograms. The measurement step necessitates the calculation of synthetic seismograms, but current implementations rely on approximations referred to as self- or group-coupling and do not use fully accurate seismograms. We therefore also investigate whether a systematic error might be present in currently published splitting functions. We find no evidence for any systematic bias, but published uncertainties must be doubled to properly account for the errors due to theoretical omissions and regularization in the measurement process. Correspondingly, uncertainties in results derived from splitting functions must also be increased. As is well known, density has only a weak signal in low-frequency seismograms. Our results suggest this signal is of similar scale to the true uncertainties associated with currently published splitting functions. Thus, it seems

Vibrational properties of SrCu{sub 2}O{sub 2} studied via Density Functional Theory calculations and compared to Raman and infrared spectroscopy measurements

Energy Technology Data Exchange (ETDEWEB)

Even, J., E-mail: jacky.even@insa.rennes.fr [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); Pedesseau, L.; Durand, O. [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); Modreanu, M. [Tyndall National Institute, Lee Maltings, Prospect Row, Cork (Ireland); Huyberechts, G. [FLAMAC, Technologiepark 903, 9052 Zwijnaarde (Belgium); Servet, B. [Thales Research and Technology France, Campus Polytechnique, 1, avenue Augustin Fresnel, 91767 Palaiseau cedex France (France); Chaix-Pluchery, O. [Laboratoire des Matériaux et du Génie Physique, Grenoble INP—Minatec, 3, parvis Louis Néel, BP 257, 38016 Grenoble Cedex 1 (France)

2013-08-31

The SrCu{sub 2}O{sub 2} material is a p-type transparent conductive oxide. A theoretical study of the SrCu{sub 2}O{sub 2} crystal is performed with a state of the art implementation of the Density Functional Theory. The simulated crystal structure is compared with available X-ray diffraction data and previous theoretical modeling. Density Functional Perturbation Theory is used to study the vibrational properties of the SrCu{sub 2}O{sub 2} crystal. A symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. The Raman spectra simulated using the derivatives of the dielectric susceptibility, show a good agreement with Raman scattering experimental results. - Highlights: ► The symmetry properties of the optical phonons of the SrCu{sub 2}O{sub 2} crystal are analyzed. ► Born charges and the dynamical matrix are calculated at the Brillouin zone center. ► Density Functional Perturbation Theory (DFPT) is used to compute Raman spectrum. ► DFPT Raman spectrum is compared with experimental results.

Constructive definition of functional derivatives in density-functional theory

International Nuclear Information System (INIS)

Luo Ji

2006-01-01

It is shown that the functional derivatives in density-functional theory (DFT) can be explicitly defined within the domain of electron densities restricted by the electron number, and a constructive definition of such restricted derivatives is suggested. With this definition, Kohn-Sham (KS) equations can be established for an N-electron system without extending the functional domain and introducing a Lagrange multiplier. This may clarify some of the fundamental questions raised by Nesbet (1998 Phys. Rev. A 58 R12). The definition naturally leads to the fact that the KS effective potential is determined only to within an additive constant, thus the KS levels can shift freely and the relation between the highest occupied molecular orbital (HOMO) energy and the ionization potential of the system depends on the choice of the constant. On the other hand, if the domain of functionals is indeed extended beyond the electron number restriction, conclusions depend on whether the extended functionals have unrestricted derivatives or not. It is shown that the ensemble extension of DFT to open systems of mixed states (Perdew et al 1982 Phys. Rev. Lett. 49 1691) leads to an energy functional which has no unrestricted derivative at integer electron numbers. Hence after this extension, the relation between the HOMO energy and the ionization potential for an N-electron system is still uncertain. Besides, there are different extensions of the energy functional to a domain of densities unrestricted by the integer electron number, resulting in different unrestricted derivatives and electron systems with different chemical potentials. Even for the exact exchange-correlation potential, there is still an undetermined constant, whether it is a restricted or unrestricted derivative

Density functional theory in quantum chemistry

CERN Document Server

Tsuneda, Takao

2014-01-01

This book examines density functional theory based on the foundation of quantum chemistry. Unconventional in approach, it reviews basic concepts, then describes the physical meanings of state-of-the-art exchange-correlation functionals and their corrections.

Density functional theory for adsorption of gas mixtures in metal-organic frameworks.

Science.gov (United States)

Liu, Yu; Liu, Honglai; Hu, Ying; Jiang, Jianwen

2010-03-04

In this work, a recently developed density functional theory in three-dimensional space was extended to the adsorption of gas mixtures. Weighted density approximations to the excess free energy with different weighting functions were adopted for both repulsive and attractive contributions. An equation of state for hard-sphere mixtures and a modified Benedict-Webb-Rubin equation for Lennard-Jones mixtures were used to estimate the excess free energy of a uniform fluid. The theory was applied to the adsorption of CO(2)/CH(4) and CO(2)/N(2) mixtures in two metal-organic frameworks: ZIF-8 and Zn(2)(BDC)(2)(ted). To validate the theoretical predictions, grand canonical Monte Carlo simulations were also conducted. The predicted adsorption and selectivity from DFT were found to agree well with the simulation results. CO(2) has stronger adsorption than CH(4) and N(2), particularly in Zn(2)(BDC)(2)(ted). The selectivity of CO(2) over CH(4) or N(2) increases with increasing pressure as attributed to the cooperative interactions of adsorbed CO(2) molecules. The composition of the gas mixture exhibits a significant effect on adsorption but not on selectivity.

Comment on 'Kinetic energy as a density functional'

International Nuclear Information System (INIS)

Holas, A.; March, N.H.

2002-01-01

In a recent paper, Nesbet [Phys. Rev. A 65, 010502(R) (2001)] has proposed dropping ''the widespread but unjustified assumption that the existence of a ground-state density functional for the kinetic energy, T s [ρ], of an N-electron system implies the existence of a density-functional derivative, δT s [ρ]/δρ(r), equivalent to a local potential function,'' because, according to his arguments, this derivative 'has the mathematical character of a linear operator that acts on orbital wave functions'. Our Comment demonstrates that the statement called by Nesbet an 'unjustified assumption' happens, in fact, to be a rigorously proven theorem. Therefore, his previous conclusions stemming from his different view of this derivative, which undermined the foundations of density-functional theory, can be discounted

SYNTHESIS, CHARACTERIZATION AND DENSITY FUNCTIONAL ...

African Journals Online (AJOL)

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We synthesized a number of aniline derivatives containing acyl groups to compare their barriers of rotation around ... KEY WORDS: Monoacyl aniline, Synthesis, Density functional theory, Rotation barrier. INTRODUCTION. Developments in ...

Density functional approach to the many-body problem : Key concepts and exact functionals

NARCIS (Netherlands)

van Leeuwen, Robert

2003-01-01

We give an overview of the fundamental concepts of density functional theory. We give a careful discussion of the several density functionals and their differentiability properties. We show that for nondegenerate ground states we can calculate the necessary functional derivatives by means of linear

Consistent Atomic Geometries and Electronic Structure of Five Phases of Potassium Niobate from Density-Functional Theory

Directory of Open Access Journals (Sweden)

Falko Schmidt

2017-01-01

Full Text Available We perform a comprehensive theoretical study of the structural and electronic properties of potassium niobate (KNbO3 in the cubic, tetragonal, orthorhombic, monoclinic, and rhombohedral phase, based on density-functional theory. The influence of different parametrizations of the exchange-correlation functional on the investigated properties is analyzed in detail, and the results are compared to available experimental data. We argue that the PBEsol and AM05 generalized gradient approximations as well as the RTPSS meta-generalized gradient approximation yield consistently accurate structural data for both the external and internal degrees of freedom and are overall superior to the local-density approximation or other conventional generalized gradient approximations for the structural characterization of KNbO3. Band-structure calculations using a HSE-type hybrid functional further indicate significant near degeneracies of band-edge states in all phases which are expected to be relevant for the optical response of the material.

Extended screened exchange functional derived from transcorrelated density functional theory.

Science.gov (United States)

Umezawa, Naoto

2017-09-14

We propose a new formulation of the correlation energy functional derived from the transcorrelated method in use in density functional theory (TC-DFT). An effective Hamiltonian, H TC , is introduced by a similarity transformation of a many-body Hamiltonian, H, with respect to a complex function F: H TC =1FHF. It is proved that an expectation value of H TC for a normalized single Slater determinant, D n , corresponds to the total energy: E[n] = ⟨Ψ n |H|Ψ n ⟩/⟨Ψ n |Ψ n ⟩ = ⟨D n |H TC |D n ⟩ under the two assumptions: (1) The electron density nr associated with a trial wave function Ψ n = D n F is v-representable and (2) Ψ n and D n give rise to the same electron density nr. This formulation, therefore, provides an alternative expression of the total energy that is useful for the development of novel correlation energy functionals. By substituting a specific function for F, we successfully derived a model correlation energy functional, which resembles the functional form of the screened exchange method. The proposed functional, named the extended screened exchange (ESX) functional, is described within two-body integrals and is parametrized for a numerically exact correlation energy of the homogeneous electron gas. The ESX functional does not contain any ingredients of (semi-)local functionals and thus is totally free from self-interactions. The computational cost for solving the self-consistent-field equation is comparable to that of the Hartree-Fock method. We apply the ESX functional to electronic structure calculations for a solid silicon, H - ion, and small atoms. The results demonstrate that the TC-DFT formulation is promising for the systematic improvement of the correlation energy functional.

Theoretical analysis of polarized structure functions

International Nuclear Information System (INIS)

Altarelli, G.; ); Ball, R.D.; Forte, S.; Ridolfi, G.

1998-01-01

We review the analysis of polarized structure function data using perturbative QCD and NLO We use the most recent experimental data to obtain updated results for polarized parton distributions, first moments and the strong coupling. We also discuss several theoretical issues involving in this analysis and in the interpretation of its results. Finally, we compare our results with other similar analyses in the recent literature. (author)

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)

Optimal Bandwidth Selection for Kernel Density Functionals Estimation

Directory of Open Access Journals (Sweden)

Su Chen

2015-01-01

Full Text Available The choice of bandwidth is crucial to the kernel density estimation (KDE and kernel based regression. Various bandwidth selection methods for KDE and local least square regression have been developed in the past decade. It has been known that scale and location parameters are proportional to density functionals ∫γ(xf2(xdx with appropriate choice of γ(x and furthermore equality of scale and location tests can be transformed to comparisons of the density functionals among populations. ∫γ(xf2(xdx can be estimated nonparametrically via kernel density functionals estimation (KDFE. However, the optimal bandwidth selection for KDFE of ∫γ(xf2(xdx has not been examined. We propose a method to select the optimal bandwidth for the KDFE. The idea underlying this method is to search for the optimal bandwidth by minimizing the mean square error (MSE of the KDFE. Two main practical bandwidth selection techniques for the KDFE of ∫γ(xf2(xdx are provided: Normal scale bandwidth selection (namely, “Rule of Thumb” and direct plug-in bandwidth selection. Simulation studies display that our proposed bandwidth selection methods are superior to existing density estimation bandwidth selection methods in estimating density functionals.

Current Density Functional Theory Using Meta-Generalized Gradient Exchange-Correlation Functionals.

Science.gov (United States)

Furness, James W; Verbeke, Joachim; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

2015-09-08

We present the self-consistent implementation of current-dependent (hybrid) meta-generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn-Sham current density functional theory (KS-CDFT). A unique feature of the nonperturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 au (∼235 kT) in strength. CDFT functionals based on the TPSS and B98 forms are investigated, and their performance is assessed by comparison with accurate coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) data. In the weak field regime, magnetic properties such as magnetizabilities and nuclear magnetic resonance shielding constants show modest but systematic improvements over generalized gradient approximations (GGA). However, in the strong field regime, the mGGA-based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T) data. In contrast to functionals based on the vorticity, these forms are found to be numerically stable, and their accuracy at high field suggests that the extension of mGGAs to CDFT via the generalized kinetic energy density should provide a useful starting point for further development of CDFT approximations.

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.

Electrocatalysis of borohydride oxidation: a review of density functional theory approach combined with experimental validation

International Nuclear Information System (INIS)

Sison Escaño, Mary Clare; Arevalo, Ryan Lacdao; Kasai, Hideaki; Gyenge, Elod

2014-01-01

The electrocatalysis of borohydride oxidation is a complex, up-to-eight-electron transfer process, which is essential for development of efficient direct borohydride fuel cells. Here we review the progress achieved by density functional theory (DFT) calculations in explaining the adsorption of BH 4 − on various catalyst surfaces, with implications for electrocatalyst screening and selection. Wherever possible, we correlate the theoretical predictions with experimental findings, in order to validate the proposed models and to identify potential directions for further advancements. (topical review)

Electrocatalysis of borohydride oxidation: a review of density functional theory approach combined with experimental validation

Science.gov (United States)

Sison Escaño, Mary Clare; Lacdao Arevalo, Ryan; Gyenge, Elod; Kasai, Hideaki

2014-09-01

The electrocatalysis of borohydride oxidation is a complex, up-to-eight-electron transfer process, which is essential for development of efficient direct borohydride fuel cells. Here we review the progress achieved by density functional theory (DFT) calculations in explaining the adsorption of BH4- on various catalyst surfaces, with implications for electrocatalyst screening and selection. Wherever possible, we correlate the theoretical predictions with experimental findings, in order to validate the proposed models and to identify potential directions for further advancements.

Theoretical Analysis of Polarized Structure Functions

CERN Document Server

Altarelli, Guido; Forte, Stefano; Ridolfi, G

1998-01-01

We review the analysis of polarized structure function data using perturbative QCD at next-to-leading order. We use the most recent experimental data to obtain updated results for polarized parton distributions, first moments and the strong coupling. We also discuss several theoretical issues involved in this analysis and in the interpretation of its results. Finally, we compare our results with other similar analyses in the recent literature.

Comments on the locality in density-functional theory

International Nuclear Information System (INIS)

Lindgren, Ingvar; Salomonson, Sten

2003-01-01

The 'locality hypothesis' in density-functional theory (DFT), implying that the functional derivative is equivalent to a multiplicative local function, forms the basis of models of Kohn-Sham type. This has been generally accepted by the community since the advent of the model, and has later been formally proved for a large class of functionals. The hypothesis has recently been questioned by Nesbet [Phys. Rev. A 58, R12 (1998) and Phys. Rev. A 65, 010502 (2001)], who claims that it fails for the kinetic-energy functional for a system with more than two noninteracting electrons with a nondegenerate ground state. This conclusion has been questioned by Gal [Phys. Rev. A 62, 044501 (2000)] and by Holas and March [Phys. Rev. A 64, 016501 (2001)]. We claim that the arguments of Nesbet are incorrect, since the orbital functional used for the kinetic energy is not a unique functional of the total density in the domain of unnormalized orbitals. We have demonstrated that with a proper definition of the kinetic energy, which is a unique density functional also in the unnormalized region, the derivative can be represented by a single local multiplicative function for all v-representable densities. Therefore, we consider the controversy connected with the issue raised by Nesbet as resolved. We believe that the proof of the differentiability given here can be extended to larger groups of DFT functionals, and works along these lines are in progress

Gluon density in nuclei

International Nuclear Information System (INIS)

Ayala, A.L.

1996-01-01

In this talk we present our detailed study (theory and numbers) on the shadowing corrections to the gluon structure functions for nuclei. Starting from rather controversial information on the nucleon structure function which is originated by the recent HERA data, we develop the Glauber approach for the gluon density in a nucleus based on Mueller formula and estimate the value of the shadowing corrections in this case. Then we calculate the first corrections to the Glauber approach and show that these corrections are big. Based on this practical observation we suggest the new evolution equation which takes into account the shadowing corrections and solve it. We hope to convince you that the new evolution equation gives a good theoretical tool to treat the shadowing corrections for the gluons density in a nucleus and, therefore, it is able to provide the theoretically reliable initial conditions for the time evolution of the nucleus-nucleus cascade. The initial conditions should be fixed both theoretically and phenomenologically before to attack such complicated problems as the mixture of hard and soft processes in nucleus-nucleus interactions at high energy or the theoretically reliable approach to hadron or/and parton cascades for high energy nucleus-nucleus interaction. 35 refs., 24 figs., 1 tab

Dissecting molecular descriptors into atomic contributions in density functional reactivity theory

International Nuclear Information System (INIS)

Rong, Chunying; Lu, Tian; Liu, Shubin

2014-01-01

Density functional reactivity theory (DFRT) employs the electron density of a molecule and its related quantities such as gradient and Laplacian to describe its structure and reactivity properties. Proper descriptions at both molecular (global) and atomic (local) levels are equally important and illuminating. In this work, we make use of Bader's zero-flux partition scheme and consider atomic contributions for a few global reactivity descriptors in DFRT, including the density-based quantification of steric effect and related indices. Earlier, we proved that these quantities are intrinsically correlated for atomic and molecular systems [S. B. Liu, J. Chem. Phys. 126, 191107 (2007); ibid. 126, 244103 (2007)]. In this work, a new basin-based integration algorithm has been implemented, whose reliability and effectiveness have been extensively examined. We also investigated a list of simple hydrocarbon systems and different scenarios of bonding processes, including stretching, bending, and rotating. Interesting changing patterns for the atomic and molecular values of these quantities have been revealed for different systems. This work not only confirms the strong correlation between these global reactivity descriptors for molecular systems, as theoretically proven earlier by us, it also provides new and unexpected changing patterns for their atomic values, which can be employed to understand the origin and nature of chemical phenomena

Dissecting molecular descriptors into atomic contributions in density functional reactivity theory

Energy Technology Data Exchange (ETDEWEB)

Rong, Chunying [Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China) and Key Laboratory of Resource Fine-Processing and Advanced Materials of Hunan Province, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081 (China); Lu, Tian [School of Chemical and Biological Engineering, University of Science and Technology Beijing, Beijing (China); Liu, Shubin, E-mail: shubin@email.unc.edu [Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China) and Key Laboratory of Resource Fine-Processing and Advanced Materials of Hunan Province, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081 (China); Research Computing Center, University of North Carolina, Chapel Hill, North Carolina 27599-3420 (United States)

2014-01-14

Density functional reactivity theory (DFRT) employs the electron density of a molecule and its related quantities such as gradient and Laplacian to describe its structure and reactivity properties. Proper descriptions at both molecular (global) and atomic (local) levels are equally important and illuminating. In this work, we make use of Bader's zero-flux partition scheme and consider atomic contributions for a few global reactivity descriptors in DFRT, including the density-based quantification of steric effect and related indices. Earlier, we proved that these quantities are intrinsically correlated for atomic and molecular systems [S. B. Liu, J. Chem. Phys. 126, 191107 (2007); ibid. 126, 244103 (2007)]. In this work, a new basin-based integration algorithm has been implemented, whose reliability and effectiveness have been extensively examined. We also investigated a list of simple hydrocarbon systems and different scenarios of bonding processes, including stretching, bending, and rotating. Interesting changing patterns for the atomic and molecular values of these quantities have been revealed for different systems. This work not only confirms the strong correlation between these global reactivity descriptors for molecular systems, as theoretically proven earlier by us, it also provides new and unexpected changing patterns for their atomic values, which can be employed to understand the origin and nature of chemical phenomena.

Time-Dependent Density Functional Theory Analysis of Triphenylamine-Functionalized Graphene Doped with Transition Metals for Photocatalytic Hydrogen Production.

Science.gov (United States)

Mota, Elder A V; Neto, Abel F G; Marques, Francisco C; Mota, Gunar V S; Martins, Marcelo G; Costa, Fabio L P; Borges, Rosivaldo S; Neto, Antonio M J C

2018-07-01

The electronic structures and optical properties of triphenylamine-functionalized graphene (G-TPA) doped with transition metals, using water as a solvent, were theoretically investigated to verify the efficiency of photocatalytic hydrogen production with the use of transition metals. This study was performed by Density Functional Theory and Time-dependent Density Functional Theory through Gaussian 09W software, adopting the B3LYP functional for all structures. The 6-31g(d) basis set was used for H, C and N atoms, and the LANL2DZ basis set for transition metals using the Effective Core Potentials method. Two approaches were adopted: (1) using single metallic dopants (Ni, Pd, Fe, Os and Pt) and (2) using combinations of Ni with the other dopants (NiPd, NiPt, NiFe and NiOs). The DOS spectra reveal an increase of accessible states in the valence shell, in addition to a gap decrease for all dopants. This doping also increases the absorption in the visible region of solar radiation where sunlight is most intense (400 nm to 700 nm), with additional absorption peaks. The results lead us to propose the G-TPA structures doped with Ni, Pd, Pt, NiPt or NiPd to be novel catalysts for the conversion of solar energy for photocatalytic hydrogen production, since they improve the absorption of solar energy in the range of interest for solar radiation; and act as reaction centers, reducing the required overpotential for hydrogen production from water.

Dynamic density functional theory with hydrodynamic interactions: Theoretical development and application in the study of phase separation in gas-liquid systems

International Nuclear Information System (INIS)

Kikkinides, E. S.; Monson, P. A.

2015-01-01

Building on recent developments in dynamic density functional theory, we have developed a version of the theory that includes hydrodynamic interactions. This is achieved by combining the continuity and momentum equations eliminating velocity fields, so the resulting model equation contains only terms related to the fluid density and its time and spatial derivatives. The new model satisfies simultaneously continuity and momentum equations under the assumptions of constant dynamic or kinematic viscosity and small velocities and/or density gradients. We present applications of the theory to spinodal decomposition of subcritical temperatures for one-dimensional and three-dimensional density perturbations for both a van der Waals fluid and for a lattice gas model in mean field theory. In the latter case, the theory provides a hydrodynamic extension to the recently studied dynamic mean field theory. We find that the theory correctly describes the transition from diffusive phase separation at short times to hydrodynamic behaviour at long times

Trivial constraints on orbital-free kinetic energy density functionals

Science.gov (United States)

Luo, Kai; Trickey, S. B.

2018-03-01

Approximate kinetic energy density functionals (KEDFs) are central to orbital-free density functional theory. Limitations on the spatial derivative dependencies of KEDFs have been claimed from differential virial theorems. We identify a central defect in the argument: the relationships are not true for an arbitrary density but hold only for the minimizing density and corresponding chemical potential. Contrary to the claims therefore, the relationships are not constraints and provide no independent information about the spatial derivative dependencies of approximate KEDFs. A simple argument also shows that validity for arbitrary v-representable densities is not restored by appeal to the density-potential bijection.

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.

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.

A density functional study on the adsorption of hydrogen molecule ...

Indian Academy of Sciences (India)

tive adsorption of H2 onto the minimum energy copper clusters by using the density ... theoretical study of molecular oxygen and atomic oxy- gen adsorption onto small ...... the values for all singlet spin states are zero, indicating that no ...

Covariant Density Functionals: time-odd channel investigated

International Nuclear Information System (INIS)

Afanasjev, A. V.; Abusara, H.

2009-01-01

The description of exotic nuclear systems and phenomena requires a detailed understanding of all channels of density functional theories. The role of time-odd mean fields, their evidence in experiment, and an accurate description of these fields are subject of current interest. Recent studies advanced the understanding of these fields in energy density functional theories based on the Skyrme force [1,2]. Time-odd mean fields are related to nuclear magnetism in covariant density functional (CDF) theories [3]. They arise from space-like components of vector mesons and Lorentz invariance requires that their coupling strengths are identical to that of time-like components. There were only few limited efforts to understand the role of time-odd mean fields in covariant density functional theory [4,5]. For example, the microscopic role of nuclear magnetism and its impact on rotational properties of nuclei has been studied in Ref. [5]. It is known that time-odd mean fields modify the angular momentum content of the single-particle orbitals and thus the moments of inertia, effective alignments, alignment gains at the band crossings and other physical observables. We aim on more detailed and systematic understanding of the role of time-odd mean fields in covariant density functional theory. This investigation covers both rotating and non-rotating systems. It is shown that contrary to the Skyrme energy density functionals time-odd mean fields of CDF theory always provide additional binding in the systems with broken time-reversal symmetry (rotating nuclei, odd mass nuclei). This additional binding increases with spin and has its maximum exactly at the terminating state [6], where it can reach several MeV. The impact of time-odd mean fields on the properties of rotating systems has been studied in a systematic way (as a function of particle number and deformation) across the nuclear chart [7]. In addition, this contribution extends these studies to non-rotating systems such as

Density functional theory of the electrical double layer: the RFD functional

International Nuclear Information System (INIS)

Gillespie, Dirk; Valisko, Monika; Boda, Dezso

2005-01-01

Density functional theory (DFT) of electrolytes is applied to the electrical double layer under a wide range of conditions. The ions are charged, hard spheres of different size and valence, and the wall creating the double layer is uncharged, weakly charged, and strongly charged. Under all conditions, the density and electrostatic potential profiles calculated using the recently proposed RFD electrostatic functional (Gillespie et al 2002 J. Phys.: Condens. Matter 14 12129; 2003 Phys. Rev. E 68 031503) compare well to Monte Carlo simulations. When the wall is strongly charged, the RFD functional results agree with the results of a simpler perturbative electrostatic DFT, but the two functionals' results qualitatively disagree when the wall is uncharged or weakly charged. The RFD functional reproduces these phenomena of weakly charged double layers. It also reproduces bulk thermodynamic quantities calculated from pair correlation functions

A Combined Theoretical and Experimental View on Valence and Conduction Band Densities of States of Lead Halide Perovskites

Science.gov (United States)

Kronik, Leeor; Endres, James; Egger, David A.; Kulbak, Michael; Kerner, Ross A.; Zhao, Lianfeng; Silver, Scott H.; Hodes, Gary; Rand, Barry P.; Cahen, David; Kahn, Antoine

We present results for the valence and conduction band density of states (DOS), measured via ultraviolet and inverse photoemission spectroscopies for three lead halide perovskites. Specifically, the DOS of MAPbI3, MAPbBr3, and CsPbBr3, grown on different substrates, are compared. Theoretical DOS, calculated via hybrid density functional theory and including spin-orbit coupling, are compared to experimental data. The agreement between experiment and theory, obtained after correcting the latter for quantitative discrepancies, leads to the identification of valence and conduction band spectral features. In particular, this comparison allows for precise determination of the energy position of the band edges, namely ionization energies and electron affinities of these materials. We find an unusually low DOS at the valence band maximum (VBM) of these systems, which confirms and generalizes previous findings of strong band dispersion and low DOS at the VBM of MAPbI3. This calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites.

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...

Orthogonal bases of radial functions for charge density refinements

International Nuclear Information System (INIS)

Restori, R.

1990-01-01

Charge density determination from X-ray measurements necessitates the evaluation of the Fourier-Bessel transforms of the radial functions used to expand the charge density. Analytical expressions are given here for four sets of orthogonal functions which can substitute for the 'traditional exponential functions' set in least-squares refinements. (orig.)

Dynamics of two-phase interfaces and surface tensions: A density-functional theory perspective

Science.gov (United States)

Yatsyshin, Petr; Sibley, David N.; Duran-Olivencia, Miguel A.; Kalliadasis, Serafim

2016-11-01

Classical density functional theory (DFT) is a statistical mechanical framework for the description of fluids at the nanoscale, where the inhomogeneity of the fluid structure needs to be carefully accounted for. By expressing the grand free-energy of the fluid as a functional of the one-body density, DFT offers a theoretically consistent and computationally accessible way to obtain two-phase interfaces and respective interfacial tensions in a ternary solid-liquid-gas system. The dynamic version of DFT (DDFT) can be rigorously derived from the Smoluchowsky picture of the dynamics of colloidal particles in a solvent. It is generally agreed that DDFT can capture the diffusion-driven evolution of many soft-matter systems. In this context, we use DDFT to investigate the dynamic behaviour of two-phase interfaces in both equilibrium and dynamic wetting and discuss the possibility of defining a time-dependent surface tension, which still remains in debate. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031 and from the Engineering and Physical Sciences Research Council of the UK via Grants No. EP/L027186 and EP/L020564.

Time-dependent density-functional tight-binding method with the third-order expansion of electron density.

Science.gov (United States)

Nishimoto, Yoshio

2015-09-07

We develop a formalism for the calculation of excitation energies and excited state gradients for the self-consistent-charge density-functional tight-binding method with the third-order contributions of a Taylor series of the density functional theory energy with respect to the fluctuation of electron density (time-dependent density-functional tight-binding (TD-DFTB3)). The formulation of the excitation energy is based on the existing time-dependent density functional theory and the older TD-DFTB2 formulae. The analytical gradient is computed by solving Z-vector equations, and it requires one to calculate the third-order derivative of the total energy with respect to density matrix elements due to the inclusion of the third-order contributions. The comparison of adiabatic excitation energies for selected small and medium-size molecules using the TD-DFTB2 and TD-DFTB3 methods shows that the inclusion of the third-order contributions does not affect excitation energies significantly. A different set of parameters, which are optimized for DFTB3, slightly improves the prediction of adiabatic excitation energies statistically. The application of TD-DFTB for the prediction of absorption and fluorescence energies of cresyl violet demonstrates that TD-DFTB3 reproduced the experimental fluorescence energy quite well.

Energy vs. density on paths toward exact density functionals

DEFF Research Database (Denmark)

Kepp, Kasper Planeta

2018-01-01

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...

Multicomponent density-functional theory for time-dependent systems

NARCIS (Netherlands)

Butriy, O.; Ebadi, H.; de Boeij, P. L.; van Leeuwen, R.; Gross, E. K. U.

2007-01-01

We derive the basic formalism of density functional theory for time-dependent electron-nuclear systems. The basic variables of this theory are the electron density in body-fixed frame coordinates and the diagonal of the nuclear N-body density matrix. The body-fixed frame transformation is carried

Improved Density Functional Tight Binding Potentials for Metalloid Aluminum Clusters

Science.gov (United States)

2016-06-01

unlimited IMPROVED DENSITY-FUNCTIONAL TIGHT BINDING POTENTIALS FOR METALLOID ALUMINUM CLUSTERS by Joon H. Kim June 2016 Thesis Advisor...DATES COVERED Master’s thesis 4. TITLE AND SUBTITLE IMPROVED DENSITY-FUNCTIONAL TIGHT BINDING POTENTIALS FOR METALLOID ALUMINUM CLUSTERS 5. FUNDING...repulsive potentials for use in density-functional tight binding (DFTB) simulations of low-valence aluminum metalloid clusters . These systems are under

Density-functional study of the compressed (2√3 × 2√3)R30°-CO overlayer on the ferromagnetic Co(0001) surface

Czech Academy of Sciences Publication Activity Database

Pick, Štěpán

2012-01-01

Roč. 606, 7-8 (2012), s. 692-696 ISSN 0039-6028 Institutional research plan: CEZ:AV0Z40400503 Keywords : density functional calculations * chemisorption * magnetic films Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.838, year: 2012

A density functional approach to ferrogels

Science.gov (United States)

Cremer, P.; Heinen, M.; Menzel, A. M.; Löwen, H.

2017-07-01

Ferrogels consist of magnetic colloidal particles embedded in an elastic polymer matrix. As a consequence, their structural and rheological properties are governed by a competition between magnetic particle-particle interactions and mechanical matrix elasticity. Typically, the particles are permanently fixed within the matrix, which makes them distinguishable by their positions. Over time, particle neighbors do not change due to the fixation by the matrix. Here we present a classical density functional approach for such ferrogels. We map the elastic matrix-induced interactions between neighboring colloidal particles distinguishable by their positions onto effective pairwise interactions between indistinguishable particles similar to a ‘pairwise pseudopotential’. Using Monte-Carlo computer simulations, we demonstrate for one-dimensional dipole-spring models of ferrogels that this mapping is justified. We then use the pseudopotential as an input into classical density functional theory of inhomogeneous fluids and predict the bulk elastic modulus of the ferrogel under various conditions. In addition, we propose the use of an ‘external pseudopotential’ when one switches from the viewpoint of a one-dimensional dipole-spring object to a one-dimensional chain embedded in an infinitely extended bulk matrix. Our mapping approach paves the way to describe various inhomogeneous situations of ferrogels using classical density functional concepts of inhomogeneous fluids.

Recent developments in LIBXC - A comprehensive library of functionals for density functional theory

Science.gov (United States)

Lehtola, Susi; Steigemann, Conrad; Oliveira, Micael J. T.; Marques, Miguel A. L.

2018-01-01

LIBXC is a library of exchange-correlation functionals for density-functional theory. We are concerned with semi-local functionals (or the semi-local part of hybrid functionals), namely local-density approximations, generalized-gradient approximations, and meta-generalized-gradient approximations. Currently we include around 400 functionals for the exchange, correlation, and the kinetic energy, spanning more than 50 years of research. Moreover, LIBXC is by now used by more than 20 codes, not only from the atomic, molecular, and solid-state physics, but also from the quantum chemistry communities.

A study of isotropic-nematic transition of quadrupolar Gay-Berne fluid using density-functional theory approach

Science.gov (United States)

Singh, Ram Chandra; Ram, Jokhan

2011-11-01

The effects of quadrupole moments on the isotropic-nematic (IN) phase transitions are studied using the density-functional theory (DFT) for a Gay-Berne (GB) fluid for a range of length-to-breadth parameters ? in the reduced temperature range ? . The pair-correlation functions of the isotropic phase, which enter into the DFT as input parameters are found by solving the Percus-Yevick integral equation theory. The method used involves an expansion of angle-dependent functions appearing in the integral equations in terms of spherical harmonics and the harmonic coefficients are obtained by an iterative algorithm. All the terms of harmonic coefficients which involve l indices up to less than or equal to 6 are considered. The numerical accuracy of the results depends on the number of spherical harmonic coefficients considered for each orientation-dependent function. As the length-to-breadth ratio of quadrupolar GB molecules is increased, the IN transition is seen to move to lower density (and pressure) at a given temperature. It has been observed that the DFT is good to study the IN transitions in such fluids. The theoretical results have also been compared with the computer simulation results wherever they are available.

Functional development in density functional theory for superconductors

Energy Technology Data Exchange (ETDEWEB)

Sanna, Antonio; Gross, E.K.U.; Essenberger, Frank [Max Planck Institute of Microstructure Physics, Halle (Saale) (Germany)

2015-07-01

Density functional theory for superconductors (SCDFT) is a fully parameter-free approach to superconductivity that allows for accurate predictions of critical temperature and properties of superconductors. We report on the most recent extensions of the method, in particular the development of new functionals to: (1) incorporate in a correct fashion Migdal's theorem; (2) compute the excitation spectrum; (3) include spin-fluctuation mediated pairing Applications and predictions are shown for a set of materials, including conventional and unconventional superconductors.

Density functional theory, comparative vibrational spectroscopic studies, highest occupied molecular orbital and lowest unoccupied molecular orbital analysis of Linezolid

Science.gov (United States)

Rajalakshmi, K.; Gunasekaran, S.; Kumaresan, S.

2015-06-01

The Fourier transform infrared spectra and Fourier transform Raman spectra of Linezolid have been recorded in the regions 4,000-400 and 4,000-100 cm-1, respectively. Utilizing the observed Fourier transform infrared spectra and Fourier transform Raman spectra data, a complete vibrational assignment and analysis of the fundamental modes of the compound have been carried out. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, have been calculated by density functional theory with 6-31G(d,p), 6-311G(d,p) and M06-2X/6-31G(d,p) levels. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of Linezolid is reported. Mulliken's net charges have also been calculated. Ultraviolet-visible spectrum of the title molecule has also been calculated using time-dependent density functional method. Besides, molecular electrostatic potential, highest occupied molecular orbital and lowest unoccupied molecular orbital analysis and several thermodynamic properties have been performed by the density functional theoretical method.

Equation satisfied by electron-electron mutual Coulomb repulsion energy density functional

OpenAIRE

Joubert, Daniel P.

2011-01-01

The electron-electron mutual Coulomb repulsion energy density functional satisfies an equation that links functionals and functional derivatives at N-electron and (N-1)-electron densities for densities determined from the same adiabatic scaled external potential for the N-electron system.

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

Self-contained filtered density function

Science.gov (United States)

Nouri, A. G.; Nik, M. B.; Givi, P.; Livescu, D.; Pope, S. B.

2017-09-01

The filtered density function (FDF) closure is extended to a "self-contained" format to include the subgrid-scale (SGS) statistics of all of the hydro-thermo-chemical variables in turbulent flows. These are the thermodynamic pressure, the specific internal energy, the velocity vector, and the composition field. In this format, the model is comprehensive and facilitates large-eddy simulation (LES) of flows at both low and high compressibility levels. A transport equation is developed for the joint pressure-energy-velocity-composition filtered mass density function (PEVC-FMDF). In this equation, the effect of convection appears in closed form. The coupling of the hydrodynamics and thermochemistry is modeled via a set of stochastic differential equation for each of the transport variables. This yields a self-contained SGS closure. For demonstration, LES is conducted of a turbulent shear flow with transport of a passive scalar. The consistency of the PEVC-FMDF formulation is established, and its overall predictive capability is appraised via comparison with direct numerical simulation (DNS) data.

Experiment and density functional theory analyses of GdTaO4 single crystal

Science.gov (United States)

Ding, Shoujun; Kinross, Ashlie; Wang, Xiaofei; Yang, Huajun; Zhang, Qingli; Liu, Wenpeng; Sun, Dunlu

2018-05-01

GdTaO4 is a type of excellent materials that can be used as scintillation, laser matrix as well as self-activated phosphor has generated significant interest. Whereas its band structure, electronic structure and optical properties are still need elucidation. To solve this intriguing problem, high-quality GdTaO4 single crystal (M-type) was grown successfully using Czochralski method. Its structure as well as optical properties was determined in experiment. Moreover, a systematic theoretical calculation based on the density function theory methods were performed on M-type and M‧-type GdTaO4 and their band structure, density of state as well as optical properties were obtained. Combine with the performed experiment results, the calculated results were proved with high reliability. Hence, the calculated results obtained in this work could provide a deep understanding of GdTaO4 material, which also useful for the further investigation on GdTaO4 material.

Density response to central electron heating: theoretical investigations and experimental observations in ASDEX Upgrade

Science.gov (United States)

Angioni, C.; Peeters, A. G.; Garbet, X.; Manini, A.; Ryter, F.; ASDEX Upgrade Team

2004-08-01

Theory of ion temperature gradient (ITG) and trapped electron modes (TEMs) is applied to the study of particle transport in experimental conditions with central electron heating. It is shown that in the unstable domain of TEMs, the electron thermodiffusive flux is directed outwards. By means of such a flux, a mechanism is identified likely to account for density flattening with central electron heating. Theoretical predictions are compared with experimental observations in ASDEX Upgrade. A parameter domain (including L- and H-mode plasmas) is identified, in which flattening with central electron heating is observed in the experiments. In general, this domain turns out to be the same domain in which the dominant plasma instability is a TEM. On the contrary, the dominant instability is an ITG in plasmas whose density profile is not affected significantly by central electron heating. The flattening predicted by quasi-linear theory for low density L-mode plasmas is too small compared to the experimental observations. At very high density, even when the dominant instability is an ITG, electron heating can provide density flattening, via the coupling with the ion heat channel. In these conditions the anomalous diffusivity increases in response to the increased ion heat flux, while the large collisionality makes the anomalous pinch small and the Ware pinch important.

Microscopically based energy density functionals for nuclei using the density matrix expansion. II. Full optimization and validation

Science.gov (United States)

Navarro Pérez, R.; Schunck, N.; Dyhdalo, A.; Furnstahl, R. J.; Bogner, S. K.

2018-05-01

Background: Energy density functional methods provide a generic framework to compute properties of atomic nuclei starting from models of nuclear potentials and the rules of quantum mechanics. Until now, the overwhelming majority of functionals have been constructed either from empirical nuclear potentials such as the Skyrme or Gogny forces, or from systematic gradient-like expansions in the spirit of the density functional theory for atoms. Purpose: We seek to obtain a usable form of the nuclear energy density functional that is rooted in the modern theory of nuclear forces. We thus consider a functional obtained from the density matrix expansion of local nuclear potentials from chiral effective field theory. We propose a parametrization of this functional carefully calibrated and validated on selected ground-state properties that is suitable for large-scale calculations of nuclear properties. Methods: Our energy functional comprises two main components. The first component is a non-local functional of the density and corresponds to the direct part (Hartree term) of the expectation value of local chiral potentials on a Slater determinant. Contributions to the mean field and the energy of this term are computed by expanding the spatial, finite-range components of the chiral potential onto Gaussian functions. The second component is a local functional of the density and is obtained by applying the density matrix expansion to the exchange part (Fock term) of the expectation value of the local chiral potential. We apply the UNEDF2 optimization protocol to determine the coupling constants of this energy functional. Results: We obtain a set of microscopically constrained functionals for local chiral potentials from leading order up to next-to-next-to-leading order with and without three-body forces and contributions from Δ excitations. These functionals are validated on the calculation of nuclear and neutron matter, nuclear mass tables, single-particle shell structure

Modeling charged defects inside density functional theory band gaps

International Nuclear Information System (INIS)

Schultz, Peter A.; Edwards, Arthur H.

2014-01-01

Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem

Graphene on metals: A van der Waals density functional study

DEFF Research Database (Denmark)

Vanin, Marco; Mortensen, Jens Jørgen; Kelkkanen, Kari André

2010-01-01

We use density functional theory (DFT) with a recently developed van der Waals density functional (vdW-DF) to study the adsorption of graphene on Co, Ni, Pd, Ag, Au, Cu, Pt, and Al(111) surfaces. In contrast to the local-density approximation (LDA) which predicts relatively strong binding for Ni...

Accurate Energies and Structures for Large Water Clusters Using the X3LYP Hybrid Density Functional

OpenAIRE

Su, Julius T.; Xu, Xin; Goddard, William A., III

2004-01-01

We predict structures and energies of water clusters containing up to 19 waters with X3LYP, an extended hybrid density functional designed to describe noncovalently bound systems as accurately as covalent systems. Our work establishes X3LYP as the most practical ab initio method today for calculating accurate water cluster structures and energies. We compare X3LYP/aug-cc-pVTZ energies to the most accurate theoretical values available (n = 2−6, 8), MP2 with basis set superposition error (BSSE)...

Density-functional study of photoinduced water splitting

International Nuclear Information System (INIS)

Martínez Mesa, Aliezer; Rodríguez Hernández, Fermín; Seifert, Gotthard; Tranca, Diana

2015-01-01

We investigate the dynamics of water splitting on dye-sensitized metal (Ti, Cu) oxide surfaces, induced by direct sunlight excitation. In this study, we will consider the typical photoexcitation-followed-by-injection scheme, treating electron-injection and water splitting dynamics as independent events. The simultaneous modeling of the molecular motion and the quantum nonadiabatic transitions is achieved via the computation of the low-lying electronic states along several alternative reaction paths. Electronic structure calculations are based on a B3LYP-DFT Hamiltonian. The proposed approach combines an atomistic description of the reactants and of the immediate region of the surface, while the vibrational dynamics of the substrate is modeled as an effective bath leading to dissipation effects. The use of density-functional theory to solve the many- body electronic problem allows investigating the atomic motion of the water molecules and of a representative part of the substrate, thereby providing a theoretical and computational model capable to account simultaneously for the molecular character of the dye molecule and for the bulk properties of the surface. Furthermore, the insight emerging from this fundamental modeling can be used to optimize the chemical composition of the system to attain high incident-photon-flux-to-hydrogen-yield ratios. (full text)

Information density converges in dialogue: Towards an information-theoretic model.

Science.gov (United States)

Xu, Yang; Reitter, David

2018-01-01

The principle of entropy rate constancy (ERC) states that language users distribute information such that words tend to be equally predictable given previous contexts. We examine the applicability of this principle to spoken dialogue, as previous findings primarily rest on written text. The study takes into account the joint-activity nature of dialogue and the topic shift mechanisms that are different from monologue. It examines how the information contributions from the two dialogue partners interactively evolve as the discourse develops. The increase of local sentence-level information density (predicted by ERC) is shown to apply to dialogue overall. However, when the different roles of interlocutors in introducing new topics are identified, their contribution in information content displays a new converging pattern. We draw explanations to this pattern from multiple perspectives: Casting dialogue as an information exchange system would mean that the pattern is the result of two interlocutors maintaining their own context rather than sharing one. Second, we present some empirical evidence that a model of Interactive Alignment may include information density to explain the effect. Third, we argue that building common ground is a process analogous to information convergence. Thus, we put forward an information-theoretic view of dialogue, under which some existing theories of human dialogue may eventually be unified. Copyright © 2017 Elsevier B.V. All rights reserved.

Nuclear level density

International Nuclear Information System (INIS)

Cardoso Junior, J.L.

1982-10-01

Experimental data show that the number of nuclear states increases rapidly with increasing excitation energy. The properties of highly excited nuclei are important for many nuclear reactions, mainly those that go via processes of the compound nucleus type. In this case, it is sufficient to know the statistical properties of the nuclear levels. First of them is the function of nuclear levels density. Several theoretical models which describe the level density are presented. The statistical mechanics and a quantum mechanics formalisms as well as semi-empirical results are analysed and discussed. (Author) [pt

Bayesian error estimation in density-functional theory

DEFF Research Database (Denmark)

Mortensen, Jens Jørgen; Kaasbjerg, Kristen; Frederiksen, Søren Lund

2005-01-01

We present a practical scheme for performing error estimates for density-functional theory calculations. The approach, which is based on ideas from Bayesian statistics, involves creating an ensemble of exchange-correlation functionals by comparing with an experimental database of binding energies...

Theoretical investigation on structural and electronic properties of PdO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Viswanathan, E.; Sundareswari, M., E-mail: sund-uday@yahoo.co.in, E-mail: sundare65@gmail.com; Jayalakshmi, D. S.; Manjula, M. [Department of Physics, Sathyabama University, Jeppiaar Nagar, OMR, Chennai-600119 (India)

2015-06-24

Theoretical studies on rutile type Palladium Dioxide were carried out with the aim of analyzing structural and electronic properties at ambient condition using the first principle calculation based on density functional theory. Within the framework of density functional theory, we used full potential linearized augmented plane wave method(FP-LAPW) in Wien 2k code. The exchange and correlation effect is treated with generalized gradient approximation (GGA) using the Perdew, Burke and Eruzeroff form. The charge density plots, density of states and band structure are plotted and discussed.

Nuclear energy density functional from chiral pion-nucleon dynamics revisited

Science.gov (United States)

Kaiser, N.; Weise, W.

2010-05-01

We use a recently improved density-matrix expansion to calculate the nuclear energy density functional in the framework of in-medium chiral perturbation theory. Our calculation treats systematically the effects from 1 π-exchange, iterated 1 π-exchange, and irreducible 2 π-exchange with intermediate Δ-isobar excitations, including Pauli-blocking corrections up to three-loop order. We find that the effective nucleon mass M(ρ) entering the energy density functional is identical to the one of Fermi-liquid theory when employing the improved density-matrix expansion. The strength F(ρ) of the ( surface-term as provided by the pion-exchange dynamics is in good agreement with that of phenomenological Skyrme forces in the density region ρ/2short-range spin-orbit interaction. The strength function F(ρ) multiplying the square of the spin-orbit density comes out much larger than in phenomenological Skyrme forces and it has a pronounced density dependence.

Structure of cylindrical electric double layers: Comparison of density functional and modified Poisson-Boltzmann theories with Monte Carlo simulations

Directory of Open Access Journals (Sweden)

V.Dorvilien

2013-01-01

Full Text Available The structure of cylindrical double layers is studied using a modified Poisson Boltzmann theory and the density functional approach. In the model double layer the electrode is a cylindrical polyion that is infinitely long, impenetrable, and uniformly charged. The polyion is immersed in a sea of equi-sized rigid ions embedded in a dielectric continuum. An in-depth comparison of the theoretically predicted zeta potentials, the mean electrostatic potentials, and the electrode-ion singlet density distributions is made with the corresponding Monte Carlo simulation data. The theories are seen to be consistent in their predictions that include variations in ionic diameters, electrolyte concentrations, and electrode surface charge densities, and are also able to reproduce well some new and existing Monte Carlo results.

The heat current density correlation function: sum rules and thermal conductivity

International Nuclear Information System (INIS)

Singh, Shaminder; Tankeshwar, K; Pathak, K N; Ranganathan, S

2006-01-01

Expressions for the second and fourth sum rules of the heat current density correlation function have been derived in an appropriate ensemble. The thermal conductivity of Lennard-Jones fluids has been calculated using these sum rules for the heat current density correlation function and the Gaussian form of the memory function. It is found that the results obtained for the thermal conductivity are in good agreement with the molecular dynamics simulation results over a wide range of densities and temperatures. Earlier results obtained using the energy current density correlation function are also discussed

The heat current density correlation function: sum rules and thermal conductivity

Energy Technology Data Exchange (ETDEWEB)

Singh, Shaminder [Department of Physics, Panjab University, Chandigarh-160 014 (India); Tankeshwar, K [Department of Physics, Panjab University, Chandigarh-160 014 (India); Pathak, K N [Department of Physics, Panjab University, Chandigarh-160 014 (India); Ranganathan, S [Department of Physics, Royal Military College, Kingston, ON, K7K 7B4 (Canada)

2006-02-01

Expressions for the second and fourth sum rules of the heat current density correlation function have been derived in an appropriate ensemble. The thermal conductivity of Lennard-Jones fluids has been calculated using these sum rules for the heat current density correlation function and the Gaussian form of the memory function. It is found that the results obtained for the thermal conductivity are in good agreement with the molecular dynamics simulation results over a wide range of densities and temperatures. Earlier results obtained using the energy current density correlation function are also discussed.

Density functional theory study on the electronic structure of UAl3 and USn3

International Nuclear Information System (INIS)

Tan Mingqiu; Tao Xiangming; Xu Xiaojun; Cai Jianqiu

2003-01-01

Authors report an ab initio study on the electronic properties of 5f states in U X 3 (X=Al, Sn) by full-potential linear muffin-tin orbitals L(S)DA calculations. The relativistic effects which are quite remarkable for heavy atoms such as U, have been treated by using scalar relativistic and spin-orbital coupling corrections. The calculations presented in this article have addressed following issues: firstly, the numerical results illustrates the different U 5f itineracy in UAl 3 and USn 3 qualitatively, and then the heavy fermion behavior of USn 3 ; secondly, using Stuttgart-fatband analysis, authors have confirmed the above conclusion quantitatively. In addition to the above results, the calculation involved in this research has resolved the discrepancy between previous density functional theory studies on these compounds, especially the band structure dispersion in M-X direction of simple cubic USn 3 . In conclusion, this study has approached a more precise description for these uranium compounds on the basis of modern density functional theory calculation and described USn 3 as a heavy fermion system due to its localized U 5f electronic states theoretically

A classical density functional theory of ionic liquids.

Science.gov (United States)

Forsman, Jan; Woodward, Clifford E; Trulsson, Martin

2011-04-28

We present a simple, classical density functional approach to the study of simple models of room temperature ionic liquids. Dispersion attractions as well as ion correlation effects and excluded volume packing are taken into account. The oligomeric structure, common to many ionic liquid molecules, is handled by a polymer density functional treatment. The theory is evaluated by comparisons with simulations, with an emphasis on the differential capacitance, an experimentally measurable quantity of significant practical interest.

Theoretical foundations of functional data analysis, with an introduction to linear operators

CERN Document Server

Hsing, Tailen

2015-01-01

Theoretical Foundations of Functional Data Analysis, with an Introduction to Linear Operators provides a uniquely broad compendium of the key mathematical concepts and results that are relevant for the theoretical development of functional data analysis (FDA).The self-contained treatment of selected topics of functional analysis and operator theory includes reproducing kernel Hilbert spaces, singular value decomposition of compact operators on Hilbert spaces and perturbation theory for both self-adjoint and non self-adjoint operators. The probabilistic foundation for FDA is described from the

Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

Science.gov (United States)

Zhou, Bin; Hu, Zhubin; Jiang, Yanrong; He, Xiao; Sun, Zhenrong; Sun, Haitao

2018-05-01

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20n H20 (n  =  2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–ε HOMO and –ε LUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.

Self-contained filtered density function

International Nuclear Information System (INIS)

Nouri, Arash G.; Pope, Stephen B.

2017-01-01

The filtered density function (FDF) closure is extended to a “self-contained” format to include the subgrid-scale (SGS) statistics of all of the hydro-thermo-chemical variables in turbulent flows. These are the thermodynamic pressure, the specific internal energy, the velocity vector, and the composition field. In this format, the model is comprehensive and facilitates large-eddy simulation (LES) of flows at both low and high compressibility levels. A transport equation is developed for the joint pressure-energy-velocity-composition filtered mass density function (PEVC-FMDF). In this equation, the effect of convection appears in closed form. The coupling of the hydrodynamics and thermochemistry is modeled via a set of stochastic differential equation for each of the transport variables. This yields a self-contained SGS closure. We demonstrated how LES is conducted of a turbulent shear flow with transport of a passive scalar. Finally, the consistency of the PEVC-FMDF formulation is established, and its overall predictive capability is appraised via comparison with direct numerical simulation (DNS) data.

Density functional theory calculations establish the experimental evidence of the DX center atomic structure in CdTe.

Science.gov (United States)

Lany, Stephan; Wolf, Herbert; Wichert, Thomas

2004-06-04

The In DX center and the DX-like configuration of the Cd host atom in CdTe are investigated using density functional theory. The simultaneous calculation of the atomic structure and the electric field gradient (EFG) allows one to correlate the theoretically predicted structure of the DX center with an experimental observable, namely, the EFG obtained from radioactive 111In/111Cd probe atoms in In doped CdTe. In this way, the experimental identification of the DX center structure is established.

One-nucleon removal reactions as a test of overlap functions from the one-body density matrix calculations

International Nuclear Information System (INIS)

Dimitrova, S.S.; Gaidarov, M.K.; Antonov, A.N.; Stoitsov, M.V.; Hodgson, P.E; Lukyanov, V.K.; Zemlyanaya, E.V.; Krumova, G.Z.

1997-01-01

Overlap functions and spectroscopic factors extracted from a model one-body density matrix (OBDM) accounting for short-range nucleon-nucleon correlations are used to calculate differential cross sections of (p, d) reactions and the momentum distributions of transitions to single-particle states in 16 O and 40 Ca. A comparison between the experimental (p, d) and (e, e'p) data, their DWBA and CDWIA analyses and the OBDM calculations is made. Our theoretical predictions for the spectroscopic factors are compared with the empirically extracted ones. It is shown that the overlap functions obtained within the Jastrow correlation method are applicable to the description of the quantities considered. (author)

Doping effects in InN/GaN short-period quantum well structures-Theoretical studies based on density functional methods

Science.gov (United States)

Strak, Pawel; Kempisty, Pawel; Sakowski, Konrad; Krukowski, Stanislaw

2014-09-01

Density functional theory studies were conducted to determine an influence of the carrier concentration on the optical and electronic properties of InN/GaN superlattice system. The oscillator strength values, energy gaps and the band profiles were obtained. The band profiles were found to be strongly affected for technically possible heavy n-type doping while for p-type doping the carrier influence, both screening and band shift, is negligible. Blue shift of the transition energy between conduction band minima and valence band maxima was observed for high concentrations of both type carriers.

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.

Benchmark density functional theory calculations for nanoscale conductance

DEFF Research Database (Denmark)

Strange, Mikkel; Bækgaard, Iben Sig Buur; Thygesen, Kristian Sommer

2008-01-01

We present a set of benchmark calculations for the Kohn-Sham elastic transmission function of five representative single-molecule junctions. The transmission functions are calculated using two different density functional theory methods, namely an ultrasoft pseudopotential plane-wave code...

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

Surface modification of carbon nanotubes using 3-aminopropyltriethoxysilane to improve mechanical properties of nanocomposite based polymer matrix: Experimental and Density functional theory study

Science.gov (United States)

Hamed Mashhadzadeh, A.; Fereidoon, Ab.; Ghorbanzadeh Ahangari, M.

2017-10-01

In current study we combined theoretical and experimental studies to evaluate the effect of functionalization and silanization on mechanical behavior of polymer-based/CNT nanocomposites. Epoxy was selected as thermoset polymer, polypropylene and poly vinyl chloride were selected as thermoplastic polymers. The whole procedure is divided to two sections . At first we applied density functional theory (DFT) to analyze the effect of functionalization on equilibrium distance and adsorption energy of unmodified, functionalized by sbnd OH group and silanized epoxy/CNT, PP/CNT and PVC/CNT nanocomposites and the results showed that functionalization increased adsorption energy and reduced the equilibrium distance in all studied nanocomposites and silanization had higher effect comparing to OH functionalizing. Then we prepared experimental samples of all mentioned nanocomposites and tested their tensile and flexural strength properties. The obtained results showed that functionalization increased the studied mechanical properties in all evaluated nanocomposites. Finally we compared the results of experimental and theoretical sections with each other and estimated a suitable agreement between these parts.

A classical density functional investigation of nucleation

International Nuclear Information System (INIS)

Ghosh, Satinath; Ghosh, Swapan K.

2009-01-01

Study of nucleation and growth phenomena in condensation is of prime importance in various applications such as crystal growth, nanoparticle synthesis, pattern formation etc. The knowledge of nucleation barrier in condensation is necessary to control the nucleation kinetics, size of the nanoparticles etc. Classical nucleation theory (CNT) assumes the density of the drop as bulk density irrespective of the size of the drop and overestimates the nucleation barrier. Here we are interested in solving the problem analytically using density functional theory (DFT) with square gradient approximation along the lines of Cahn and Hilliard. Nucleation barrier and density profile obtained in this work are consistent with other works based on nonclassical theory. (author)

Nonlocal exchange and kinetic-energy density functionals for electronic systems

International Nuclear Information System (INIS)

Glossman, M.D.; Rubio, A.; Balbas, L.C.; Alonso, J.A.

1992-01-01

The nonlocal weighted density approximation (WDA) to the exchange and kinetic-energy functionals of many electron systems proposed several years ago by Alonso and Girifalco is used to compute, within the framework of density functional theory, the ground-state electronic density and total energy of noble gas atoms and of neutral jellium-like sodium clusters containing up to 500 atoms. These results are compared with analogous calculations using the well known Thomas-Fermi-Weizsacker-Dirac (TFWD) approximations for the kinetic (TFW) and exchange (D) energy density functionals. An outstanding improvement of the total and exchange energies, of the density at the nucleus and of the expectation values is obtained for atoms within the WDA scheme. For sodium clusters the authors notice a sizeable contribution of the nonlocal effects to the total energy and to the density profiles. In the limit of very large clusters these effects should affect the surface energy of the bulk metal

Remarks on time-dependent [current]-density functional theory for open quantum systems.

Science.gov (United States)

Yuen-Zhou, Joel; Aspuru-Guzik, Alán

2013-08-14

Time-dependent [current]-density functional theory for open quantum systems (OQS) has emerged as a formalism that can incorporate dissipative effects in the dynamics of many-body quantum systems. Here, we review and clarify some formal aspects of these theories that have been recently questioned in the literature. In particular, we provide theoretical support for the following conclusions: (1) contrary to what we and others had stated before, within the master equation framework, there is in fact a one-to-one mapping between vector potentials and current densities for fixed initial state, particle-particle interaction, and memory kernel; (2) regardless of the first conclusion, all of our recently suggested Kohn-Sham (KS) schemes to reproduce the current and particle densities of the original OQS, and in particular, the use of a KS closed driven system, remains formally valid; (3) the Lindblad master equation maintains the positivity of the density matrix regardless of the time-dependence of the Hamiltonian or the dissipation operators; (4) within the stochastic Schrödinger equation picture, a one-to-one mapping from stochastic vector potential to stochastic current density for individual trajectories has not been proven so far, except in the case where the vector potential is the same for every member of the ensemble, in which case, it reduces to the Lindblad master equation picture; (5) master equations may violate certain desired properties of the density matrix, such as positivity, but they remain as one of the most useful constructs to study OQS when the environment is not easily incorporated explicitly in the calculation. The conclusions support our previous work as formally rigorous, offer new insights into it, and provide a common ground to discuss related theories.

Higher-accuracy van der Waals density functional

DEFF Research Database (Denmark)

Lee, Kyuho; Murray, Éamonn D.; Kong, Lingzhu

2010-01-01

We propose a second version of the van der Waals density functional of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], employing a more accurate semilocal exchange functional and the use of a large-N asymptote gradient correction in determining the vdW kernel. The predicted binding energy...

A comparative study of density functional and density functional tight binding calculations of defects in graphene

Energy Technology Data Exchange (ETDEWEB)

Zobelli, Alberto [Laboratoire de Physique des Solides, Univ. Paris Sud, CNRS UMR, Orsay (France); Ivanovskaya, Viktoria; Wagner, Philipp; Yaya, Abu; Ewels, Chris P. [Institut des Materiaux Jean Rouxel (IMN), CNRS UMR, University of Nantes (France); Suarez-Martinez, Irene [Nanochemistry Research Institute, Curtin University of Technology, Perth, Western Australia (Australia)

2012-02-15

The density functional tight binding approach (DFTB) is well adapted for the study of point and line defects in graphene based systems. After briefly reviewing the use of DFTB in this area, we present a comparative study of defect structures, energies, and dynamics between DFTB results obtained using the dftb+ code, and density functional results using the localized Gaussian orbital code, AIMPRO. DFTB accurately reproduces structures and energies for a range of point defect structures such as vacancies and Stone-Wales defects in graphene, as well as various unfunctionalized and hydroxylated graphene sheet edges. Migration barriers for the vacancy and Stone-Wales defect formation barriers are accurately reproduced using a nudged elastic band approach. Finally we explore the potential for dynamic defect simulations using DFTB, taking as an example electron irradiation damage in graphene. DFTB-MD derived sputtering energy threshold map for a carbon atom in a graphene plane. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

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.

Postfragmentation density function for bacterial aggregates in laminar flow.

Science.gov (United States)

Byrne, Erin; Dzul, Steve; Solomon, Michael; Younger, John; Bortz, David M

2011-04-01

The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation. ©2011 American Physical Society

Linking density functional and mode coupling models for supercooled liquids.

Science.gov (United States)

Premkumar, Leishangthem; Bidhoodi, Neeta; Das, Shankar P

2016-03-28

We compare predictions from two familiar models of the metastable supercooled liquid, respectively, constructed with thermodynamic and dynamic approaches. In the so called density functional theory the free energy F[ρ] of the liquid is a functional of the inhomogeneous density ρ(r). The metastable state is identified as a local minimum of F[ρ]. The sharp density profile characterizing ρ(r) is identified as a single particle oscillator, whose frequency is obtained from the parameters of the optimum density function. On the other hand, a dynamic approach to supercooled liquids is taken in the mode coupling theory (MCT) which predict a sharp ergodicity-non-ergodicity transition at a critical density. The single particle dynamics in the non-ergodic state, treated approximately, represents a propagating mode whose characteristic frequency is computed from the corresponding memory function of the MCT. The mass localization parameters in the above two models (treated in their simplest forms) are obtained, respectively, in terms of the corresponding natural frequencies depicted and are shown to have comparable magnitudes.

Linking density functional and mode coupling models for supercooled liquids

Energy Technology Data Exchange (ETDEWEB)

Premkumar, Leishangthem; Bidhoodi, Neeta; Das, Shankar P. [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India)

2016-03-28

We compare predictions from two familiar models of the metastable supercooled liquid, respectively, constructed with thermodynamic and dynamic approaches. In the so called density functional theory the free energy F[ρ] of the liquid is a functional of the inhomogeneous density ρ(r). The metastable state is identified as a local minimum of F[ρ]. The sharp density profile characterizing ρ(r) is identified as a single particle oscillator, whose frequency is obtained from the parameters of the optimum density function. On the other hand, a dynamic approach to supercooled liquids is taken in the mode coupling theory (MCT) which predict a sharp ergodicity-non-ergodicity transition at a critical density. The single particle dynamics in the non-ergodic state, treated approximately, represents a propagating mode whose characteristic frequency is computed from the corresponding memory function of the MCT. The mass localization parameters in the above two models (treated in their simplest forms) are obtained, respectively, in terms of the corresponding natural frequencies depicted and are shown to have comparable magnitudes.

Adsorption properties of AlN on Si(111) surface: A density functional study

Science.gov (United States)

Yuan, Yinmei; Zuo, Ran; Mao, Keke; Tang, Binlong; Zhang, Zhou; Liu, Jun; Zhong, Tingting

2018-04-01

In the process of preparing GaN on Si substrate by MOCVD, an AlN buffer layer is very important. In this study, we conducted density functional theory calculations on the adsorption of AlN molecule on Si(111)-(2 × 2) surface, with the AlN molecule located horizontally or vertically above Si(111) surface at different adsorption sites. The calculations revealed that the lowest adsorption energy was at the N-top-Al-bridge site in the horizontal configuration, with the narrowest band gap, indicating that it was the most preferential adsorption growth status of AlN. In the vertical configurations, N adatom was more reactive and convenient to form bonds with the topmost Si atoms than Al adatom. When the N-end of the AlN molecule was located downward, the hollow site was the preferred adsorption site; when the Al-end was located downward, the bridge site was the most energetically favorable. Moreover, we investigated some electronic properties such as partial density of states, electron density difference, Mulliken populations, etc., revealing the microscale mechanism for AlN adsorption on Si(111) surface and providing theoretical support for adjusting the processing parameters during AlN or GaN production.

A time-dependent density functional theory investigation of plasmon resonances of linear Au atomic chains

International Nuclear Information System (INIS)

Liu Dan-Dan; Zhang Hong

2011-01-01

We report theoretical studies on the plasmon resonances in linear Au atomic chains by using ab initio time-dependent density functional theory. The dipole responses are investigated each as a function of chain length. They converge into a single resonance in the longitudinal mode but split into two transverse modes. As the chain length increases, the longitudinal plasmon mode is redshifted in energy while the transverse modes shift in the opposite direction (blueshifts). In addition, the energy gap between the two transverse modes reduces with chain length increasing. We find that there are unique characteristics, different from those of other metallic chains. These characteristics are crucial to atomic-scale engineering of single-molecule sensing, optical spectroscopy, and so on. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Modelling energy level alignment at organic interfaces and density functional theory

DEFF Research Database (Denmark)

Flores, F.; Ortega, J.; Vazquez, Patricia

2009-01-01

A review of our theoretical understanding of the band alignment at organic interfaces is presented with particular emphasis on the metal/organic (MO) case. The unified IDIS (induced density of interface states) and the ICT (integer charge transfer) models are reviewed and shown to describe qualit...

Teaching Density Functional Theory Through Experiential Learning

International Nuclear Information System (INIS)

Narasimhan, Shobhana

2015-01-01

Today, quantum mechanical density functional theory is often the method of choice for performing accurate calculations on atomic, molecular and condensed matter systems. Here, I share some of my experiences in teaching the necessary basics of solid state physics, as well as the theory and practice of density functional theory, in a number of workshops held in developing countries over the past two decades. I discuss the advantages of supplementing the usual mathematically formal teaching methods, characteristic of graduate courses, with the use of visual imagery and analogies. I also describe a successful experiment we carried out, which resulted in a joint publication co-authored by 67 lecturers and students participating in a summer school. (paper)

A Density Functional Theory Study of Doped Tin Monoxide as a Transparent p-type Semiconductor

KAUST Repository

Bianchi Granato, Danilo

2012-05-01

In the pursuit of enhancing the electronic properties of transparent p-type semiconductors, this work uses density functional theory to study the effects of doping tin monoxide with nitrogen, antimony, yttrium and lanthanum. An overview of the theoretical concepts and a detailed description of the methods employed are given, including a discussion about the correction scheme for charged defects proposed by Freysoldt and others [Freysoldt 2009]. Analysis of the formation energies of the defects points out that nitrogen substitutes an oxygen atom and does not provide charge carriers. On the other hand, antimony, yttrium, and lanthanum substitute a tin atom and donate n-type carriers. Study of the band structure and density of states indicates that yttrium and lanthanum improves the hole mobility. Present results are in good agreement with available experimental works and help to improve the understanding on how to engineer transparent p-type materials with higher hole mobilities.

Theoretical study of n-alkane adsorption on metal surfaces

DEFF Research Database (Denmark)

Morikawa, Yoshitada; Ishii, Hisao; Seki, Kazuhiko

2004-01-01

The interaction between n-alkane and metal surfaces has been studied by means of density-functional theoretical calculations within a generalized gradient approximation (GGA). We demonstrate that although the GGA cannot reproduce the physisorption energy well, our calculations can reproduce the e...

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...

Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones.

Science.gov (United States)

Sancho-García, J C

2012-05-07

A set of N-heteroquinones, deriving from oligoacenes, have been recently proposed as n-type organic semiconductors with high electron mobilities in thin-film transistors. Generally speaking, this class of compounds self-assembles in neighboring π-stacks linked by weak hydrogen bonds. We aim at theoretically characterizing here the sequential charge transport (hopping) process expected to take place across these arrays of molecules. To do so, we need to accurately address the preferred packing of these materials simultaneously to single-molecule properties related to charge-transfer events, carefully employing dispersion-corrected density functional theory methods to accurately extract the key molecular parameters governing this phenomenon at the nanoscale. This study confirms the great deal of interest around these compounds, since controlled functionalization of model molecules (i.e., pentacene) allows to efficiently tune the corresponding charge mobilities, and the capacity of modern quantum-chemical methods to predict it after rationalizing the underlying structure-property relationships.

Source-Free Exchange-Correlation Magnetic Fields in Density Functional Theory.

Science.gov (United States)

Sharma, S; Gross, E K U; Sanna, A; Dewhurst, J K

2018-03-13

Spin-dependent exchange-correlation energy functionals in use today depend on the charge density and the magnetization density: E xc [ρ, m]. However, it is also correct to define the functional in terms of the curl of m for physical external fields: E xc [ρ,∇ × m]. The exchange-correlation magnetic field, B xc , then becomes source-free. We study this variation of the theory by uniquely removing the source term from local and generalized gradient approximations to the functional. By doing so, the total Kohn-Sham moments are improved for a wide range of materials for both functionals. Significantly, the moments for the pnictides are now in good agreement with experiment. This source-free method is simple to implement in all existing density functional theory codes.

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) ...

Density functional and neural network analysis

DEFF Research Database (Denmark)

Jalkanen, K. J.; Suhai, S.; Bohr, Henrik

1997-01-01

Density functional theory (DFT) calculations have been carried out for hydrated L-alanine, L-alanyl-L-alanine and N-acetyl L-alanine N'-methylamide and examined with respect to the effect of water on the structure, the vibrational frequencies, vibrational absorption (VA) and vibrational circular...

Nuclear energy density functional from chiral pion-nucleon dynamics revisited

OpenAIRE

Kaiser, N.; Weise, W.

2009-01-01

We use a recently improved density-matrix expansion to calculate the nuclear energy density functional in the framework of in-medium chiral perturbation theory. Our calculation treats systematically the effects from $1\\pi$-exchange, iterated $1\\pi$-exchange, and irreducible $2\\pi$-exchange with intermediate $\\Delta$-isobar excitations, including Pauli-blocking corrections up to three-loop order. We find that the effective nucleon mass $M^*(\\rho)$ entering the energy density functional is iden...

On the expected value and variance for an estimator of the spatio-temporal product density function

DEFF Research Database (Denmark)

Rodríguez-Corté, Francisco J.; Ghorbani, Mohammad; Mateu, Jorge

Second-order characteristics are used to analyse the spatio-temporal structure of the underlying point process, and thus these methods provide a natural starting point for the analysis of spatio-temporal point process data. We restrict our attention to the spatio-temporal product density function......, and develop a non-parametric edge-corrected kernel estimate of the product density under the second-order intensity-reweighted stationary hypothesis. The expectation and variance of the estimator are obtained, and closed form expressions derived under the Poisson case. A detailed simulation study is presented...... to compare our close expression for the variance with estimated ones for Poisson cases. The simulation experiments show that the theoretical form for the variance gives acceptable values, which can be used in practice. Finally, we apply the resulting estimator to data on the spatio-temporal distribution...

Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity

Science.gov (United States)

Marks, Michael; Kroupa, Pavel; Dabringhausen, Jörg; Pawlowski, Marcel S.

2012-05-01

Residual-gas expulsion after cluster formation has recently been shown to leave an imprint in the low-mass present-day stellar mass function (PDMF) which allowed the estimation of birth conditions of some Galactic globular clusters (GCs) such as mass, radius and star formation efficiency. We show that in order to explain their characteristics (masses, radii, metallicity and PDMF) their stellar initial mass function (IMF) must have been top heavy. It is found that the IMF is required to become more top heavy the lower the cluster metallicity and the larger the pre-GC cloud-core density are. The deduced trends are in qualitative agreement with theoretical expectation. The results are consistent with estimates of the shape of the high-mass end of the IMF in the Arches cluster, Westerlund 1, R136 and NGC 3603, as well as with the IMF independently constrained for ultra-compact dwarf galaxies (UCDs). The latter suggests that GCs and UCDs might have formed along the same channel or that UCDs formed via mergers of GCs. A Fundamental Plane is found which describes the variation of the IMF with density and metallicity of the pre-GC cloud cores. The implications for the evolution of galaxies and chemical enrichment over cosmological times are expected to be major.

Density functional study of the group II phosphide semiconductor compounds under hydrostatic pressure

Energy Technology Data Exchange (ETDEWEB)

Mokhtari, Ali [Simulation Laboratory, Department of Physics, Faculty of Science, Shahrekord University, PB 115, Shahrekord (Iran, Islamic Republic of)], E-mail: mokhtari@sci.sku.ac.ir

2008-04-02

The full-potential all-electron linearized augmented plane wave plus local orbital (FP-LAPW+lo) method, as implemented in the suite of software WIEN2k, has been used to systematically investigate the structural and electronic properties of the group II phosphide semiconductor compounds M{sub 3}P{sub 2} (M = Be, Mg and Ca). The exchange-correlation functional was approximated as a generalized gradient functional introduced by Perdew-Burke-Ernzerhof (GGA96) and Engel-Vosko (EV-GGA). Internal parameters were optimized by relaxing the atomic positions in the force directions using the Hellman-Feynman approach. The structural parameters, bulk modules, cohesive energy, band structures and density of states have been calculated and compared to the available experimental and theoretical results. These compounds are predicted to be semiconductors with the direct band gap of about 1.60, 2.55 and 2.62 eV for Be{sub 3}P{sub 2}, Mg{sub 3}P{sub 2} and Ca{sub 3}P{sub 2}, respectively. The effects of hydrostatic pressure on the behavior of band parameters such as band gap, valence bandwidths and anti-symmetric gap (the energy gap between two parts of the valence bands) are investigated using both GGA96 and EV-GGA. The contribution of s, p and d orbitals of different atoms to the density of states is discussed in detail.

Density functional study of the group II phosphide semiconductor compounds under hydrostatic pressure

International Nuclear Information System (INIS)

Mokhtari, Ali

2008-01-01

The full-potential all-electron linearized augmented plane wave plus local orbital (FP-LAPW+lo) method, as implemented in the suite of software WIEN2k, has been used to systematically investigate the structural and electronic properties of the group II phosphide semiconductor compounds M 3 P 2 (M = Be, Mg and Ca). The exchange-correlation functional was approximated as a generalized gradient functional introduced by Perdew-Burke-Ernzerhof (GGA96) and Engel-Vosko (EV-GGA). Internal parameters were optimized by relaxing the atomic positions in the force directions using the Hellman-Feynman approach. The structural parameters, bulk modules, cohesive energy, band structures and density of states have been calculated and compared to the available experimental and theoretical results. These compounds are predicted to be semiconductors with the direct band gap of about 1.60, 2.55 and 2.62 eV for Be 3 P 2 , Mg 3 P 2 and Ca 3 P 2 , respectively. The effects of hydrostatic pressure on the behavior of band parameters such as band gap, valence bandwidths and anti-symmetric gap (the energy gap between two parts of the valence bands) are investigated using both GGA96 and EV-GGA. The contribution of s, p and d orbitals of different atoms to the density of states is discussed in detail

Improved density functional calculations for atoms, molecules and surfaces

International Nuclear Information System (INIS)

Fricke, B.; Anton, J.; Fritzsche, S.; Sarpe-Tudoran, C.

2005-01-01

The non-collinear and collinear descriptions within relativistic density functional theory is described. We present results of both non-collinear and collinear calculations for atoms, diatomic molecules, and some surface simulations. We find that the accuracy of our density functional calculations for the smaller systems is comparable to good quantum chemical calculations, and thus this method provides a sound basis for larger systems where no such comparison is possible. (author)

Comparison of density functional and modified Poisson-Boltzmann structural properties for a spherical double layer

Directory of Open Access Journals (Sweden)

L.B.Bhuiyan

2005-01-01

Full Text Available The density functional and modified Poisson-Boltzmann descriptions of a spherical (electric double layer are compared and contrasted vis-a-vis existing Monte Carlo simulation data (for small ion diameter 4.25·10-10 m from the literature for a range of physical parameters such as macroion surface charge, macroion radius, valencies of the small ions, and electrolyte concentration. Overall, the theoretical predictions are seen to be remarkably consistent between themselves, being also in very good agreement with the simulations. Some modified Poisson-Boltzmann results for the zeta potential at small ion diameters of 3 and 2·10-10 m are also reported.

The hydrogen bond in ice probed by soft x-ray spectroscopy and density functional theory

International Nuclear Information System (INIS)

Nilsson, A.; Ogasawara, H.; Cavalleri, M.; Nordlund, D.; Nyberg, M.; Wernet, Ph.; Pettersson, L.G.M.

2005-01-01

We combine photoelectron and x-ray absorption spectroscopy with density functional theory to derive a molecular orbital picture of the hydrogen bond in ice. We find that the hydrogen bond involves donation and back-donation of charge between the oxygen lone pair and the O-H antibonding orbitals on neighboring molecules. Together with internal s-p rehybridization this minimizes the repulsive charge overlap of the connecting oxygen and hydrogen atoms, which is essential for a strong attractive electrostatic interaction. Our joint experimental and theoretical results demonstrate that an electrostatic model based on only charge induction from the surrounding medium fails to properly describe the internal charge redistributions upon hydrogen bonding

Relativistic density functional theory with picture-change corrected electron density based on infinite-order Douglas-Kroll-Hess method

Science.gov (United States)

Oyama, Takuro; Ikabata, Yasuhiro; Seino, Junji; Nakai, Hiromi

2017-07-01

This Letter proposes a density functional treatment based on the two-component relativistic scheme at the infinite-order Douglas-Kroll-Hess (IODKH) level. The exchange-correlation energy and potential are calculated using the electron density based on the picture-change corrected density operator transformed by the IODKH method. Numerical assessments indicated that the picture-change uncorrected density functional terms generate significant errors, on the order of hartree for heavy atoms. The present scheme was found to reproduce the energetics in the four-component treatment with high accuracy.

Time-dependent quantum fluid density functional theory of hydrogen ...

Indian Academy of Sciences (India)

WINTEC

density functional theory; quantum fluid dynamics. 1. Introduction ... dynamics of strongly non-linear interaction of atoms with intense ... theory and quantum fluid dynamics in real space. .... clear evidence of bond softening since density in the.

Application of RBF neural network improved by peak density function in intelligent color matching of wood dyeing

International Nuclear Information System (INIS)

Guan, Xuemei; Zhu, Yuren; Song, Wenlong

2016-01-01

According to the characteristics of wood dyeing, we propose a predictive model of pigment formula for wood dyeing based on Radial Basis Function (RBF) neural network. In practical application, however, it is found that the number of neurons in the hidden layer of RBF neural network is difficult to determine. In general, we need to test several times according to experience and prior knowledge, which is lack of a strict design procedure on theoretical basis. And we also don’t know whether the RBF neural network is convergent. This paper proposes a peak density function to determine the number of neurons in the hidden layer. In contrast to existing approaches, the centers and the widths of the radial basis function are initialized by extracting the features of samples. So the uncertainty caused by random number when initializing the training parameters and the topology of RBF neural network is eliminated. The average relative error of the original RBF neural network is 1.55% in 158 epochs. However, the average relative error of the RBF neural network which is improved by peak density function is only 0.62% in 50 epochs. Therefore, the convergence rate and approximation precision of the RBF neural network are improved significantly.

Central depression in nucleonic densities: Trend analysis in the nuclear density functional theory approach

Science.gov (United States)

Schuetrumpf, B.; Nazarewicz, W.; Reinhard, P.-G.

2017-08-01

Background: The central depression of nucleonic density, i.e., a reduction of density in the nuclear interior, has been attributed to many factors. For instance, bubble structures in superheavy nuclei are believed to be due to the electrostatic repulsion. In light nuclei, the mechanism behind the density reduction in the interior has been discussed in terms of shell effects associated with occupations of s orbits. Purpose: The main objective of this work is to reveal mechanisms behind the formation of central depression in nucleonic densities in light and heavy nuclei. To this end, we introduce several measures of the internal nucleonic density. Through the statistical analysis, we study the information content of these measures with respect to nuclear matter properties. Method: We apply nuclear density functional theory with Skyrme functionals. Using the statistical tools of linear least square regression, we inspect correlations between various measures of central depression and model parameters, including nuclear matter properties. We study bivariate correlations with selected quantities as well as multiple correlations with groups of parameters. Detailed correlation analysis is carried out for 34Si for which a bubble structure has been reported recently, 48Ca, and N =82 , 126, and 184 isotonic chains. Results: We show that the central depression in medium-mass nuclei is very sensitive to shell effects, whereas for superheavy systems it is firmly driven by the electrostatic repulsion. An appreciable semibubble structure in proton density is predicted for 294Og, which is currently the heaviest nucleus known experimentally. Conclusion: Our correlation analysis reveals that the central density indicators in nuclei below 208Pb carry little information on parameters of nuclear matter; they are predominantly driven by shell structure. On the other hand, in the superheavy nuclei there exists a clear relationship between the central nucleonic density and symmetry energy.

The maximal-density mass function for primordial black hole dark matter

Science.gov (United States)

Lehmann, Benjamin V.; Profumo, Stefano; Yant, Jackson

2018-04-01

The advent of gravitational wave astronomy has rekindled interest in primordial black holes (PBH) as a dark matter candidate. As there are many different observational probes of the PBH density across different masses, constraints on PBH models are dependent on the functional form of the PBH mass function. This complicates general statements about the mass functions allowed by current data, and, in particular, about the maximum total density of PBH. Numerical studies suggest that some forms of extended mass functions face tighter constraints than monochromatic mass functions, but they do not preclude the existence of a functional form for which constraints are relaxed. We use analytical arguments to show that the mass function which maximizes the fraction of the matter density in PBH subject to all constraints is a finite linear combination of monochromatic mass functions. We explicitly compute the maximum fraction of dark matter in PBH for different combinations of current constraints, allowing for total freedom of the mass function. Our framework elucidates the dependence of the maximum PBH density on the form of observational constraints, and we discuss the implications of current and future constraints for the viability of the PBH dark matter paradigm.

Experimental and theoretical investigation of the effect of SiO2 content in gate dielectrics on work function shift induced by nanoscale capping layers

KAUST Repository

Caraveo-Frescas, J. A.; Wang, H.; Schwingenschlö gl, Udo; Alshareef, Husam N.

2012-01-01

The impact of SiO2 content in ultrathin gate dielectrics on the magnitude of the effective work function (EWF) shift induced by nanoscale capping layers has been investigated experimentally and theoretically. The magnitude of the effective work function shift for four different capping layers (AlN, Al2O3, La2O3, and Gd2O3) is measured as a function of SiO2 content in the gate dielectric. A nearly linear increase of this shift with SiO2 content is observed for all capping layers. The origin of this dependence is explained using density functional theory simulations.

Experimental and theoretical investigation of the effect of SiO2 content in gate dielectrics on work function shift induced by nanoscale capping layers

KAUST Repository

Caraveo-Frescas, J. A.

2012-09-10

The impact of SiO2 content in ultrathin gate dielectrics on the magnitude of the effective work function (EWF) shift induced by nanoscale capping layers has been investigated experimentally and theoretically. The magnitude of the effective work function shift for four different capping layers (AlN, Al2O3, La2O3, and Gd2O3) is measured as a function of SiO2 content in the gate dielectric. A nearly linear increase of this shift with SiO2 content is observed for all capping layers. The origin of this dependence is explained using density functional theory simulations.

Theoretical prediction of low-density hexagonal ZnO hollow structures

Energy Technology Data Exchange (ETDEWEB)

Tuoc, Vu Ngoc, E-mail: tuoc.vungoc@hust.edu.vn [Institute of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi (Viet Nam); Huan, Tran Doan [Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Thao, Nguyen Thi [Institute of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi (Viet Nam); Hong Duc University, 307 Le Lai, Thanh Hoa City (Viet Nam); Tuan, Le Manh [Hong Duc University, 307 Le Lai, Thanh Hoa City (Viet Nam)

2016-10-14

Along with wurtzite and zinc blende, zinc oxide (ZnO) has been found in a large number of polymorphs with substantially different properties and, hence, applications. Therefore, predicting and synthesizing new classes of ZnO polymorphs are of great significance and have been gaining considerable interest. Herein, we perform a density functional theory based tight-binding study, predicting several new series of ZnO hollow structures using the bottom-up approach. The geometry of the building blocks allows for obtaining a variety of hexagonal, low-density nanoporous, and flexible ZnO hollow structures. Their stability is discussed by means of the free energy computed within the lattice-dynamics approach. Our calculations also indicate that all the reported hollow structures are wide band gap semiconductors in the same fashion with bulk ZnO. The electronic band structures of the ZnO hollow structures are finally examined in detail.

Benchmarks for electronically excited states: Time-dependent density functional theory and density functional theory based multireference configuration interaction

DEFF Research Database (Denmark)

Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.

2008-01-01

Time-dependent density functional theory (TD-DFT) and DFT-based multireference configuration interaction (DFT/MRCI) calculations are reported for a recently proposed benchmark set of 28 medium-sized organic molecules. Vertical excitation energies, oscillator strengths, and excited-state dipole...

Balancing Exchange Mixing in Density-Functional Approximations for Iron Porphyrin.

Science.gov (United States)

Berryman, Victoria E J; Boyd, Russell J; Johnson, Erin R

2015-07-14

Predicting the correct ground-state multiplicity for iron(II) porphyrin, a high-spin quintet, remains a significant challenge for electronic-structure methods, including commonly employed density functionals. An even greater challenge for these methods is correctly predicting favorable binding of O2 to iron(II) porphyrin, due to the open-shell singlet character of the adduct. In this work, the performance of a modest set of contemporary density-functional approximations is assessed and the results interpreted using Bader delocalization indices. It is found that inclusion of greater proportions of Hartree-Fock exchange, in hybrid or range-separated hybrid functionals, has opposing effects; it improves the ability of the functional to identify the ground state but is detrimental to predicting favorable dioxygen binding. Because of the uncomplementary nature of these properties, accurate prediction of both the relative spin-state energies and the O2 binding enthalpy eludes conventional density-functional approximations.

Efficient estimation of dynamic density functions with an application to outlier detection

KAUST Repository

Qahtan, Abdulhakim Ali Ali; Zhang, Xiangliang; Wang, Suojin

2012-01-01

In this paper, we propose a new method to estimate the dynamic density over data streams, named KDE-Track as it is based on a conventional and widely used Kernel Density Estimation (KDE) method. KDE-Track can efficiently estimate the density with linear complexity by using interpolation on a kernel model, which is incrementally updated upon the arrival of streaming data. Both theoretical analysis and experimental validation show that KDE-Track outperforms traditional KDE and a baseline method Cluster-Kernels on estimation accuracy of the complex density structures in data streams, computing time and memory usage. KDE-Track is also demonstrated on timely catching the dynamic density of synthetic and real-world data. In addition, KDE-Track is used to accurately detect outliers in sensor data and compared with two existing methods developed for detecting outliers and cleaning sensor data. © 2012 ACM.

Periodic Density Functional Theory Study of the Structure, Raman Spectrum, and Mechanical Properties of Schoepite Mineral.

Science.gov (United States)

Colmenero, Francisco; Cobos, Joaquín; Timón, Vicente

2018-04-16

The structure and Raman spectrum of schoepite mineral, [(UO 2 ) 8 O 2 (OH) 12 ]·12H 2 O, was studied by means of theoretical calculations. The computations were carried out by using density functional theory with plane waves and pseudopotentials. A norm-conserving pseudopotential specific for the U atom developed in a previous work was employed. Because it was not possible to locate H atoms directly from X-ray diffraction (XRD) data by structure refinement in previous experimental studies, all of the positions of the H atoms in the full unit cell were determined theoretically. The structural results, including the lattice parameters, bond lengths, bond angles, and powder XRD pattern, were found to be in good agreement with their experimental counterparts. However, the calculations performed using the unit cell designed by Ostanin and Zeller in 2007, involving half of the atoms of the full unit cell, led to significant errors in the computed powder XRD pattern. Furthermore, Ostanin and Zeller's unit cell contains hydronium ions, H 3 O + , which are incompatible with the experimental information. Therefore, while the use of this schoepite model may be a very useful approximation requiring a much smaller amount of computational effort, the full unit cell should be used to study this mineral accurately. The Raman spectrum was also computed by means of density functional perturbation theory and compared with the experimental spectrum. The results were also in agreement with the experimental data. A normal-mode analysis of the theoretical spectra was performed to assign the main bands of the Raman spectrum. This assignment significantly improved the current empirical assignment of the bands of the Raman spectrum of schoepite mineral. In addition, the equation of state and elastic properties of this mineral were determined. The crystal structure of schoepite was found to be stable mechanically and dynamically. Schoepite can be described as a brittle material exhibiting

Information-theoretic lengths of Jacobi polynomials

Energy Technology Data Exchange (ETDEWEB)

Guerrero, A; Dehesa, J S [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad de Granada, Granada (Spain); Sanchez-Moreno, P, E-mail: agmartinez@ugr.e, E-mail: pablos@ugr.e, E-mail: dehesa@ugr.e [Instituto ' Carlos I' de Fisica Teorica y Computacional, Universidad de Granada, Granada (Spain)

2010-07-30

The information-theoretic lengths of the Jacobi polynomials P{sup ({alpha}, {beta})}{sub n}(x), which are information-theoretic measures (Renyi, Shannon and Fisher) of their associated Rakhmanov probability density, are investigated. They quantify the spreading of the polynomials along the orthogonality interval [- 1, 1] in a complementary but different way as the root-mean-square or standard deviation because, contrary to this measure, they do not refer to any specific point of the interval. The explicit expressions of the Fisher length are given. The Renyi lengths are found by the use of the combinatorial multivariable Bell polynomials in terms of the polynomial degree n and the parameters ({alpha}, {beta}). The Shannon length, which cannot be exactly calculated because of its logarithmic functional form, is bounded from below by using sharp upper bounds to general densities on [- 1, +1] given in terms of various expectation values; moreover, its asymptotics is also pointed out. Finally, several computational issues relative to these three quantities are carefully analyzed.

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

Approach to kinetic energy density functionals: Nonlocal terms with the structure of the von Weizsaecker functional

International Nuclear Information System (INIS)

Garcia-Aldea, David; Alvarellos, J. E.

2008-01-01

We propose a kinetic energy density functional scheme with nonlocal terms based on the von Weizsaecker functional, instead of the more traditional approach where the nonlocal terms have the structure of the Thomas-Fermi functional. The proposed functionals recover the exact kinetic energy and reproduce the linear response function of homogeneous electron systems. In order to assess their quality, we have tested the total kinetic energies as well as the kinetic energy density for atoms. The results show that these nonlocal functionals give as good results as the most sophisticated functionals in the literature. The proposed scheme for constructing the functionals means a step ahead in the field of fully nonlocal kinetic energy functionals, because they are capable of giving better local behavior than the semilocal functionals, yielding at the same time accurate results for total kinetic energies. Moreover, the functionals enjoy the possibility of being evaluated as a single integral in momentum space if an adequate reference density is defined, and then quasilinear scaling for the computational cost can be achieved

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.

Capillary wave Hamiltonian for the Landau–Ginzburg–Wilson density functional

International Nuclear Information System (INIS)

Chacón, Enrique; Tarazona, Pedro

2016-01-01

We study the link between the density functional (DF) formalism and the capillary wave theory (CWT) for liquid surfaces, focused on the Landau–Ginzburg–Wilson (LGW) model, or square gradient DF expansion, with a symmetric double parabola free energy, which has been extensively used in theoretical studies of this problem. We show the equivalence between the non-local DF results of Parry and coworkers and the direct evaluation of the mean square fluctuations of the intrinsic surface, as is done in the intrinsic sampling method for computer simulations. The definition of effective wave-vector dependent surface tensions is reviewed and we obtain new proposals for the LGW model. The surface weight proposed by Blokhuis and the surface mode analysis proposed by Stecki provide consistent and optimal effective definitions for the extended CWT Hamiltonian associated to the DF model. A non-local, or coarse-grained, definition of the intrinsic surface provides the missing element to get the mesoscopic surface Hamiltonian from the molecular DF description, as had been proposed a long time ago by Dietrich and coworkers. (paper)

Density and mechanical properties of calcium aluminate cement

Science.gov (United States)

Ahmed, Syed Taqi Uddin; Ahmmad, Shaik Kareem

2018-04-01

Calcium aluminate cements are a special type of cements which have their composition mainly dominated by the presence of Monocalcium Aluminates. In the present paper for the first time we have shown theoretical density and elastic constants for various calcium aluminate cements. The density of the present CAS decrease with aluminates presents in the cement. Using the density data, the elastic moduli namely Young's modulus, bulk and shear modulus show strong linear dependence as a function of compositional parameter.

PREFACE: Classical density functional theory methods in soft and hard matter Classical density functional theory methods in soft and hard matter

Science.gov (United States)

Haataja, Mikko; Gránásy, László; Löwen, Hartmut

2010-08-01

Herein we provide a brief summary of the background, events and results/outcome of the CECAM workshop 'Classical density functional theory methods in soft and hard matter held in Lausanne between October 21 and October 23 2009, which brought together two largely separately working communities, both of whom employ classical density functional techniques: the soft-matter community and the theoretical materials science community with interests in phase transformations and evolving microstructures in engineering materials. After outlining the motivation for the workshop, we first provide a brief overview of the articles submitted by the invited speakers for this special issue of Journal of Physics: Condensed Matter, followed by a collection of outstanding problems identified and discussed during the workshop. 1. Introduction Classical density functional theory (DFT) is a theoretical framework, which has been extensively employed in the past to study inhomogeneous complex fluids (CF) [1-4] and freezing transitions for simple fluids, amongst other things. Furthermore, classical DFT has been extended to include dynamics of the density field, thereby opening a new avenue to study phase transformation kinetics in colloidal systems via dynamical DFT (DDFT) [5]. While DDFT is highly accurate, the computations are numerically rather demanding, and cannot easily access the mesoscopic temporal and spatial scales where diffusional instabilities lead to complex solidification morphologies. Adaptation of more efficient numerical methods would extend the domain of DDFT towards this regime of particular interest to materials scientists. In recent years, DFT has re-emerged in the form of the so-called 'phase-field crystal' (PFC) method for solid-state systems [6, 7], and it has been successfully employed to study a broad variety of interesting materials phenomena in both atomic and colloidal systems, including elastic and plastic deformations, grain growth, thin film growth, solid

Blue functions: probability and current density propagators in non-relativistic quantum mechanics

International Nuclear Information System (INIS)

Withers, L P Jr

2011-01-01

Like a Green function to propagate a particle's wavefunction in time, a Blue function is introduced to propagate the particle's probability and current density. Accordingly, the complete Blue function has four components. They are constructed from path integrals involving a quantity like the action that we call the motion. The Blue function acts on the displaced probability density as the kernel of an integral operator. As a result, we find that the Wigner density occurs as an expression for physical propagation. We also show that, in quantum mechanics, the displaced current density is conserved bilocally (in two places at one time), as expressed by a generalized continuity equation. (paper)

NATO Advanced Study Institute on Electron and Magnetization Densities in Molecules and Crystals

CERN Document Server

1980-01-01

The interest of describing the ground state properties of a system in terms of one electron density (or its two spin components) is obvious, in particular due to the simple physical significance of this function. Recent experimental progress in diffraction made the measurement of charge and magnetization densities in crystalline solids possible, with an accuracy at least as good as theoretical accuracy. Theoretical developments of the many-body problem have proved the extreme importance of the one electron density function and presently, accurate methods of band structure determination become available. Parallel to the diffraction techniques, other domains of research (inelastic scattering, resonance, molecular spectroscopy) deal with quantities directly related to the one particle density. But the two types of studies do not interfere enough and one should obviously gain more information by interpreting all experiments that are related to the density together. It became necessary to have an International Sch...

Synthesis, Crystal Structure, Density Function Theory, Molecular ...

African Journals Online (AJOL)

Tropical Journal of Pharmaceutical Research February 2016; 15 (2): 385-392 ... tested for its antimicrobial activities and computational studies including density function test (DFT) and docking ... agonists [4], selective dopamine D3 and D4 ...

An isomeric reaction benchmark set to test if the performance of state-of-the-art density functionals can be regarded as independent of the external potential.

Science.gov (United States)

Schwabe, Tobias

2014-07-28

Some representative density functionals are assessed for isomerization reactions in which heteroatoms are systematically substituted with heavier members of the same element group. By this, it is investigated if the functional performance depends on the elements involved, i.e. on the external potential imposed by the atomic nuclei. Special emphasis is placed on reliable theoretical reference data and the attempt to minimize basis set effects. Both issues are challenging for molecules including heavy elements. The data suggest that no general bias can be identified for the functionals under investigation except for one case - M11-L. Nevertheless, large deviations from the reference data can be found for all functional approximations in some cases. The average error range for the nine functionals in this test is 17.6 kcal mol(-1). These outliers depreciate the general reliability of density functional approximations.

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.

Spectroscopic and density functional theory studies of 5,7,3',5'-tetrahydroxyflavanone from the leaves of Olea ferruginea.

Science.gov (United States)

Hashmi, Muhammad Ali; Khan, Afsar; Ayub, Khurshid; Farooq, Umar

2014-07-15

5,7,3',5'-Tetrahydroxyflavanone (1) was isolated from the leaves of Olea ferruginea and a theoretical model was developed for obtaining the electronic and spectroscopic properties of 1. The geometric and electronic properties were calculated at B3LYP/6-311 G (d, p) level of Density Functional Theory (DFT). The theoretical data was in good agreement with the experimental one. The optimized geometric parameters of compound 1 were calculated for the first time. The theoretical vibrational frequencies of 1 were found to correlate with the experimental IR spectrum after a scaling factor of 0.9811. The UV and NMR spectral data computed theoretically were in good agreement with the experimental data. Electronic properties of the compound i.e., ionization potential (IP), electron affinity (EA), coefficients of HOMO and LUMO were estimated computationally for the first time which can be used to explain its antioxidant as well as other related activities and more active sites on it. The intermolecular interactions and their effects on IR frequencies, electronic and geometric parameters were simulated using water molecule as a model for hydrogen bonding with flavonoid hydroxyl groups. Copyright © 2014 Elsevier B.V. All rights reserved.

Comparative analysis of electron-density and electron-localization function for dinuclear manganese complexes with bridging boron- and carbon-centered ligands.

Science.gov (United States)

Götz, Kathrin; Kaupp, Martin; Braunschweig, Holger; Stalke, Dietmar

2009-01-01

Bonding in borylene-, carbene-, and vinylidene-bridged dinuclear manganese complexes [MnCp(CO)(2)](2)X (X = B-tBu, B = NMe(2), CH(2), C=CH(2)) has been compared by analyses based on quantum theory of atoms in molecules (QTAIM), on the electron-localization function (ELF), and by natural-population analyses. All of the density functional theory based analyses agree on the absence of a significant direct Mn-Mn bond in these complexes and confirm a dominance of delocalized bonding via the bridging ligand. Interestingly, however, the topology of both charge density and ELF related to the Mn-bridge-Mn bonding depend qualitatively on the chosen density functional (except for the methylene-bridged complex, which exhibits only one three-center-bonding attractor both in -nabla(2)rho and in ELF). While gradient-corrected functionals provide a picture with localized two-center X-Mn bonding, increasing exact-exchange admixture in hybrid functionals concentrates charge below the bridging atom and suggests a three-center bonding situation. For example, the bridging boron ligands may be described either as substituted boranes (e.g., at BLYP or BP86 levels) or as true bridging borylenes (e.g., at BHLYP level). This dependence on the theoretical level appears to derive from a bifurcation between two different bonding situations and is discussed in terms of charge transfer between X and Mn, and in the context of self-interaction errors exhibited by popular functionals.

Plato: A localised orbital based density functional theory code

Science.gov (United States)

Kenny, S. D.; Horsfield, A. P.

2009-12-01

The Plato package allows both orthogonal and non-orthogonal tight-binding as well as density functional theory (DFT) calculations to be performed within a single framework. The package also provides extensive tools for analysing the results of simulations as well as a number of tools for creating input files. The code is based upon the ideas first discussed in Sankey and Niklewski (1989) [1] with extensions to allow high-quality DFT calculations to be performed. DFT calculations can utilise either the local density approximation or the generalised gradient approximation. Basis sets from minimal basis through to ones containing multiple radial functions per angular momenta and polarisation functions can be used. Illustrations of how the package has been employed are given along with instructions for its utilisation. Program summaryProgram title: Plato Catalogue identifier: AEFC_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 219 974 No. of bytes in distributed program, including test data, etc.: 1 821 493 Distribution format: tar.gz Programming language: C/MPI and PERL Computer: Apple Macintosh, PC, Unix machines Operating system: Unix, Linux and Mac OS X Has the code been vectorised or parallelised?: Yes, up to 256 processors tested RAM: Up to 2 Gbytes per processor Classification: 7.3 External routines: LAPACK, BLAS and optionally ScaLAPACK, BLACS, PBLAS, FFTW Nature of problem: Density functional theory study of electronic structure and total energies of molecules, crystals and surfaces. Solution method: Localised orbital based density functional theory. Restrictions: Tight-binding and density functional theory only, no exact exchange. Unusual features: Both atom centred and uniform meshes available

Effect of the medium's density on the hydrocyclonic separation of waste plastics with different densities.

Science.gov (United States)

Fu, Shuangcheng; Fang, Yong; Yuan, Huixin; Tan, Wanjiang; Dong, Yiwen

2017-09-01

Hydrocyclones can be applied to recycle waste plastics with different densities through separating plastics based on their differences in densities. In the process, the medium density is one of key parameters and the value of the medium's density is not just the average of the density of two kinds of plastics separated. Based on the force analysis and establishing the equation of motion of particles in the hydrocyclone, a formula to calculate the optimum separation medium density has been deduced. This value of the medium's density is a function of various parameters including the diameter, density, radial position and tangential velocity of particles, and viscosity of the medium. Tests on the separation performance of the hydrocyclone has been conducted with PET and PVC particles. The theoretical result appeared to be in good agreement with experimental results. Copyright © 2017 Elsevier Ltd. All rights reserved.

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.

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.

Hydrogen atom addition to the surface of graphene nanoflakes: A density functional theory study

Energy Technology Data Exchange (ETDEWEB)

Tachikawa, Hiroto, E-mail: hiroto@eng.hokudai.ac.jp

2017-02-28

Highlights: • The reaction pathway of the hydrogen addition to graphene surface was determined by the DFT method. • Binding energies of atomic hydrogen to graphene surface were determined. • Absorption spectrum of hydrogenated graphene was theoretically predicted. • Hyperfine coupling constant of hydrogenated graphene was theoretically predicted. - Abstract: Polycyclic aromatic hydrocarbons (PAHs) provide a 2-dimensional (2D) reaction surface in 3-dimensional (3D) interstellar space and have been utilized as a model of graphene surfaces. In the present study, the reaction of PAHs with atomic hydrogen was investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of atomic hydrogen to graphene nanoflakes. PAHs with n = 4–37 were chosen, where n indicates the number of benzene rings. Activation energies of hydrogen addition to the graphene surface were calculated to be 5.2–7.0 kcal/mol at the CAM-B3LYP/6-311G(d,p) level, which is almost constant for all PAHs. The binding energies of hydrogen atom were slightly dependent on the size (n): 14.8–28.5 kcal/mol. The absorption spectra showed that a long tail is generated at the low-energy region after hydrogen addition to the graphene surface. The electronic states of hydrogenated graphenes were discussed on the basis of theoretical results.

Density functional study of gamma-aminopropyltriethoxysilane

International Nuclear Information System (INIS)

Bistricic, L; Volovsek, V; Daani, V; Leskovac, M

2006-01-01

Density functional theory calculations using Becke's three-parameter exchange functional in combination with the Lee-Young-Parr correlation functional (B3-LYP) and standard 6-311 + G(d,p) basis set were carried out to study the conformational stability and vibrational spectra of gamma-aminopropyltriethoxysilane. Calculations reveal the existence of two stable conformers trans and gauche. The calculated energy for the gauche conformation was found to be 608 cm -1 above the minimum energy of the trans conformation. Temperature dependence of Raman spectra of liquid APTES and DFT calculation enabled us to identify the vibrational bands characteristic for both conformers. It has been shown that there is an increase in the population of gauche conformer with increasing temperature

Hash functions and information theoretic security

DEFF Research Database (Denmark)

Bagheri, Nasoor; Knudsen, Lars Ramkilde; Naderi, Majid

2009-01-01

Information theoretic security is an important security notion in cryptography as it provides a true lower bound for attack complexities. However, in practice attacks often have a higher cost than the information theoretic bound. In this paper we study the relationship between information theoretic...

Ab initio and density functional theoretical design and screening of model crown ether based ligand (host) for extraction of lithium metal ion (guest): effect of donor and electronic induction.

Science.gov (United States)

Boda, Anil; Ali, Sk Musharaf; Rao, Hanmanth; Ghosh, Sandip K

2012-08-01

The structures, energetic and thermodynamic parameters of model crown ethers with different donor, cavity and electron donating/ withdrawing functional group have been determined with ab initio MP2 and density functional theory in gas and solvent phase. The calculated values of binding energy/ enthalpy for lithium ion complexation are marginally higher for hard donor based aza and oxa crown compared to soft donor based thia and phospha crown. The calculated values of binding enthalpy for lithium metal ion with 12C4 at MP2 level of theory is in good agreement with the available experimental result. The binding energy is altered due to the inductive effect imparted by the electron donating/ withdrawing group in crown ether, which is well correlated with the values of electron transfer. The role of entropy for extraction of hydrated lithium metal ion by different donor and functional group based ligand has been demonstrated. The HOMO-LUMO gap is decreased and dipole moment of the ligand is increased from gas phase to organic phase because of the dielectric constant of the solvent. The gas phase binding energy is reduced in solvent phase as the solvent molecules weaken the metal-ligand binding. The theoretical values of extraction energy for LiCl salt from aqueous solution in different organic solvent is validated by the experimental trend. The study presented here should contribute to the design of model host ligand and screening of solvent for metal ion recognition and thus can contribute in planning the experiments.

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

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.

Density Functional Theory and Materials Modeling at Atomistic Length Scales

Directory of Open Access Journals (Sweden)

Swapan K. Ghosh

2002-04-01

Full Text Available Abstract: We discuss the basic concepts of density functional theory (DFT as applied to materials modeling in the microscopic, mesoscopic and macroscopic length scales. The picture that emerges is that of a single unified framework for the study of both quantum and classical systems. While for quantum DFT, the central equation is a one-particle Schrodinger-like Kohn-Sham equation, the classical DFT consists of Boltzmann type distributions, both corresponding to a system of noninteracting particles in the field of a density-dependent effective potential, the exact functional form of which is unknown. One therefore approximates the exchange-correlation potential for quantum systems and the excess free energy density functional or the direct correlation functions for classical systems. Illustrative applications of quantum DFT to microscopic modeling of molecular interaction and that of classical DFT to a mesoscopic modeling of soft condensed matter systems are highlighted.

The molecular, electronic structures and vibrational spectra of metal-free, N,N'-dideuterio and magnesium tetra-2,3-pyridino-porphyrazines: Density functional calculations.

Science.gov (United States)

Liu, Zhongqiang; Zhang, Xianxi; Zhang, Yuexing; Li, Renjie; Jiang, Jianzhuang

2006-10-01

A theoretical investigation of the fully optimized geometries and electronic structures of the metal-free (TPdPzH(2)), N,N'-dideuterio (TPdPzD(2)), and magnesium (TPdPzMg) tetra-2,3-pyridino-porphyrazine has been conducted based on density functional theory. The optimized geometries at density functional theory level for these compounds are reported here for the first time. A comparison between the different molecules for the geometry, molecular orbital, and atomic charge is made. The substituent effect of the N atoms on the molecular structures of these compounds is discussed. The IR and Raman spectra for these three compounds have also been calculated at density functional B3LYP level using the 6-31G(d) basis set. Detailed assignments of the NH, NM, and pyridine ring vibrational bands in the IR and Raman spectra have been made based on assistance of animated pictures. The simulated IR spectra of TPdPzH(2) are compared with the experimental absorption spectra, and very good consistency has been found. The isotope effect on the IR and Raman spectra is also discussed.

Bone mineral density and menstrual function in adolescent female ...

African Journals Online (AJOL)

Bone mineral density and menstrual function in adolescent female long-distance runners - A prospective comparative study of bone structure and menstrual function in adolescent female endurance athletes from five secondary schools in Pretoria.

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.

VV and VO2 defects in silicon studied with hybrid density functional theory

KAUST Repository

Christopoulos, Stavros Richard G; Wang, Hao; Chroneos, Alexander I.; Londos, Charalampos A.; Sgourou, Efstratia N.; Schwingenschlö gl, Udo

2014-01-01

The formation of VO (A-center), VV and VO2 defects in irradiated Czochralski-grown silicon (Si) is of technological importance. Recent theoretical studies have examined the formation and charge states of the A-center in detail. Here we use density

Performance of Several Density Functional Theory Methods on Describing Hydrogen-Bond Interactions.

Science.gov (United States)

Rao, Li; Ke, Hongwei; Fu, Gang; Xu, Xin; Yan, Yijing

2009-01-13

We have investigated eleven density functionals, including LDA, PBE, mPWPW91, TPSS, B3LYP, X3LYP, PBE0, O3LYP, B97-1, MPW1K, and TPSSh, for their performances on describing hydrogen bond (HB) interactions. The emphasis has been laid not only on their abilities to calculate the intermolecular hydrogen bonding energies but also on their performances in predicting the relative energies of intermolecular H-bonded complexes and the conformer stabilities due to intramolecular hydrogen bondings. As compared to the best theoretical values, we found that although PBE and PBE0 gave the best estimation of HB strengths, they might fail to predict the correct order of relative HB energies, which might lead to a wrong prediction of the global minimum for different conformers. TPSS and TPSSh did not always improve over PBE and PBE0. B3LYP was found to underestimate the intermolecular HB strengths but was among the best performers in calculating the relative HB energies. We showed here that X3LYP and B97-1 were able to give good values for both absolute HB strengths and relative HB energies, making these functionals good candidates for HB description.

Application of gradient-corrected density functional theory to the structures and thermochemistries of ScF3, TiF4, VF5, and CrF6

International Nuclear Information System (INIS)

Russo, T.V.; Martin, R.L.; Jeffrey Hay, P.

1995-01-01

Density functional theory (DFT) and Hartree--Fock (HF) calculations are reported for the family of transition metal fluorides ScF 3 , TiF 4 , VF 5 , and CrF 6 . Both HF and the local-density approximation (LDA) yield excellent agreement with experimental bond lengths, while the B-LYP gradient-corrected density functional gives bond lengths 0.04-0.05 A too long. An investigation of various combinations of exchange and correlation functionals shows that, for this series, the origin of this behavior lies in the Becke exchange functional. Much improved bond distances are found using the hybrid HF/DFT functional advocated by Becke. This approximation also leads to much improved thermochemistries. The LDA overestimates average bond energies in this series by 30-40 kcal/mol, whereas the B-LYP functional overbinds by only ∼8-12 kcal/mol, and the hybrid HF/DFT method overbinds by only ∼2 kcal/mol. The hybrid method predicts the octahedral isomer of CrF 6 to be more stable than the trigonal prismatic form by 14 kcal/mol. Comparison of theoretical vibrational frequencies with experiment supports the assignment of an octahedral geometry

Response functions of cold neutron matter: density, spin and current fluctuations

Energy Technology Data Exchange (ETDEWEB)

Keller, Jochen; Sedrakian, Armen [Institut fuer Theoretische Physik, Goethe-Universitaet, Frankfurt am Main (Germany)

2014-07-01

We study the response of a single-component pair-correlated baryonic Fermi-liquid to density, spin, and their current perturbations. A complete set of response functions is calculated in the low-temperature regime. We derive the spectral functions of collective excitations associated with the density, density-current, spin, and spin-current perturbations. The dispersion relations of density and spin fluctuations are determined and it is shown that the density fluctuations lead to exciton-like undamped bound states, whereas the spin excitations correspond to diffusive modes above the pair-breaking threshold. The contribution of the collective pair-breaking modes to the specific heat of neutron matter at subnuclear densities is computed and is shown to be comparable to that of the degenerate electron gas at not too low temperatures.

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.

Nonlocal and Nonadiabatic Effects in the Charge-Density Response of Solids: A Time-Dependent Density-Functional Approach

Science.gov (United States)

Panholzer, Martin; Gatti, Matteo; Reining, Lucia

2018-04-01

The charge-density response of extended materials is usually dominated by the collective oscillation of electrons, the plasmons. Beyond this feature, however, intriguing many-body effects are observed. They cannot be described by one of the most widely used approaches for the calculation of dielectric functions, which is time-dependent density functional theory (TDDFT) in the adiabatic local density approximation (ALDA). Here, we propose an approximation to the TDDFT exchange-correlation kernel which is nonadiabatic and nonlocal. It is extracted from correlated calculations in the homogeneous electron gas, where we have tabulated it for a wide range of wave vectors and frequencies. A simple mean density approximation allows one to use it in inhomogeneous materials where the density varies on a scale of 1.6 rs or faster. This kernel contains effects that are completely absent in the ALDA; in particular, it correctly describes the double plasmon in the dynamic structure factor of sodium, and it shows the characteristic low-energy peak that appears in systems with low electronic density. It also leads to an overall quantitative improvement of spectra.

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory

International Nuclear Information System (INIS)

Zuniga-Gutierrez, Bernardo; Camacho-Gonzalez, Monica; Bendana-Castillo, Alfonso; Simon-Bastida, Patricia; Calaminici, Patrizia; Köster, Andreas M.

2015-01-01

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H 12 C– 12 CH–DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory

Energy Technology Data Exchange (ETDEWEB)

Zuniga-Gutierrez, Bernardo, E-mail: bzuniga.51@gmail.com [Departamento de Ciencias Computacionales, Universidad de Guadalajara, Blvd. Marcelino García Barragán 1421, C.P. 44430 Guadalajara, Jalisco (Mexico); Camacho-Gonzalez, Monica [Universidad Tecnológica de Tecámac, División A2, Procesos Industriales, Carretera Federal México Pachuca Km 37.5, Col. Sierra Hermosa, C.P. 55740 Tecámac, Estado de México (Mexico); Bendana-Castillo, Alfonso [Universidad Tecnológica de Tecámac, División A3, Tecnologías de la Información y Comunicaciones, Carretera Federal México Pachuca Km 37.5, Col. Sierra Hermosa, C.P. 55740 Tecámac, Estado de México (Mexico); Simon-Bastida, Patricia [Universidad Tecnlógica de Tulancingo, División Electromecánica, Camino a Ahuehuetitla No. 301, Col. Las Presas, C.P. 43642 Tulancingo, Hidalgo (Mexico); Calaminici, Patrizia; Köster, Andreas M. [Departamento de Química, CINVESTAV, Avenida Instituto Politécnico Nacional 2508, A.P. 14-740, México D.F. 07000 (Mexico)

2015-09-14

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H{sup 12}C–{sup 12}CH–DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory.

Science.gov (United States)

Zuniga-Gutierrez, Bernardo; Camacho-Gonzalez, Monica; Bendana-Castillo, Alfonso; Simon-Bastida, Patricia; Calaminici, Patrizia; Köster, Andreas M

2015-09-14

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H(12)C-(12)CH-DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.

Allometric scaling of population variance with mean body size is predicted from Taylor's law and density-mass allometry.

Science.gov (United States)

Cohen, Joel E; Xu, Meng; Schuster, William S F

2012-09-25

Two widely tested empirical patterns in ecology are combined here to predict how the variation of population density relates to the average body size of organisms. Taylor's law (TL) asserts that the variance of the population density of a set of populations is a power-law function of the mean population density. Density-mass allometry (DMA) asserts that the mean population density of a set of populations is a power-law function of the mean individual body mass. Combined, DMA and TL predict that the variance of the population density is a power-law function of mean individual body mass. We call this relationship "variance-mass allometry" (VMA). We confirmed the theoretically predicted power-law form and the theoretically predicted parameters of VMA, using detailed data on individual oak trees (Quercus spp.) of Black Rock Forest, Cornwall, New York. These results connect the variability of population density to the mean body mass of individuals.

A Comparative Density Functional Theory and Density Functional Tight Binding Study of Phases of Nitrogen Including a High Energy Density Material N8

Directory of Open Access Journals (Sweden)

Nicholas Capel

2015-11-01

Full Text Available We present a comparative dispersion-corrected Density Functional Theory (DFT and Density Functional Tight Binding (DFTB-D study of several phases of nitrogen, including the well-known alpha, beta, and gamma phases as well as recently discovered highly energetic phases: covalently bound cubic gauche (cg nitrogen and molecular (vdW-bound N8 crystals. Among several tested parametrizations of N–N interactions for DFTB, we identify only one that is suitable for modeling of all these phases. This work therefore establishes the applicability of DFTB-D to studies of phases, including highly metastable phases, of nitrogen, which will be of great use for modelling of dynamics of reactions involving these phases, which may not be practical with DFT due to large required space and time scales. We also derive a dispersion-corrected DFT (DFT-D setup (atom-centered basis parameters and Grimme dispersion parameters tuned for accurate description simultaneously of several nitrogen allotropes including covalently and vdW-bound crystals and including high-energy phases.

The use of perturbation theory in density-functional theory

International Nuclear Information System (INIS)

Goerling, A.

1996-01-01

Perturbation theory with respect to the electron-electron interaction leads to expressions for the exchange and correlation energies and potentials in terms of Kohn-Sham orbitals and Kohn-Sham eigenvalues. An exact open-quote exchange-only close-quote procedure for solids is introduced. Results for several semiconductors are presented. Perturbation theory expansions for the hardness of molecules and the bad gap of solids are given. Density-functional exchange and correlation energies for excited states are defined and a perturbation theory based Kohn-Sham formalism to treat excited states within density-functional theory is introduced

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.

Density functional theory calculations of charge transport properties ...

Indian Academy of Sciences (India)

ZIRAN CHEN

2017-08-04

Aug 4, 2017 ... properties of 'plate-like' coronene topological structures ... Keywords. Organic semiconductors; density functional theory; charge carrier mobility; ambipolar transport; ..... nology Department of Sichuan Province (Grant Number.

Towards improved local hybrid functionals by calibration of exchange-energy densities

International Nuclear Information System (INIS)

Arbuznikov, Alexei V.; Kaupp, Martin

2014-01-01

A new approach for the calibration of (semi-)local and exact exchange-energy densities in the context of local hybrid functionals is reported. The calibration functions are derived from only the electron density and its spatial derivatives, avoiding spatial derivatives of the exact-exchange energy density or other computationally unfavorable contributions. The calibration functions fulfill the seven more important out of nine known exact constraints. It is shown that calibration improves substantially the definition of a non-dynamical correlation energy term for generalized gradient approximation (GGA)-based local hybrids. Moreover, gauge artifacts in the potential-energy curves of noble-gas dimers may be corrected by calibration. The developed calibration functions are then evaluated for a large range of energy-related properties (atomization energies, reaction barriers, ionization potentials, electron affinities, and total atomic energies) of three sets of local hybrids, using a simple one-parameter local-mixing. The functionals are based on (a) local spin-density approximation (LSDA) or (b) Perdew-Burke-Ernzerhof (PBE) exchange and correlation, and on (c) Becke-88 (B88) exchange and Lee-Yang-Parr (LYP) correlation. While the uncalibrated GGA-based functionals usually provide very poor thermochemical data, calibration allows a dramatic improvement, accompanied by only a small deterioration of reaction barriers. In particular, an optimized BLYP-based local-hybrid functional has been found that is a substantial improvement over the underlying global hybrids, as well as over previously reported LSDA-based local hybrids. It is expected that the present calibration approach will pave the way towards new generations of more accurate hyper-GGA functionals based on a local mixing of exchange-energy densities

Density-dependent phonoriton states in highly excited semiconductors

International Nuclear Information System (INIS)

Nguyen Hong Quang; Nguyen Minh Khue; Nguyen Que Huong

1995-09-01

The dynamical aspects of the phonoriton state in highly-photoexcited semiconductors is studied theoretically. The effect of the exciton-exciton interaction and nonbosonic character of high-density excitons are taken into account. Using Green's function method and within the Random Phase Approximation it is shown that the phonoriton dispersion and damping are very sensitive to the exciton density, characterizing the excitation degree of semiconductors. (author). 18 refs, 3 figs

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

Surface chemistry and density distribution influence on visible luminescence of silicon quantum dots: an experimental and theoretical approach.

Science.gov (United States)

Dutt, Ateet; Matsumoto, Yasuhiro; Santana-Rodríguez, G; Ramos, Estrella; Monroy, B Marel; Santoyo Salazar, J

2017-01-04

The impact of the surface reconstruction of the density distribution and photoluminescence of silicon quantum dots (QDs) embedded in a silicon oxide matrix (SiO x ) has been studied. Annealing treatments carried out on the as-deposited samples provoked the effusion of hydrogen species. Moreover, depending on the surrounding density and coalescence of QDs, they resulted in a change in the average size of the particles depending on the initial local environment. The shift in the luminescence spectra all over the visible region (blue, green and red) shows a strong dependence on the resultant change in the size and/or the passivation environment of QDs. Density functional theoretical (DFT) calculations support this fact and explain the possible electronic transitions (HOMO-LUMO gap) involved. Passivation in the presence of oxygen species lowers the band gap of Si 29 and Si 35 nanoclusters up to 1.7 eV, whereas, surface passivation in the environment of hydrogen species increases the band gap up to 4.4 eV. These results show a good agreement with the quantum confinement model described in this work and explain the shift in the luminescence all over the visible region. The results reported here offer vital insight into the mechanism of emission from silicon quantum dots which has been one of the most debated topics in the last two decades. QDs with multiple size distribution in different local environments (band gap) observed in this work could be used for the fabrication of light emission diodes (LEDs) or shift-conversion thin films in third generation efficient tandem solar cells for the maximum absorption of the solar spectrum in different wavelength regions.

Applications of Skyrme energy-density functional to fusion reactions spanning the fusion barriers

International Nuclear Information System (INIS)

Liu Min; Wang, Ning; Li Zhuxia; Wu Xizhen; Zhao Enguang

2006-01-01

The Skyrme energy density functional has been applied to the study of heavy-ion fusion reactions. The barriers for fusion reactions are calculated by the Skyrme energy density functional with proton and neutron density distributions determined by using restricted density variational (RDV) method within the same energy density functional together with semi-classical approach known as the extended semi-classical Thomas-Fermi method. Based on the fusion barrier obtained, we propose a parametrization of the empirical barrier distribution to take into account the multi-dimensional character of real barrier and then apply it to calculate the fusion excitation functions in terms of barrier penetration concept. A large number of measured fusion excitation functions spanning the fusion barriers can be reproduced well. The competition between suppression and enhancement effects on sub-barrier fusion caused by neutron-shell-closure and excess neutron effects is studied

Isobaric-Isothermal Molecular Dynamics Utilizing Density Functional Theory: An Assessment of the Structure and Density of Water at Near-Ambient Conditions

International Nuclear Information System (INIS)

Schmidt, J.; VandeVondele, J.; Kuo, I.W.; Sebastiani, D.; Siepmann, J.I.; Hutter, J.; Mundy, C.J.

2009-01-01

We present herein a comprehensive density functional theory study toward assessing the accuracy of two popular gradient-corrected exchange correlation functionals on the structure and density of liquid water at near ambient conditions in the isobaric-isothermal ensemble. Our results indicate that both PBE and BLYP functionals under predict the density and over structure the liquid. Adding the dispersion correction due to Grimme(1, 2) improves the predicted densities for both BLYP and PBE in a significant manner. Moreover, the addition of the dispersion correction for BLYP yields an oxygen-oxygen radial distribution function in excellent agreement with experiment. Thus, we conclude that one can obtain a very satisfactory model for water using BLYP and a correction for dispersion.

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)

A density functional theory study of magneto-electric Jones birefringence of noble gases, furan homologues, and mono-substituted benzenes

International Nuclear Information System (INIS)

Fahleson, Tobias; Norman, Patrick; Coriani, Sonia; Rizzo, Antonio; Rikken, Geert L. J. A.

2013-01-01

We report on the results of a systematic ab initio study of the Jones birefringence of noble gases, of furan homologues, and of monosubstituted benzenes, in the gas phase, with the aim of analyzing the behavior and the trends within a list of systems of varying size and complexity, and of identifying candidates for a combined experimental/theoretical study of the effect. We resort here to analytic linear and nonlinear response functions in the framework of time-dependent density functional theory. A correlation is made between the observable (the Jones constant) and the atomic radius for noble gases, or the permanent electric dipole and a structure/chemical reactivity descriptor as the para Hammett constant for substituted benzenes

Metallacarboranes and their interactions: theoretical insights and their applicability

Czech Academy of Sciences Publication Activity Database

Farras, P.; Juárez-Pérez, E. J.; Lepšík, Martin; Luque, R.; Núnez, R.; Teixidor, F.

2012-01-01

Roč. 41, č. 9 (2012), s. 3445-3463 ISSN 0306-0012 R&D Projects: GA AV ČR IAAX00320901 Institutional research plan: CEZ:AV0Z40550506 Keywords : density-functional theory * nonlinear-optical properties * NMR chemical-shifts * HIV protease * sandwich complexes Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 24.892, year: 2012

The chirally rotated Schroedinger functional. Theoretical expectations and perturbative tests

International Nuclear Information System (INIS)

Dalla Brida, Mattia

2016-03-01

The chirally rotated Schroedinger functional (χSF) with massless Wilson-type fermions provides an alternative lattice regularization of the Schroedinger functional (SF), with different lattice symmetries and a common continuum limit expected from universality. The explicit breaking of flavour and parity symmetries needs to be repaired by tuning the bare fermion mass and the coefficient of a dimension 3 boundary counterterm. Once this is achieved one expects the mechanism of automatic O(a) improvement to be operational in the χSF, in contrast to the standard formulation of the SF. This is expected to significantly improve the attainable precision for step-scaling functions of some composite operators. Furthermore, the χSF offers new strategies to determine finite renormalization constants which are traditionally obtained from chiral Ward identities. In this paper we consider a complete set of fermion bilinear operators, define corresponding correlation functions and explain the relation to their standard SF counterparts. We discuss renormalization and O(a) improvement and then use this set-up to formulate the theoretical expectations which follow from universality. Expanding the correlation functions to one-loop order of perturbation theory we then perform a number of non-trivial checks. In the process we obtain the action counterterm coefficients to one-loop order and reproduce some known perturbative results for renormalization constants of fermion bilinears. By confirming the theoretical expectations, this perturbative study lends further support to the soundness of the χSF framework and prepares the ground for non-perturbative applications.

Density functional application to strongly correlated electron systems

International Nuclear Information System (INIS)

Eschrig, H.; Koepernik, K.; Chaplygin, I.

2003-01-01

The local spin density approximation plus onsite Coulomb repulsion approach (LSDA+U) to density functional theory is carefully reanalyzed. Its possible link to single-particle Green's function theory is occasionally discussed. A simple and elegant derivation of the important sum rules for the on-site interaction matrix elements linking them to the values of U and J is presented. All necessary expressions for an implementation of LSDA+U into a non-orthogonal basis solver for the Kohn-Sham equations are given, and implementation into the full-potential local-orbital solver (Phys. Rev. B 59 (1999) 1743) is made. Results of application to several planar cuprate structures are reported in detail and conclusions on the interpretation of the physics of the electronic structure of the cuprates are drawn

Magneto-structural correlations in trinuclear Cu(II) complexes: a density functional study

CERN Document Server

Rodríguez-Forteá, A; Alvarez, S; Centre-De Recera-En-Quimica-Teorica; Alemany, P A; Centre-De Recera-En-Quimica-Teorica

2003-01-01

Density functional theoretical methods have been used to study magneto-structural correlations for linear trinuclear hydroxo-bridged copper(II) complexes. The nearest-neighbor exchange coupling constant shows very similar trends to those found earlier for dinuclear compounds for which the Cu-O-Cu angle and the out of plane displacement of the hydrogen atoms at the bridge are the two key structural factors that determine the nature of their magnetic behavior. Changes in these two parameters can induce variations of over 1000 cm sup - sup 1 in the value of the nearest-neighbor coupling constant. On the contrary, coupling between next-nearest neighbors is found to be practically independent of structural changes with a value for the coupling constant of about -60 cm sup - sup 1. The magnitude calculated for this coupling constant indicates that considering its value to be negligible, as usually done in experimental studies, can lead to considerable errors, especially for compounds in which the nearest-neighbor c...

Density-correlation functions in Calogero-Sutherland models

International Nuclear Information System (INIS)

Minahan, J.A.; Polychronakos, A.P.

1994-01-01

Using arguments from two-dimensional Yang-Mills theory and the collective coordinate formulation of the Calogero-Sutherland model, we conjecture the dynamical density-correlation function for coupling l and 1/l, where l is an integer. We present overwhelming evidence that the conjecture is indeed correct

Density correlation functions in Calogero-Sutherland models

CERN Document Server

Minahan, Joseph A.; Joseph A Minahan; Alexios P Polychronakos

1994-01-01

Using arguments from two dimensional Yang-Mills theory and the collective coordinate formulation of the Calogero-Sutherland model, we conjecture the dynamical density correlation function for coupling l and 1/l, where l is an integer. We present overwhelming evidence that the conjecture is indeed correct.

Multiconfiguration pair-density functional theory: barrier heights and main group and transition metal energetics.

Science.gov (United States)

Carlson, Rebecca K; Li Manni, Giovanni; Sonnenberger, Andrew L; Truhlar, Donald G; Gagliardi, Laura

2015-01-13

Kohn-Sham density functional theory, resting on the representation of the electronic density and kinetic energy by a single Slater determinant, has revolutionized chemistry, but for open-shell systems, the Kohn-Sham Slater determinant has the wrong symmetry properties as compared to an accurate wave function. We have recently proposed a theory, called multiconfiguration pair-density functional theory (MC-PDFT), in which the electronic kinetic energy and classical Coulomb energy are calculated from a multiconfiguration wave function with the correct symmetry properties, and the rest of the energy is calculated from a density functional, called the on-top density functional, that depends on the density and the on-top pair density calculated from this wave function. We also proposed a simple way to approximate the on-top density functional by translation of Kohn-Sham exchange-correlation functionals. The method is much less expensive than other post-SCF methods for calculating the dynamical correlation energy starting with a multiconfiguration self-consistent-field wave function as the reference wave function, and initial tests of the theory were quite encouraging. Here, we provide a broader test of the theory by applying it to bond energies of main-group molecules and transition metal complexes, barrier heights and reaction energies for diverse chemical reactions, proton affinities, and the water dimerization energy. Averaged over 56 data points, the mean unsigned error is 3.2 kcal/mol for MC-PDFT, as compared to 6.9 kcal/mol for Kohn-Sham theory with a comparable density functional. MC-PDFT is more accurate on average than complete active space second-order perturbation theory (CASPT2) for main-group small-molecule bond energies, alkyl bond dissociation energies, transition-metal-ligand bond energies, proton affinities, and the water dimerization energy.

True density and apparent density during the drying process for vegetables and fruits: a review.

Science.gov (United States)

Rodríguez-Ramírez, J; Méndez-Lagunas, L; López-Ortiz, A; Torres, S Sandoval

2012-12-01

This review presents the concepts involved in determining the density of foodstuffs, and summarizes the volumetric determination techniques used to calculate true density and apparent density in foodstuffs exposed to the drying process. The behavior of density with respect to moisture content (X) and drying temperature (T) is presented and explained with a basis in changes in structure, conformation, chemical composition, and second-order phase changes that occur in the processes of mass and heat transport, as reported to date in the literature. A review of the empirical and theoretical equations that represent density is presented, and their application in foodstuffs is discussed. This review also addresses cases with nonideal density behavior, including variations in ρ(s) and ρ(w) as a function of the inside temperature of the material, depending on drying conditions (X, T). A compilation of studies regarding the density of dehydrated foodstuffs is also presented. © 2012 Institute of Food Technologists®

Development of gradient-corrected exchange-correlation functionals in the density functional theory; Developpement de fonctionnelles corrigees du gradient en theorie de la fonctionnelle de la densite

Energy Technology Data Exchange (ETDEWEB)

Lembarki, A.

1994-12-01

In this work, we have developed some gradient-corrected exchange-correlation functionals. This study is in keeping with the density functional theory (DFT) formalism. In the first part of this memory, a description of Hartree-Fock (HF), post-HF and density functional theories is given. The second part is devoted the study the different approximations of DFT exchange-correlation functionals which have been proposed in the last years. In particular, we have underlined the approximations used for the construction of these functionals. The third part of this memory consists in the development of new gradient-corrected functionals. In this study, we have established a new relation between exchange energy, correlation energy and kinetic energy. We have deduced two new possible forms of exchange or correlation functionals, respectively. In the fourth part, we have studied the exchange potential, for which the actual formulation does not satisfy some theoretical conditions, such as the asymptotic behavior -1/r. Our contribution lies in the development of an exchange potential with a correct asymptotic -1/r behavior for large values of r. In this chapter, we have proposed a model which permits the obtention of the exchange energy from the exchange potential, using the virial theorem. The fifth part of this memory is devoted the application of these different functionals to simple systems (H{sub 2}O, CO, N{sub 2}O, H{sub 3}{sup +} and H{sub 5}{sup +}) in order to characterize the performance of DFT calculations in regards to those obtained with post-HF methods. (author). 215 refs., 8 figs., 28 tabs.

Level Densities and Radiative Strength Functions in 170,171Yb

International Nuclear Information System (INIS)

Agvaanluvsan, U.; Schiller, A.; Becker, J.A.; Berstein, L.A.; Guttormsen, M.; Mitchell, G.E.; Rekstad, J.; Siem, S.; Voinov, A.

2003-01-01

Level densities and radiative strength functions in 171 Yb and 170 Yb nuclei have been measured with the 171 Yb( 3 He, 3 He(prime) γ) 171 Yb and 171 Yb( 3 He, αγ) 170 Yb reactions. A simultaneous determination of the nuclear level density and the radiative strength function was made. The present data adds to and is consistent with previous results for several other rare earth nuclei. The method will be briefly reviewed and the result from the analysis will be presented. The radiative strength function for 171 Yb is compared to previously published work.

Treatment of Layered Structures Using a Semilocal meta-GGA Density Functional

DEFF Research Database (Denmark)

Madsen, Georg; Ferrighi, Lara; Hammer, Bjørk

2010-01-01

Density functional theory calculations on solids consisting of covalently bonded layers held together by dispersive interactions are presented. Utilizing the kinetic energy density in addition to the density and its gradients gives the meta-generalized gradient approximation (MGGA) M06-L enough...

Navigating Glycerol Conversion Roadmap and Heterogeneous Catalyst Selection Aided by Density Functional Theory: A Review

Directory of Open Access Journals (Sweden)

Bin Liu

2018-01-01

Full Text Available Glycerol has been utilized in an extremely diversified manner throughout human civilization—ranging from food, to various consumer products, to pharmaceuticals, and even explosives. Large surplus in glycerol supply thanks to biodiesel production and biomass processing has created a demand to further boost its utility. One growing area is to expand the use of glycerol as an alternative feedstock to supplement fuels and chemicals production. Various catalytic processes have been developed. This review summarizes catalytic materials for glycerol reforming, hydrodeoxygenation, and oxidation. In particular, rationale for catalyst selection and new catalyst design will be discussed aided by the knowledge of reaction mechanisms. The role of theoretical density functional theory (DFT in elucidating complex glycerol conversion chemistries is particularly emphasized.

Theoretical Characteristics of Metalloporphyrins (OEP) M (CH 3 ) (M=Al, Ga, In and Tl)

OpenAIRE

Lepetit , M.B.; Kabbaj , O.K.; Zrineh , A.

2017-01-01

International audience; A theoretical study of metalloporphyrins molecules (OEP) M (CH 3) (M=Al, Ga, In and Tl) are brought to a few experimental data and to give background for future development of these complexes. The Quantum Chemistry Program (ORCA) program package based on Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TDDFT) for transitions at the B3LYP level with ANO 2ζ+P base was used for calculations and determination of structural properties, electroni...

Trajectory-based nonadiabatic dynamics with time-dependent density functional theory.

Science.gov (United States)

Curchod, Basile F E; Rothlisberger, Ursula; Tavernelli, Ivano

2013-05-10

Understanding the fate of an electronically excited molecule constitutes an important task for theoretical chemistry, and practical implications range from the interpretation of atto- and femtosecond spectroscopy to the development of light-driven molecular machines, the control of photochemical reactions, and the possibility of capturing sunlight energy. However, many challenging conceptual and technical problems are involved in the description of these phenomena such as 1) the failure of the well-known Born-Oppenheimer approximation; 2) the need for accurate electronic properties such as potential energy surfaces, excited nuclear forces, or nonadiabatic coupling terms; and 3) the necessity of describing the dynamics of the photoexcited nuclear wavepacket. This review provides an overview of the current methods to address points 1) and 3) and shows how time-dependent density functional theory (TDDFT) and its linear-response extension can be used for point 2). First, the derivation of Ehrenfest dynamics and nonadiabatic Bohmian dynamics is discussed and linked to Tully's trajectory surface hopping. Second, the coupling of these trajectory-based nonadiabatic schemes with TDDFT is described in detail with special emphasis on the derivation of the required electronic structure properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Density-functional study on the equilibria in the ThDP activation.

Science.gov (United States)

Delgado, Eduardo J; Alderete, Joel B; Jaña, Gonzalo A

2011-11-01

The equilibria among the various ionization and tautomeric states involved in the activation of ThDP is addressed using high level density functional theory calculations, X3LYP/6-311++G(d,p)//X3LYP(PB)/6-31++G(d,p). This study provides the first theoretically derived thermodynamic data for the internal equilibria in the activation of ThDP. The role of the medium polarity on the geometry and thermodynamics of the diverse equilibria of ThDP is addressed. The media chosen are cyclohexane and water, as paradigms of apolar and polar media. The results suggest that all ionization and tautomeric states are accessible during the catalytic cycle, even in the absence of substrate, being APH(+) the form required to interconvert the AP and IP tautomers; and the generation of the ylide proceeds via the formation of the IP form. Additionally, the calculated ΔG° values allow to calculate all the equilibrium constants, including the pK(C2) for the thiazolium C2 atom whose ionization is believed to initiate the catalytic cycle.

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.

Probability density function method for variable-density pressure-gradient-driven turbulence and mixing

International Nuclear Information System (INIS)

Bakosi, Jozsef; Ristorcelli, Raymond J.

2010-01-01

Probability density function (PDF) methods are extended to variable-density pressure-gradient-driven turbulence. We apply the new method to compute the joint PDF of density and velocity in a non-premixed binary mixture of different-density molecularly mixing fluids under gravity. The full time-evolution of the joint PDF is captured in the highly non-equilibrium flow: starting from a quiescent state, transitioning to fully developed turbulence and finally dissipated by molecular diffusion. High-Atwood-number effects (as distinguished from the Boussinesq case) are accounted for: both hydrodynamic turbulence and material mixing are treated at arbitrary density ratios, with the specific volume, mass flux and all their correlations in closed form. An extension of the generalized Langevin model, originally developed for the Lagrangian fluid particle velocity in constant-density shear-driven turbulence, is constructed for variable-density pressure-gradient-driven flows. The persistent small-scale anisotropy, a fundamentally 'non-Kolmogorovian' feature of flows under external acceleration forces, is captured by a tensorial diffusion term based on the external body force. The material mixing model for the fluid density, an active scalar, is developed based on the beta distribution. The beta-PDF is shown to be capable of capturing the mixing asymmetry and that it can accurately represent the density through transition, in fully developed turbulence and in the decay process. The joint model for hydrodynamics and active material mixing yields a time-accurate evolution of the turbulent kinetic energy and Reynolds stress anisotropy without resorting to gradient diffusion hypotheses, and represents the mixing state by the density PDF itself, eliminating the need for dubious mixing measures. Direct numerical simulations of the homogeneous Rayleigh-Taylor instability are used for model validation.

Experimental-theoretical approach to carbon monoxide density calculation at the incipient stage of the fire indoors

Science.gov (United States)

Puzach, S. V.; Suleykin, E. V.; Akperov, R. G.; Nguyen, T. D.

2017-11-01

A new experimental-theoretical approach to the toxic gases concentrations assessment in case of fire indoors is offered. The analytical formulas for calculation of CO average volume density are received. These formulas do not contain the geometrical sizes of the room and surfaces dimensions of combustible materials and, therefore, are valid under conditions of as a small-scale fire as a large-scale fire. A small-scale experimental installation for modeling fire thermal and gas dynamics in the closed or open thermodynamic system has been designed. The results of the experiments on determining dependencies of CO average volume density from average volume temperature and oxygen average volume density as well as dependencies of specific coefficients of CO emission and specific mass rates of the combustible material gasification from the time of tests during the burning of wood, transformer oil and PVC cables shield are presented. The results of numerical experiments on CO density calculation in small and large scale rooms using the proposed analytical solutions, integral, zone and field models for calculation of fire thermal and gas dynamics are presented. The comparison with the experimental data obtained by the authors and given in the literature has been performed. It is shown that CO density calculation in the full-scale room at the incipient stage of the fire can be carried out taking into account only the experimental dependences of CO from temperature or O2 density, that have been obtained from small-scale experiments. Therefore the solution of the equation of carbon monoxide mass conservation law is not necessary.

Theoretical and experimental study of fenofibrate and simvastatin

Science.gov (United States)

Nicolás Vázquez, Inés; Rodríguez-Núñez, Jesús Rubén; Peña-Caballero, Vicente; Ruvalcaba, Rene Miranda; Aceves-Hernandez, Juan Manuel

2017-12-01

Fenofibrate, an oral fibrate lipid lowering agent, and simvastatin, which reduces plasma levels of low-density lipoprotein cholesterol, are active pharmaceutical ingredients (APIs), currently in the market. We characterized these APIs by thermal analysis and conducted X-ray powder diffraction techniques. Studies should be carried out in the formulation stage before the final composition of a polypill may be established. Thus, it was found in thermochemical studies that both compounds present no chemical interactions in an equimolar mixture of solid samples at room temperature. Theoretical studies were employed to determine possible interactions between fenofibrate and simvastatin. A very weak intramolecular hydrogen bond is formed between the hydroxyl group (O5H5) of the simvastatin with chlorine and carbonyl group (C11O4, C1O2) of the fenofibrate molecule. These weak energy hydrogen bonds have no effect on the chemical stability of the compounds studied. The results were obtained using Density Functional Theory methods; particularly the BPE1BPE and B3LYP functional and 6-31++G** basis set. The values of energy show good approximation when are compared with similar calculations previously reported. Infrared spectra of monomers and dimers were obtained via theoretical calculations.

Bovine serum albumin adsorption onto functionalized polystyrene lattices: A theoretical modeling approach and error analysis

Science.gov (United States)

Beragoui, Manel; Aguir, Chadlia; Khalfaoui, Mohamed; Enciso, Eduardo; Torralvo, Maria José; Duclaux, Laurent; Reinert, Laurence; Vayer, Marylène; Ben Lamine, Abdelmottaleb

2015-03-01

The present work involves the study of bovine serum albumin adsorption onto five functionalized polystyrene lattices. The adsorption measurements have been carried out using a quartz crystal microbalance. Poly(styrene-co-itaconic acid) was found to be an effective adsorbent for bovine serum albumin molecule adsorption. The experimental isotherm data were analyzed using theoretical models based on a statistical physics approach, namely monolayer, double layer with two successive energy levels, finite multilayer, and modified Brunauer-Emmet-Teller. The equilibrium data were then analyzed using five different non-linear error analysis methods and it was found that the finite multilayer model best describes the protein adsorption data. Surface characteristics, i.e., surface charge density and number density of surface carboxyl groups, were used to investigate their effect on the adsorption capacity. The combination of the results obtained from the number of adsorbed layers, the number of adsorbed molecules per site, and the thickness of the adsorbed bovine serum albumin layer allows us to predict that the adsorption of this protein molecule can also be distinguished by monolayer or multilayer adsorption with end-on, side-on, and overlap conformations. The magnitudes of the calculated adsorption energy indicate that bovine serum albumin molecules are physisorbed onto the adsorbent lattices.

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.

Modeling goals and functions of control and safety systems - theoretical foundations and extensions of MFM

International Nuclear Information System (INIS)

Lind, M.

2005-10-01

Multilevel Flow Modeling (MFM) has proven to be an effective modeling tool for reasoning about plant failure and control strategies and is currently exploited for operator support in diagnosis and on-line alarm analysis. Previous MFM research was focussed on representing goals and functions of process plants which generate, transform and distribute mass and energy. However, only a limited consideration has been given to the problems of modeling the control systems. Control functions are indispensable for operating any industrial plant. But modeling of control system functions has proven to be a more challenging problem than modeling functions of energy and mass processes. The problems were discussed by Lind and tentative solutions has been proposed but have not been investigated in depth until recently, partly due to the lack of an appropriate theoretical foundation. The purposes of the present report are to show that such a theoretical foundation for modeling goals and functions of control systems can be built from concepts and theories of action developed by Von Wright and to show how the theoretical foundation can be used to extend MFM with concepts for modeling control systems. The theoretical foundations has been presented in detail elsewhere by the present author without the particular focus on modeling control actions and MFM adopted here. (au)

Modeling goals and functions of control and safety systems -theoretical foundations and extensions of MFM

Energy Technology Data Exchange (ETDEWEB)

Lind, M. [Oersted - DTU, Kgs. Lyngby (Denmark)

2005-10-01

Multilevel Flow Modeling (MFM) has proven to be an effective modeling tool for reasoning about plant failure and control strategies and is currently exploited for operator support in diagnosis and on-line alarm analysis. Previous MFM research was focussed on representing goals and functions of process plants which generate, transform and distribute mass and energy. However, only a limited consideration has been given to the problems of modeling the control systems. Control functions are indispensable for operating any industrial plant. But modeling of control system functions has proven to be a more challenging problem than modeling functions of energy and mass processes. The problems were discussed by Lind and tentative solutions has been proposed but have not been investigated in depth until recently, partly due to the lack of an appropriate theoretical foundation. The purposes of the present report are to show that such a theoretical foundation for modeling goals and functions of control systems can be built from concepts and theories of action developed by Von Wright and to show how the theoretical foundation can be used to extend MFM with concepts for modeling control systems. The theoretical foundations has been presented in detail elsewhere by the present author without the particular focus on modeling control actions and MFM adopted here. (au)

Theoretical Neuroanatomy:Analyzing the Structure, Dynamics,and Function of Neuronal Networks

Science.gov (United States)

Seth, Anil K.; Edelman, Gerald M.

The mammalian brain is an extraordinary object: its networks give rise to our conscious experiences as well as to the generation of adaptive behavior for the organism within its environment. Progress in understanding the structure, dynamics and function of the brain faces many challenges. Biological neural networks change over time, their detailed structure is difficult to elucidate, and they are highly heterogeneous both in their neuronal units and synaptic connections. In facing these challenges, graph-theoretic and information-theoretic approaches have yielded a number of useful insights and promise many more.

Study of nuclear level density parameter and its temperature dependence

International Nuclear Information System (INIS)

Nasrabadi, M. N.; Behkami, A. N.

2000-01-01

The nuclear level density ρ is the basic ingredient required for theoretical studies of nuclear reaction and structure. It describes the statistical nuclear properties and is expressed as a function of various constants of motion such as number of particles, excitation energy and angular momentum. In this work the energy and spin dependence of nuclear level density will be presented and discussed. In addition the level density parameter α will be extracted from this level density information, and its temperature and mass dependence will be obtained

Efficient molecular density functional theory using generalized spherical harmonics expansions.

Science.gov (United States)

Ding, Lu; Levesque, Maximilien; Borgis, Daniel; Belloni, Luc

2017-09-07

We show that generalized spherical harmonics are well suited for representing the space and orientation molecular density in the resolution of the molecular density functional theory. We consider the common system made of a rigid solute of arbitrary complexity immersed in a molecular solvent, both represented by molecules with interacting atomic sites and classical force fields. The molecular solvent density ρ(r,Ω) around the solute is a function of the position r≡(x,y,z) and of the three Euler angles Ω≡(θ,ϕ,ψ) describing the solvent orientation. The standard density functional, equivalent to the hypernetted-chain closure for the solute-solvent correlations in the liquid theory, is minimized with respect to ρ(r,Ω). The up-to-now very expensive angular convolution products are advantageously replaced by simple products between projections onto generalized spherical harmonics. The dramatic gain in speed of resolution enables to explore in a systematic way molecular solutes of up to nanometric sizes in arbitrary solvents and to calculate their solvation free energy and associated microscopic solvent structure in at most a few minutes. We finally illustrate the formalism by tackling the solvation of molecules of various complexities in water.

Probability-density-function characterization of multipartite entanglement

International Nuclear Information System (INIS)

Facchi, P.; Florio, G.; Pascazio, S.

2006-01-01

We propose a method to characterize and quantify multipartite entanglement for pure states. The method hinges upon the study of the probability density function of bipartite entanglement and is tested on an ensemble of qubits in a variety of situations. This characterization is also compared to several measures of multipartite entanglement

Higher-order terms in the nuclear-energy-density functional

International Nuclear Information System (INIS)

Carlsson, B. G.; Borucki, M.; Dobaczewski, J.

2009-01-01

One of the current projects at the Department of Physics in the University of Jyvaeskylae is to explore more general forms of the Skyrme energy-density functional (EDF). The aim is to find new phenomenological terms which are sensitive to experimental data. In this context we have extended the Skyrme functional by including terms which contain higher orders of derivatives allowing for a better description of finite range effects. This was done by employing an expansion in derivatives in a spherical-tensor formalism [1] motivated by ideas of the density-matrix expansion. The resulting functionals have different number of free parameters depending on the order in derivatives and assumed symmetries, see Fig. 1. The usual Skyrme EDF is obtained as a second order expansion while we keep terms up to sixth order.(author)

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.)

Pressure and surface tension of soild-liquid interface using Tarazona density functional theory

Directory of Open Access Journals (Sweden)

M. M.

2000-12-01

Full Text Available   The weighted density functional theory proposed by Tarazona is applied to study the solid-liquid interface. In the last two decades the weighted density functional became a useful tool to consider the properties of inhomogeneous liquids. In this theory, the role of the size of molecules or the particles of which the matter is composed, was found to be important. In this resarch we study a hard sphere fluid beside a hard wall. For this study the liquid is an inhomogeneous system. We use the definition of the direct correlation function as a second derivative of free energy with respect to the density. We use this definition and the definition of the weighting function, then we minimize the grand potential with respect to the density to get the Euler Lagrange equation and we obtain an integral equation to find the inhomogeneous density profile. The obtained density profile as a function of the distance from the wall, for different bulk density is plotted in three dimensions. We also calculate the pressure and compare it with the Carnahan-starling results, and finally we obtained the surface tension at liquid-solid interface and compared it with the results of Monte Carlo simulation.

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.

Restoring the consistency with the contact density theorem of a classical density functional theory of ions at a planar electrical double layer.

Science.gov (United States)

Gillespie, Dirk

2014-11-01

Classical density functional theory (DFT) of fluids is a fast and efficient theory to compute the structure of the electrical double layer in the primitive model of ions where ions are modeled as charged, hard spheres in a background dielectric. While the hard-core repulsive component of this ion-ion interaction can be accurately computed using well-established DFTs, the electrostatic component is less accurate. Moreover, many electrostatic functionals fail to satisfy a basic theorem, the contact density theorem, that relates the bulk pressure, surface charge, and ion densities at their distances of closest approach for ions in equilibrium at a smooth, hard, planar wall. One popular electrostatic functional that fails to satisfy the contact density theorem is a perturbation approach developed by Kierlik and Rosinberg [Phys. Rev. A 44, 5025 (1991)PLRAAN1050-294710.1103/PhysRevA.44.5025] and Rosenfeld [J. Chem. Phys. 98, 8126 (1993)JCPSA60021-960610.1063/1.464569], where the full free-energy functional is Taylor-expanded around a bulk (homogeneous) reference fluid. Here, it is shown that this functional fails to satisfy the contact density theorem because it also fails to satisfy the known low-density limit. When the functional is corrected to satisfy this limit, a corrected bulk pressure is derived and it is shown that with this pressure both the contact density theorem and the Gibbs adsorption theorem are satisfied.

Correlation functional in screened-exchange density functional theory procedures.

Science.gov (United States)

Chan, Bun; Kawashima, Yukio; Hirao, Kimihiko

2017-10-15

In the present study, we have explored several prospects for the further development of screened-exchange density functional theory (SX-DFT) procedures. Using the performance of HSE06 as our measure, we find that the use of alternative correlation functionals (as oppose to PBEc in HSE06) also yields adequate results for a diverse set of thermochemical properties. We have further examined the performance of new SX-DFT procedures (termed HSEB-type methods) that comprise the HSEx exchange and a (near-optimal) reparametrized B97c (c OS,0  = c SS,0  = 1, c OS,1  = -1.5, c OS,2  = -0.644, c SS,1  = -0.5, and c SS,2  = 1.10) correlation functionals. The different variants of HSEB all perform comparably to or slightly better than the original HSE-type procedures. These results, together with our fundamental analysis of correlation functionals, point toward various directions for advancing SX-DFT methods. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Ultrasonic density detector for vessel and reactor core two-phase flow measurements

International Nuclear Information System (INIS)

Arave, A.E.

1979-01-01

A local ultrasonic density (LUD) detector has been developed by EG and G Idaho, Inc., at the Idaho National Engineering Laboratory for the Loss-of-Fluid Test (LOFT) reactor vessel and core two-phase flow density measurements. The principle of operating the sensor is the change in propagation time of a torsional ultrasonic wave in a metal transmission line as a function of the density of the surrounding media. A theoretical physics model is presented which represents the total propagation time as a function of the sensor modulus of elasticity and polar moment of inertia

Theoretical stellar luminosity functions and globular cluster ages and compositions

International Nuclear Information System (INIS)

Ratcliff, S.J.

1985-01-01

The ages and chemical compositions of the stars in globular clusters are of great interest, particularly because age estimates from the well-known exercise of fitting observed color-magnitude diagrams to theoretical predictions tend to yield ages in excess of the Hubble time (an estimate to the age of the Universe) in standard cosmological models, for currently proposed high values of Hubble's constant (VandenBerg 1983). Relatively little use has been made of stellar luminosity functions of the globular clusters, for which reliable observations are now becoming available, to constrain the ages or compositions. The comparison of observed luminosity functions to theoretical ones allows one to take advantage of information not usually used, and has the advantage of being relatively insensitive to our lack of knowledge of the detailed structure of stellar envelopes and atmospheres. A computer program was developed to apply standard stellar evolutionary theory, using the most recently available input physics (opacities, nuclear reaction rates), to the calculation of the evolution of low-mass Population II stars. An algorithm for computing luminosity functions from the evolutionary tracks was applied to sets of tracks covering a broad range of chemical compositions and ages, such as may be expected for globular clusters

Density-functional errors in ionization potential with increasing system size

Energy Technology Data Exchange (ETDEWEB)

Whittleton, Sarah R.; Sosa Vazquez, Xochitl A.; Isborn, Christine M., E-mail: cisborn@ucmerced.edu [Chemistry and Chemical Biology, School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343 (United States); Johnson, Erin R., E-mail: erin.johnson@dal.ca [Chemistry and Chemical Biology, School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343 (United States); Department of Chemistry, Dalhousie University, 6274 Coburg Road, Halifax, Nova Scotia B3H 4R2 (Canada)

2015-05-14

This work investigates the effects of molecular size on the accuracy of density-functional ionization potentials for a set of 28 hydrocarbons, including series of alkanes, alkenes, and oligoacenes. As the system size increases, delocalization error introduces a systematic underestimation of the ionization potential, which is rationalized by considering the fractional-charge behavior of the electronic energies. The computation of the ionization potential with many density-functional approximations is not size-extensive due to excessive delocalization of the incipient positive charge. While inclusion of exact exchange reduces the observed errors, system-specific tuning of long-range corrected functionals does not generally improve accuracy. These results emphasize that good performance of a functional for small molecules is not necessarily transferable to larger systems.

A Density Functional for Liquid 3He Based on the Aziz Potential

Science.gov (United States)

Barranco, M.; Hernández, E. S.; Mayol, R.; Navarro, J.; Pi, M.; Szybisz, L.

2006-09-01

We propose a new class of density functionals for liquid 3He based on the Aziz helium-helium interaction screened at short distances by the microscopically calculated two-body distribution function g(r). Our aim is to reduce to a minumum the unavoidable phenomenological ingredients inherent to any density functional approach. Results for the homogeneous liquid and droplets are presented and discussed.

Fast Computation of Solvation Free Energies with Molecular Density Functional Theory: Thermodynamic-Ensemble Partial Molar Volume Corrections.

Science.gov (United States)

Sergiievskyi, Volodymyr P; Jeanmairet, Guillaume; Levesque, Maximilien; Borgis, Daniel

2014-06-05

Molecular density functional theory (MDFT) offers an efficient implicit-solvent method to estimate molecule solvation free-energies, whereas conserving a fully molecular representation of the solvent. Even within a second-order approximation for the free-energy functional, the so-called homogeneous reference fluid approximation, we show that the hydration free-energies computed for a data set of 500 organic compounds are of similar quality as those obtained from molecular dynamics free-energy perturbation simulations, with a computer cost reduced by 2-3 orders of magnitude. This requires to introduce the proper partial volume correction to transform the results from the grand canonical to the isobaric-isotherm ensemble that is pertinent to experiments. We show that this correction can be extended to 3D-RISM calculations, giving a sound theoretical justification to empirical partial molar volume corrections that have been proposed recently.

On Farmer's line, probability density functions, and overall risk

International Nuclear Information System (INIS)

Munera, H.A.; Yadigaroglu, G.

1986-01-01

Limit lines used to define quantitative probabilistic safety goals can be categorized according to whether they are based on discrete pairs of event sequences and associated probabilities, on probability density functions (pdf's), or on complementary cumulative density functions (CCDFs). In particular, the concept of the well-known Farmer's line and its subsequent reinterpretations is clarified. It is shown that Farmer's lines are pdf's and, therefore, the overall risk (defined as the expected value of the pdf) that they represent can be easily calculated. It is also shown that the area under Farmer's line is proportional to probability, while the areas under CCDFs are generally proportional to expected value

Density functional and many-body theories of Hydrogen plasmas

International Nuclear Information System (INIS)

Perrot, F.; Dharma-Wardana, M.W.C.

1983-11-01

This work is an attempt to go beyond the standard description of hot condensed matter using the well-known ''average atom model''. The first part describes a static model using ''Density functional theory'' to calculate self-consistent coupled electron and ion density profiles of the plasma not restricted to a single average atomic sphere. In a second part, the results are used as ingredients for a many-body approach to electronic properties: the one-particle Green-function self-energy is calculated, from which shifted levels, populations and level-widths are deduced. Results for the Hydrogen plasma are reported, with emphasis on the 1s bound state

Ground-state properties of third-row elements with nonlocal density functionals

International Nuclear Information System (INIS)

Bagno, P.; Jepsen, O.; Gunnarsson, O.

1989-01-01

The cohesive energy, the lattice parameter, and the bulk modulus of third-row elements are calculated using the Langreth-Mehl-Hu (LMH), the Perdew-Wang (PW), and the gradient expansion functionals. The PW functional is found to give somewhat better results than the LMH functional and both are found to typically remove half the errors in the local-spin-density (LSD) approximation, while the gradient expansion gives worse results than the local-density approximation. For Fe both the LMH and PW functionals correctly predict a ferromagnetic bcc ground state, while the LSD approximation and the gradient expansion predict a nonmagnetic fcc ground state

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

Density-dependent Hartree-Fock response functions in quasi-elastic electron scattering on 12C and related sum rules

International Nuclear Information System (INIS)

Kohno, M.

1983-01-01

We report fully consistent calculations of the longitudinal and transverse response functions of the inclusive quasi-elastic electron scattering on 12 C in the Hartree-Fock approximation. The distorted wave for the outgoing nucleon is constructed from the same non-local Hartree-Fock field as in the ground-state description. Thus the orthogonality and Pauli principle requirements are naturally satisfied. The theoretical prediction, based on the standard density-dependent effective interaction (GO force), shows a good correspondence to the experimental data. Since the calculated response functions automatically satisfy the relevant sum rule, this work illuminates the well-known puzzle concerning the longitudinal part, which remains to be solved. We study the energy-weighted sum rules and discuss effects beyond the mean-field approximation. Meson-exchange-current contributions to the transverse response function are also estimated and found to be small due to cancellations among them. (orig.)

Spectroscopic and density functional theory studies of 5,7,3‧,5‧-tetrahydroxyflavanone from the leaves of Olea ferruginea

Science.gov (United States)

Hashmi, Muhammad Ali; Khan, Afsar; Ayub, Khurshid; Farooq, Umar

2014-07-01

5,7,3‧,5‧-Tetrahydroxyflavanone (1) was isolated from the leaves of Olea ferruginea and a theoretical model was developed for obtaining the electronic and spectroscopic properties of 1. The geometric and electronic properties were calculated at B3LYP/6-311 G (d, p) level of Density Functional Theory (DFT). The theoretical data was in good agreement with the experimental one. The optimized geometric parameters of compound 1 were calculated for the first time. The theoretical vibrational frequencies of 1 were found to correlate with the experimental IR spectrum after a scaling factor of 0.9811. The UV and NMR spectral data computed theoretically were in good agreement with the experimental data. Electronic properties of the compound i.e., ionization potential (IP), electron affinity (EA), coefficients of HOMO and LUMO were estimated computationally for the first time which can be used to explain its antioxidant as well as other related activities and more active sites on it. The intermolecular interactions and their effects on IR frequencies, electronic and geometric parameters were simulated using water molecule as a model for hydrogen bonding with flavonoid hydroxyl groups.

Solvent density inhomogeneities and solvation free energies in supercritical diatomic fluids: a density functional approach.

Science.gov (United States)

Husowitz, B; Talanquer, V

2007-02-07

Density functional theory is used to explore the solvation properties of a spherical solute immersed in a supercritical diatomic fluid. The solute is modeled as a hard core Yukawa particle surrounded by a diatomic Lennard-Jones fluid represented by two fused tangent spheres using an interaction site approximation. The authors' approach is particularly suitable for thoroughly exploring the effect of different interaction parameters, such as solute-solvent interaction strength and range, solvent-solvent long-range interactions, and particle size, on the local solvent structure and the solvation free energy under supercritical conditions. Their results indicate that the behavior of the local coordination number in homonuclear diatomic fluids follows trends similar to those reported in previous studies for monatomic fluids. The local density augmentation is particularly sensitive to changes in solute size and is affected to a lesser degree by variations in the solute-solvent interaction strength and range. The associated solvation free energies exhibit a nonmonotonous behavior as a function of density for systems with weak solute-solvent interactions. The authors' results suggest that solute-solvent interaction anisotropies have a major influence on the nature and extent of local solvent density inhomogeneities and on the value of the solvation free energies in supercritical solutions of heteronuclear molecules.

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)

Extending density functional embedding theory for covalently bonded systems.

Science.gov (United States)

Yu, Kuang; Carter, Emily A

2017-12-19

Quantum embedding theory aims to provide an efficient solution to obtain accurate electronic energies for systems too large for full-scale, high-level quantum calculations. It adopts a hierarchical approach that divides the total system into a small embedded region and a larger environment, using different levels of theory to describe each part. Previously, we developed a density-based quantum embedding theory called density functional embedding theory (DFET), which achieved considerable success in metals and semiconductors. In this work, we extend DFET into a density-matrix-based nonlocal form, enabling DFET to study the stronger quantum couplings between covalently bonded subsystems. We name this theory density-matrix functional embedding theory (DMFET), and we demonstrate its performance in several test examples that resemble various real applications in both chemistry and biochemistry. DMFET gives excellent results in all cases tested thus far, including predicting isomerization energies, proton transfer energies, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps for local chromophores. Here, we show that DMFET systematically improves the quality of the results compared with the widely used state-of-the-art methods, such as the simple capped cluster model or the widely used ONIOM method.

Are trinuclear superhalogens promising candidates for building blocks of novel magnetic materials? A theoretical prospect from combined broken-symmetry density functional theory and ab initio study.

Science.gov (United States)

Yu, Yang; Li, Chen; Yin, Bing; Li, Jian-Li; Huang, Yuan-He; Wen, Zhen-Yi; Jiang, Zhen-Yi

2013-08-07

The structures, relative stabilities, vertical electron detachment energies, and magnetic properties of a series of trinuclear clusters are explored via combined broken-symmetry density functional theory and ab initio study. Several exchange-correlation functionals are utilized to investigate the effects of different halogen elements and central atoms on the properties of the clusters. These clusters are shown to possess stronger superhalogen properties than previously reported dinuclear superhalogens. The calculated exchange coupling constants indicate the antiferromagnetic coupling between the transition metal ions. Spin density analysis demonstrates the importance of spin delocalization in determining the strengths of various couplings. Spin frustration is shown to occur in some of the trinuclear superhalogens. The coexistence of strong superhalogen properties and spin frustration implies the possibility of trinuclear superhalogens working as the building block of new materials of novel magnetic properties.

Vibrational and UV spectroscopic studies of 2-coumaranone by experimental and density functional theory calculations

Science.gov (United States)

Priya, Y. Sushma; Rao, K. Ramachandra; Chalapathi, P. V.; Satyavani, M.; Veeraiah, A.

2017-09-01

The vibrational and electronic properties of 2-coumaranone have been reported in the ground state using experimental techniques (FT-IR, FT-Raman, UV spectra and fluorescence microscopic imaging) and density functional theory (DFT) employing B3LYP correlation with the 6-31G(d, p) basis set. The theoretically reported optimized parameters, vibrational frequencies etc., were compared with the experimental values, which yielded good concurrence between the experimental and calculated values. The assignments of the vibrational spectra were done with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field(SQMFF) methodology. The whole assignments of fundamental modes were based on the potential energy distribution (PED) matrix. The electric dipole moment and the first order hyperpolarizability of the 2-coumaranone have been computed using quantum mechanical calculations. NBO and HOMO, LUMO analyses have been carried out. UV spectrum of 2-coumaranone was recorded in the region 100-300 nm and compared with the theoretical UV spectrum using TD-DFT and SAC-CI methods by which a good agreement is observed. Fluorescence microscopic imaging study reflects that the compound fluoresces in the green-yellow region.

A density functional theory study of the TMG adsorption on the GaN surface

Energy Technology Data Exchange (ETDEWEB)

Ptasinska, Maria; Soltys, Jakub; Piechota, Jacek [Interdisciplinary Centre for Materials Modelling, University of Warsaw, ul. Pawinskiego 5a, 02-106 Warszawa (Poland); Krukowski, Stanislaw [Interdisciplinary Centre for Materials Modelling, University of Warsaw, ul. Pawinskiego 5a, 02-106 Warszawa (Poland); Institute of High Pressure Physics, Polish Academy of Sciences, ul. Sokolowska 29/37, 01-142 Warsaw (Poland)

2011-07-01

TMG (trimetylogallium) and NH{sub 3} (ammonia) are widely used reactants in the metal organic chemical vapor deposition (MOCVD) technique used in the growth of the GaN thin films. We have recently examined theoretically, with the help of the density functional theory (DFT), TMG adsorption on the GaN(0001) surface in order to study formation of bonds between Ga and N. Dangling bonds on the GaN(0001) surface were saturated with the hydrogen atoms. The slab polarization, which is due to the dangling bonds present on the GaN(0001) surface, and energy of the system in the vicinity of TMG was computed for different distances between the surface atoms and TMG. We also studied TMG diffusion on the GaN surface. As a result, the energy path for diffusion from Top N to Hollow was obtained.

2nd derivatives of the electronic energy in density functional theory

Energy Technology Data Exchange (ETDEWEB)

Dam, H. van

2001-08-01

This document details the equations needed to implement the calculation of vibrational frequencies within the density functional formalism of electronic structure theory. This functionality has been incorporated into the CCP1 DFT module and the required changes to the application programmers interface are outlined. Throughout it is assumed that an implementation of Hartree-Fock vibrational frequencies is available that can be modified to incorporate the density functional formalism. Employing GAMESS-UK as an example the required changes to the Hartree-Fock code are outlined. (author)

The functional-cognitive meta-theoretical framework: Reflections, possible clarifications and how to move forward.

Science.gov (United States)

Barnes-Holmes, Dermot; Hussey, Ian

2016-02-01

The functional-cognitive meta-theoretical framework has been offered as a conceptual basis for facilitating greater communication and cooperation between the functional/behavioural and cognitive traditions within psychology, thus leading to benefits for both scientific communities. The current article is written from the perspective of two functional researchers, who are also proponents of the functional-cognitive framework, and attended the "Building Bridges between the Functional and Cognitive Traditions" meeting at Ghent University in the summer of 2014. The article commences with a brief summary of the functional approach to theory, followed by our reflections upon the functional-cognitive framework in light of that meeting. In doing so, we offer three ways in which the framework could be clarified: (a) effective communication between the two traditions is likely to be found at the level of behavioural observations rather than effects or theory, (b) not all behavioural observations will be deemed to be of mutual interest to both traditions, and (c) observations of mutual interest will be those that serve to elaborate and extend existing theorising in the functional and/or cognitive traditions. The article concludes with a summary of what we perceive to be the strengths and weaknesses of the framework, and a suggestion that there is a need to determine if the framework is meta-theoretical or is in fact a third theoretical approach to doing psychological science. © 2015 International Union of Psychological Science.

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.

Detailed study of nuclear charge and mass densities. Pt. 1

International Nuclear Information System (INIS)

Berdichevsky, D.; Mosel, U.

1982-01-01

Theoretical and experimental densities are analyzed and compared in detail, in particular in the surface region. For this purpose nuclear size parameters are discussed and new sets of surface parameters are proposed. It is shown that the densities are very close to the error function in the external part of the surface and can be characterized there by two new parameters. For very large r the densities show an exponential behaviour which is analyzed in terms of single-particle density distributions. Furthermore, the effects of the asymmetry, spin-orbit and Coulomb forces on the density distributions are discussed. (orig.)

Many-body theory and Energy Density Functionals

Energy Technology Data Exchange (ETDEWEB)

Baldo, M. [INFN, Catania (Italy)

2016-07-15

In this paper a method is first presented to construct an Energy Density Functional on a microscopic basis. The approach is based on the Kohn-Sham method, where one introduces explicitly the Nuclear Matter Equation of State, which can be obtained by an accurate many-body calculation. In this way it connects the functional to the bare nucleon-nucleon interaction. It is shown that the resulting functional can be performing as the best Gogny force functional. In the second part of the paper it is shown how one can go beyond the mean-field level and the difficulty that can appear. The method is based on the particle-vibration coupling scheme and a formalism is presented that can handle the correct use of the vibrational degrees of freedom within a microscopic approach. (orig.)

Characterizing the Spatial Density Functions of Neural Arbors

Science.gov (United States)

Teeter, Corinne Michelle

Recently, it has been proposed that a universal function describes the way in which all arbors (axons and dendrites) spread their branches over space. Data from fish retinal ganglion cells as well as cortical and hippocampal arbors from mouse, rat, cat, monkey and human provide evidence that all arbor density functions (adf) can be described by a Gaussian function truncated at approximately two standard deviations. A Gaussian density function implies that there is a minimal set of parameters needed to describe an adf: two or three standard deviations (depending on the dimensionality of the arbor) and an amplitude. However, the parameters needed to completely describe an adf could be further constrained by a scaling law found between the product of the standard deviations and the amplitude of the function. In the following document, I examine the scaling law relationship in order to determine the minimal set of parameters needed to describe an adf. First, I find that the at, two-dimensional arbors of fish retinal ganglion cells require only two out of the three fundamental parameters to completely describe their density functions. Second, the three-dimensional, volume filling, cortical arbors require four fundamental parameters: three standard deviations and the total length of an arbor (which corresponds to the amplitude of the function). Next, I characterize the shape of arbors in the context of the fundamental parameters. I show that the parameter distributions of the fish retinal ganglion cells are largely homogenous. In general, axons are bigger and less dense than dendrites; however, they are similarly shaped. The parameter distributions of these two arbor types overlap and, therefore, can only be differentiated from one another probabilistically based on their adfs. Despite artifacts in the cortical arbor data, different types of arbors (apical dendrites, non-apical dendrites, and axons) can generally be differentiated based on their adfs. In addition, within

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.

Density Functional Theory An Advanced Course

CERN Document Server

Dreizler, Reiner M

2011-01-01

Density Functional Theory (DFT) has firmly established itself as the workhorse for the atomic-level simulation of condensed matter phases, pure or composite materials and quantum chemical systems. The present book is a rigorous and detailed introduction to the foundations up to and including such advanced topics as orbital-dependent functionals and both time-dependent and relativistic DFT. Given the many ramifications of contemporary DFT, this text concentrates on the self-contained presentation of the basics of the most widely used DFT variants. This implies a thorough discussion of the corresponding existence theorems and effective single particle equations, as well as of key approximations utilized in implementations. The formal results are complemented by selected quantitative results, which primarily aim at illustrating strengths and weaknesses of a particular approach or functional. DFT for superconducting or nuclear and hadronic systems are not addressed in this work. The structure and material contain...

Derivative discontinuity and exchange-correlation potential of meta-GGAs in density-functional theory.

Science.gov (United States)

Eich, F G; Hellgren, Maria

2014-12-14

We investigate fundamental properties of meta-generalized-gradient approximations (meta-GGAs) to the exchange-correlation energy functional, which have an implicit density dependence via the Kohn-Sham kinetic-energy density. To this purpose, we construct the most simple meta-GGA by expressing the local exchange-correlation energy per particle as a function of a fictitious density, which is obtained by inverting the Thomas-Fermi kinetic-energy functional. This simple functional considerably improves the total energy of atoms as compared to the standard local density approximation. The corresponding exchange-correlation potentials are then determined exactly through a solution of the optimized effective potential equation. These potentials support an additional bound state and exhibit a derivative discontinuity at integer particle numbers. We further demonstrate that through the kinetic-energy density any meta-GGA incorporates a derivative discontinuity. However, we also find that for commonly used meta-GGAs the discontinuity is largely underestimated and in some cases even negative.

Derivative discontinuity and exchange-correlation potential of meta-GGAs in density-functional theory

International Nuclear Information System (INIS)

Eich, F. G.; Hellgren, Maria

2014-01-01

We investigate fundamental properties of meta-generalized-gradient approximations (meta-GGAs) to the exchange-correlation energy functional, which have an implicit density dependence via the Kohn-Sham kinetic-energy density. To this purpose, we construct the most simple meta-GGA by expressing the local exchange-correlation energy per particle as a function of a fictitious density, which is obtained by inverting the Thomas-Fermi kinetic-energy functional. This simple functional considerably improves the total energy of atoms as compared to the standard local density approximation. The corresponding exchange-correlation potentials are then determined exactly through a solution of the optimized effective potential equation. These potentials support an additional bound state and exhibit a derivative discontinuity at integer particle numbers. We further demonstrate that through the kinetic-energy density any meta-GGA incorporates a derivative discontinuity. However, we also find that for commonly used meta-GGAs the discontinuity is largely underestimated and in some cases even negative

Interpretation of the U L3-edge EXAFS in uranium dioxide using molecular dynamics and density functional theory simulations

International Nuclear Information System (INIS)

Bocharov, Dmitry; Chollet, Melanie; Krack, Matthias; Bertsch, Johannes; Grolimund, Daniel; Martin, Matthias; Kuzmin, Alexei; Purans, Juris; Kotomin, Eugene

2016-01-01

X-ray absorption spectroscopy is employed to study the local structure of pure and Cr-doped UO 2 at 300 K. The U L 3 -edge EXAFS spectrum is interpreted within the multiplescattering (MS) theory using the results of the classical and ab initio molecular dynamics simulations, allowing us to validate the accuracy of theoretical models. The Cr K-edge XANES is simulated within the full-multiple-scattering formalism considering a substitutional model (Cr at U site). It is shown that both unrelaxed and relaxed structures, produced by ab initio density functional theory (DFT) calculations, fail to describe the experiment. (paper)

Density functional theory based molecular dynamics study of hydration and electronic properties of aqueous La(3+).

Science.gov (United States)

Terrier, Cyril; Vitorge, Pierre; Gaigeot, Marie-Pierre; Spezia, Riccardo; Vuilleumier, Rodolphe

2010-07-28

Structural and electronic properties of La(3+) immersed in bulk water have been assessed by means of density functional theory (DFT)-based Car-Parrinello molecular dynamics (CPMD) simulations. Correct structural properties, i.e., La(III)-water distances and La(III) coordination number, can be obtained within the framework of Car-Parrinello simulations providing that both the La pseudopotential and conditions of the dynamics (fictitious mass and time step) are carefully set up. DFT-MD explicitly treats electronic densities and is shown here to provide a theoretical justification to the necessity of including polarization when studying highly charged cations such as lanthanoids(III) with classical MD. La(3+) was found to strongly polarize the water molecules located in the first shell, giving rise to dipole moments about 0.5 D larger than those of bulk water molecules. Finally, analyzing Kohn-Sham orbitals, we found La(3+) empty 4f orbitals extremely compact and to a great extent uncoupled from the water conduction band, while the 5d empty orbitals exhibit mixing with unoccupied states of water.

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)

Geometry optimization of molecules within an LCGTO local-density functional approach

International Nuclear Information System (INIS)

Mintmire, J.W.

1990-01-01

We describe our implementation of geometry optimization techniques within the linear combination of Gaussian-type orbitals (LCGTO) approach to local-density functional theory. The algorithm for geometry optimization is based on the evaluation of the gradient of the total energy with respect to internal coordinates within the local-density functional scheme. We present optimization results for a range of small molecules which serve as test cases for our approach

Structural flexibility of 2-hetaryl chromium aminocarbene complexes: Experimental and theoretical evidence

Czech Academy of Sciences Publication Activity Database

Kvapilová, Hana; Eigner, V.; Hoskovcová, I.; Tobrman, T.; Čejka, J.; Záliš, Stanislav

2014-01-01

Roč. 421, SEP 2014 (2014), s. 439-445 ISSN 0020-1693 R&D Projects: GA MŠk LD14129 Institutional support: RVO:61388955 Keywords : Transition metal complex * Density functional theory * Potential energy surface Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.046, year: 2014

Determination of Charge-Carrier Mobility in Disordered Thin-Film Solar Cells as a Function of Current Density

Science.gov (United States)

Mäckel, Helmut; MacKenzie, Roderick C. I.

2018-03-01

Charge-carrier mobility is a fundamental material parameter, which plays an important role in determining solar-cell efficiency. The higher the mobility, the less time a charge carrier will spend in a device and the less likely it is that it will be lost to recombination. Despite the importance of this physical property, it is notoriously difficult to measure accurately in disordered thin-film solar cells under operating conditions. We, therefore, investigate a method previously proposed in the literature for the determination of mobility as a function of current density. The method is based on a simple analytical model that relates the mobility to carrier density and transport resistance. By revising the theoretical background of the method, we clearly demonstrate what type of mobility can be extracted (constant mobility or effective mobility of electrons and holes). We generalize the method to any combination of measurements that is able to determine the mean electron and hole carrier density, and the transport resistance at a given current density. We explore the robustness of the method by simulating typical organic solar-cell structures with a variety of physical properties, including unbalanced mobilities, unbalanced carrier densities, and for high or low carrier trapping rates. The simulations reveal that near VOC and JSC , the method fails due to the limitation of determining the transport resistance. However, away from these regions (and, importantly, around the maximum power point), the method can accurately determine charge-carrier mobility. In the presence of strong carrier trapping, the method overestimates the effective mobility due to an underestimation of the carrier density.

Density-functional theory based on the electron distribution on the energy coordinate

Science.gov (United States)

Takahashi, Hideaki

2018-03-01

We developed an electronic density functional theory utilizing a novel electron distribution n(ɛ) as a basic variable to compute ground state energy of a system. n(ɛ) is obtained by projecting the electron density n({\\boldsymbol{r}}) defined on the space coordinate {\\boldsymbol{r}} onto the energy coordinate ɛ specified with the external potential {\\upsilon }ext}({\\boldsymbol{r}}) of interest. It was demonstrated that the Kohn-Sham equation can also be formulated with the exchange-correlation functional E xc[n(ɛ)] that employs the density n(ɛ) as an argument. It turned out an exchange functional proposed in our preliminary development suffices to describe properly the potential energies of several types of chemical bonds with comparable accuracies to the corresponding functional based on local density approximation. As a remarkable feature of the distribution n(ɛ) it inherently involves the spatially non-local information of the exchange hole at the bond dissociation limit in contrast to conventional approximate functionals. By taking advantage of this property we also developed a prototype of the static correlation functional E sc including no empirical parameters, which showed marked improvements in describing the dissociations of covalent bonds in {{{H}}}2,{{{C}}}2{{{H}}}4 and {CH}}4 molecules.

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.

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.

Hartree and Exchange in Ensemble Density Functional Theory: Avoiding the Nonuniqueness Disaster.

Science.gov (United States)

Gould, Tim; Pittalis, Stefano

2017-12-15

Ensemble density functional theory is a promising method for the efficient and accurate calculation of excitations of quantum systems, at least if useful functionals can be developed to broaden its domain of practical applicability. Here, we introduce a guaranteed single-valued "Hartree-exchange" ensemble density functional, E_{Hx}[n], in terms of the right derivative of the universal ensemble density functional with respect to the coupling constant at vanishing interaction. We show that E_{Hx}[n] is straightforwardly expressible using block eigenvalues of a simple matrix [Eq. (14)]. Specialized expressions for E_{Hx}[n] from the literature, including those involving superpositions of Slater determinants, can now be regarded as originating from the unifying picture presented here. We thus establish a clear and practical description for Hartree and exchange in ensemble systems.

Breaking the theoretical scaling limit for predicting quasiparticle energies: the stochastic GW approach.

Science.gov (United States)

Neuhauser, Daniel; Gao, Yi; Arntsen, Christopher; Karshenas, Cyrus; Rabani, Eran; Baer, Roi

2014-08-15

We develop a formalism to calculate the quasiparticle energy within the GW many-body perturbation correction to the density functional theory. The occupied and virtual orbitals of the Kohn-Sham Hamiltonian are replaced by stochastic orbitals used to evaluate the Green function G, the polarization potential W, and, thereby, the GW self-energy. The stochastic GW (sGW) formalism relies on novel theoretical concepts such as stochastic time-dependent Hartree propagation, stochastic matrix compression, and spatial or temporal stochastic decoupling techniques. Beyond the theoretical interest, the formalism enables linear scaling GW calculations breaking the theoretical scaling limit for GW as well as circumventing the need for energy cutoff approximations. We illustrate the method for silicon nanocrystals of varying sizes with N_{e}>3000 electrons.

A Density Functional Theory Study

KAUST Repository

Lim, XiaoZhi

2011-12-11

Complexes with pincer ligand moieties have garnered much attention in the past few decades. They have been shown to be highly active catalysts in several known transition metal-catalyzed organic reactions as well as some unprecedented organic transformations. At the same time, the use of computational organometallic chemistry to aid in the understanding of the mechanisms in organometallic catalysis for the development of improved catalysts is on the rise. While it was common in earlier studies to reduce computational cost by truncating donor group substituents on complexes such as tertbutyl or isopropyl groups to hydrogen or methyl groups, recent advancements in the processing capabilities of computer clusters and codes have streamlined the time required for calculations. As the full modeling of complexes become increasingly popular, a commonly overlooked aspect, especially in the case of complexes bearing isopropyl substituents, is the conformational analysis of complexes. Isopropyl groups generate a different conformer with each 120 ° rotation (rotamer), and it has been found that each rotamer typically resides in its own potential energy well in density functional theory studies. As a result, it can be challenging to select the most appropriate structure for a theoretical study, as the adjustment of isopropyl substituents from a higher-energy rotamer to the lowest-energy rotamer usually does not occur during structure optimization. In this report, the influence of the arrangement of isopropyl substituents in pincer complexes on calculated complex structure energies as well as a case study on the mechanism of the isomerization of an iPrPCP-Fe complex is covered. It was found that as many as 324 rotamers can be generated for a single complex, as in the case of an iPrPCP-Ni formato complex, with the energy difference between the global minimum and the highest local minimum being as large as 16.5 kcalmol-1. In the isomerization of a iPrPCP-Fe complex, it was found

Artificial cognitive memory—changing from density driven to functionality driven

Science.gov (United States)

Shi, L. P.; Yi, K. J.; Ramanathan, K.; Zhao, R.; Ning, N.; Ding, D.; Chong, T. C.

2011-03-01

Increasing density based on bit size reduction is currently a main driving force for the development of data storage technologies. However, it is expected that all of the current available storage technologies might approach their physical limits in around 15 to 20 years due to miniaturization. To further advance the storage technologies, it is required to explore a new development trend that is different from density driven. One possible direction is to derive insights from biological counterparts. Unlike physical memories that have a single function of data storage, human memory is versatile. It contributes to functions of data storage, information processing, and most importantly, cognitive functions such as adaptation, learning, perception, knowledge generation, etc. In this paper, a brief review of current data storage technologies are presented, followed by discussions of future storage technology development trend. We expect that the driving force will evolve from density to functionality, and new memory modules associated with additional functions other than only data storage will appear. As an initial step toward building a future generation memory technology, we propose Artificial Cognitive Memory (ACM), a memory based intelligent system. We also present the characteristics of ACM, new technologies that can be used to develop ACM components such as bioinspired element cells (silicon, memristor, phase change, etc.), and possible methodologies to construct a biologically inspired hierarchical system.

Orbital-dependent exchange-correlation functionals in density-functional theory realized by the FLAPW method

Energy Technology Data Exchange (ETDEWEB)

Betzinger, Markus

2011-12-14

In this thesis, we extended the applicability of the full-potential linearized augmented-plane-wave (FLAPW) method, one of the most precise, versatile and generally applicable electronic structure methods for solids working within the framework of density-functional theory (DFT), to orbital-dependent functionals for the exchange-correlation (xc) energy. Two different schemes that deal with orbital-dependent functionals, the Kohn-Sham (KS) and the generalized Kohn-Sham (gKS) formalism, have been realized. Hybrid functionals, combining some amount of the orbital-dependent exact exchange energy with local or semi-local functionals of the density, are implemented within the gKS scheme. We work in particular with the PBE0 hybrid of Perdew, Burke, and Ernzerhof. Our implementation relies on a representation of the non-local exact exchange potential - its calculation constitutes the most time consuming step in a practical calculation - by an auxiliary mixed product basis (MPB). In this way, the matrix elements of the Hamiltonian corresponding to the non-local potential become a Brillouin-zone (BZ) sum over vector-matrix-vector products. Several techniques are developed and explored to further accelerate our numerical scheme. We show PBE0 results for a variety of semiconductors and insulators. In comparison with experiment, the PBE0 functional leads to improved band gaps and an improved description of localized states. Even for the ferromagnetic semiconductor EuO with localized 4f electrons, the electronic and magnetic properties are correctly described by the PBE0 functional. Subsequently, we discuss the construction of the local, multiplicative exact exchange (EXX) potential from the non-local, orbital-dependent exact exchange energy. For this purpose we employ the optimized effective potential (OEP) method. Central ingredients of the OEP equation are the KS wave-function response and the single-particle density response function. We show that a balance between the LAPW

Orbital-dependent exchange-correlation functionals in density-functional theory realized by the FLAPW method

International Nuclear Information System (INIS)

Betzinger, Markus

2011-01-01

In this thesis, we extended the applicability of the full-potential linearized augmented-plane-wave (FLAPW) method, one of the most precise, versatile and generally applicable electronic structure methods for solids working within the framework of density-functional theory (DFT), to orbital-dependent functionals for the exchange-correlation (xc) energy. Two different schemes that deal with orbital-dependent functionals, the Kohn-Sham (KS) and the generalized Kohn-Sham (gKS) formalism, have been realized. Hybrid functionals, combining some amount of the orbital-dependent exact exchange energy with local or semi-local functionals of the density, are implemented within the gKS scheme. We work in particular with the PBE0 hybrid of Perdew, Burke, and Ernzerhof. Our implementation relies on a representation of the non-local exact exchange potential - its calculation constitutes the most time consuming step in a practical calculation - by an auxiliary mixed product basis (MPB). In this way, the matrix elements of the Hamiltonian corresponding to the non-local potential become a Brillouin-zone (BZ) sum over vector-matrix-vector products. Several techniques are developed and explored to further accelerate our numerical scheme. We show PBE0 results for a variety of semiconductors and insulators. In comparison with experiment, the PBE0 functional leads to improved band gaps and an improved description of localized states. Even for the ferromagnetic semiconductor EuO with localized 4f electrons, the electronic and magnetic properties are correctly described by the PBE0 functional. Subsequently, we discuss the construction of the local, multiplicative exact exchange (EXX) potential from the non-local, orbital-dependent exact exchange energy. For this purpose we employ the optimized effective potential (OEP) method. Central ingredients of the OEP equation are the KS wave-function response and the single-particle density response function. We show that a balance between the LAPW

Optical Absorption in Molecular Crystals from Time-Dependent Density Functional Theory

Science.gov (United States)

2017-04-23

Our approach represents a full solid-state calculation, allowing for polarization ef- fects while still capable of capturing inter-molecular dis...AFRL-AFOSR-UK-TR-2017-0030 Optical absorption in molecular crystals from time-dependent density functional theory Leeor Kronik WEIZMANN INSTITUTE OF...from time-dependent density functional theory 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA9550-15-1-0290 5c.  PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S

Electronic and thermoelectric properties of InN studied using ab initio density functional theory and Boltzmann transport calculations

Energy Technology Data Exchange (ETDEWEB)

Borges, P. D., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu; Scolfaro, L., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu [Department of Physics, Texas State University, San Marcos, Texas 78666 (United States)

2014-12-14

The thermoelectric properties of indium nitride in the most stable wurtzite phase (w-InN) as a function of electron and hole concentrations and temperature were studied by solving the semiclassical Boltzmann transport equations in conjunction with ab initio electronic structure calculations, within Density Functional Theory. Based on maximally localized Wannier function basis set and the ab initio band energies, results for the Seebeck coefficient are presented and compared with available experimental data for n-type as well as p-type systems. Also, theoretical results for electric conductivity and power factor are presented. Most cases showed good agreement between the calculated properties and experimental data for w-InN unintentionally and p-type doped with magnesium. Our predictions for temperature and concentration dependences of electrical conductivity and power factor revealed a promising use of InN for intermediate and high temperature thermoelectric applications. The rigid band approach and constant scattering time approximation were utilized in the calculations.

Diffusion of hydrogen into and through γ-iron by density functional theory

Science.gov (United States)

Chohan, Urslaan K.; Koehler, Sven P. K.; Jimenez-Melero, Enrique

2018-06-01

This study is concerned with the early stages of hydrogen embrittlement on an atomistic scale. We employed density functional theory to investigate hydrogen diffusion through the (100), (110) and (111) surfaces of γ-Fe. The preferred adsorption sites and respective energies for hydrogen adsorption were established for each plane, as well as a minimum energy pathway for diffusion. The H atoms adsorb on the (100), (110) and (111) surfaces with energies of ∼4.06 eV, ∼3.92 eV and ∼4.05 eV, respectively. The barriers for bulk-like diffusion for the (100), (110) and (111) surfaces are ∼0.6 eV, ∼0.5 eV and ∼0.7 eV, respectively. We compared these calculated barriers with previously obtained experimental data in an Arrhenius plot, which indicates good agreement between experimentally measured and theoretically predicted activation energies. Texturing austenitic steels such that the (111) surfaces of grains are preferentially exposed at the cleavage planes may be a possibility to reduce hydrogen embrittlement.

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.

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.

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.

Synergy between pair coupled cluster doubles and pair density functional theory

Energy Technology Data Exchange (ETDEWEB)

Garza, Alejandro J.; Bulik, Ireneusz W. [Department of Chemistry, Rice University, Houston, Texas 77251-1892 (United States); Henderson, Thomas M. [Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892 (United States); Scuseria, Gustavo E. [Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892 (United States); Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)

2015-01-28

Pair coupled cluster doubles (pCCD) has been recently studied as a method capable of accounting for static correlation with low polynomial cost. We present three combinations of pCCD with Kohn–Sham functionals of the density and on-top pair density (the probability of finding two electrons on top of each other) to add dynamic correlation to pCCD without double counting. With a negligible increase in computational cost, these pCCD+DFT blends greatly improve upon pCCD in the description of typical problems where static and dynamic correlations are both important. We argue that—as a black-box method with low scaling, size-extensivity, size-consistency, and a simple quasidiagonal two-particle density matrix—pCCD is an excellent match for pair density functionals in this type of fusion of multireference wavefunctions with DFT.

Benchmarking Density Functionals for Chemical Bonds of Gold

DEFF Research Database (Denmark)

Kepp, Kasper Planeta

2017-01-01

Gold plays a major role in nanochemistry, catalysis, and electrochemistry. Accordingly, hundreds of studies apply density functionals to study chemical bonding with gold, yet there is no systematic attempt to assess the accuracy of these methods applied to gold. This paper reports a benchmark aga...

Dark matter and gas density profiles - a consequence of entropy bifurcation

International Nuclear Information System (INIS)

Leubner, M. P.

2006-01-01

The radial profiles of dark matter and hot plasma density distributions of relaxed galaxies and clusters were hitherto commonly fitted by empirical functions. On the other hand, the fundamental concept of non-extensive statistics accounts for long-range interactions and correlations present in gravitationally coupled ensembles and plasmas. We provide a theoretical link of non-extensive statistics to large scale astrophysical structures and show that the underlying tandem character of the entropy results in a bifurcation of the density distribution. A kinetic dark matter and thermodynamic gas branch turn out as natural consequence within the theory and is controlled by one single parameter, measuring physically the degree of correlations in the system. The theoretically derived density profiles are shown to represent accurately the characteristics of both, DM and hot plasma distributions, as observed or generated in N-body and hydro-simulations. The significant advantage over empirical fitting functions is provided by the physical content of the non-extensive approach wherefore it is proposed to model observed density profiles of astrophysical structures within the fundamental context of entropy generalization, accounting for nonlocality and long-range interactions in gravitationally coupled systems

Wigner Function of Density Operator for Negative Binomial Distribution

International Nuclear Information System (INIS)

Xu Xinglei; Li Hongqi

2008-01-01

By using the technique of integration within an ordered product (IWOP) of operator we derive Wigner function of density operator for negative binomial distribution of radiation field in the mixed state case, then we derive the Wigner function of squeezed number state, which yields negative binomial distribution by virtue of the entangled state representation and the entangled Wigner operator

Approximate self-consistent potentials for density-functional-theory exchange-correlation functionals

International Nuclear Information System (INIS)

Cafiero, Mauricio; Gonzalez, Carlos

2005-01-01

We show that potentials for exchange-correlation functionals within the Kohn-Sham density-functional-theory framework may be written as potentials for simpler functionals multiplied by a factor close to unity, and in a self-consistent field calculation, these effective potentials find the correct self-consistent solutions. This simple theory is demonstrated with self-consistent exchange-only calculations of the atomization energies of some small molecules using the Perdew-Kurth-Zupan-Blaha (PKZB) meta-generalized-gradient-approximation (meta-GGA) exchange functional. The atomization energies obtained with our method agree with or surpass previous meta-GGA calculations performed in a non-self-consistent manner. The results of this work suggest the utility of this simple theory to approximate exchange-correlation potentials corresponding to energy functionals too complicated to generate closed forms for their potentials. We hope that this method will encourage the development of complex functionals which have correct boundary conditions and are free of self-interaction errors without the worry that the functionals are too complex to differentiate to obtain potentials

Solvation Mechanism of Task-Specific Ionic Liquids in Water: A Combined Investigation Using Classical Molecular Dynamics and Density Functional Theory.

Science.gov (United States)

Yuvaraj, Surya V J; Zhdanov, Ravil K; Belosludov, Rodion V; Belosludov, Vladimir R; Subbotin, Oleg S; Kanie, Kiyoshi; Funaki, Kenji; Muramatsu, Atsushi; Nakamura, Takashi; Kawazoe, Yoshiyuki

2015-10-08

The solvation behavior of task-specific ionic liquids (TSILs) containing a common, L-histidine derived imidazolium cation [C20H28N3O3](+) and different anions, bromide-[Br](-) and bis(trifluoromethylsulfonyl)amide-[NTF2](-), in water is examined, computationally. These amino acid functionalized ionic liquids (ILs) are taken into account because of their ability to react with rare earth metal salts. It has been noted that the TSIL with [Br](-) is more soluble than its counterpart TSIL with [NTF2](-), experimentally. In this theoretical work, the combined classical molecular dynamics (CMD) and density functional theory (DFT) calculations are performed to study the behavior of the bulk phase of these two TSILs in the vicinity of water (H2O) molecules with different concentrations. Initially, all the constructed systems are equilibrated using the CMD method. The final structures of the equilibrated systems are extracted for DFT calculations. Under CMD operation, the radial distribution function (RDF) plots and viscosity of TSILs are analyzed to understand the effect of water on TSILs. In the DFT regime, binding energy per H2O, charge transfer, charge density mapping, and electronic density of states (EDOS) analyses are done. The CMD results along with the DFT results are consolidated to support the hydrophilic and hydrophobic nature of the TSILs. Interestingly, we have found a strong correlation between the viscosity and the EDOS results that leads to an understanding of the hydration properties of the TSILs.

INTERACTIVE VISUALIZATION OF PROBABILITY AND CUMULATIVE DENSITY FUNCTIONS

KAUST Repository

Potter, Kristin; Kirby, Robert Michael; Xiu, Dongbin; Johnson, Chris R.

2012-01-01

The probability density function (PDF), and its corresponding cumulative density function (CDF), provide direct statistical insight into the characterization of a random process or field. Typically displayed as a histogram, one can infer probabilities of the occurrence of particular events. When examining a field over some two-dimensional domain in which at each point a PDF of the function values is available, it is challenging to assess the global (stochastic) features present within the field. In this paper, we present a visualization system that allows the user to examine two-dimensional data sets in which PDF (or CDF) information is available at any position within the domain. The tool provides a contour display showing the normed difference between the PDFs and an ansatz PDF selected by the user and, furthermore, allows the user to interactively examine the PDF at any particular position. Canonical examples of the tool are provided to help guide the reader into the mapping of stochastic information to visual cues along with a description of the use of the tool for examining data generated from an uncertainty quantification exercise accomplished within the field of electrophysiology.

Path integrals for electronic densities, reactivity indices, and localization functions in quantum systems.

Science.gov (United States)

Putz, Mihai V

2009-11-10

The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr's quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions - all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems.

Path Integrals for Electronic Densities, Reactivity Indices, and Localization Functions in Quantum Systems

Directory of Open Access Journals (Sweden)

Mihai V. Putz

2009-11-01

Full Text Available The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving many-electronic systems.

Pressure and surface tension of solid-liquid interface using Tara zona density functional theory

International Nuclear Information System (INIS)

Moradi, M.; Kavosh Tehrani, M.

2001-01-01

The weighted density functional theory proposed by Tara zona is applied to study the solid-liquid interface. In the last two decades the weighted density functional became a useful tool to consider the properties of inhomogeneous liquids. In this theory, the role of the size of molecules or the particles of which the matter is composed, was found to be important. In this research we study a hard sphere fluid beside a hard wall. For this study the liquid is an inhomogeneous system. We use the definition of the direct correlation function as a second derivative of free energy with respect to the density. We use this definition and the definition of the weighting function, then we minimize the grand potential with respect to the density to get the Euler Lagrange equation and we obtain an integral equation to find the inhomogeneous density profile. The obtained density profile as a function of the distance from the wall, for different bulk density is pitted in three dimensions. We also calculate the pressure and compare it with the Carnahan-Starling results, and finally we obtained the surface tension at liquid-solid interface and compared it with the results of Monte Carlo simulation

New Methods of Esterification of Nanodiamonds in Fighting Breast Cancer—A Density Functional Theory Approach

Directory of Open Access Journals (Sweden)

Linda-Lucila Landeros-Martinez

2017-10-01

Full Text Available The use of nanodiamonds as anticancer drug delivery vehicles has received much attention in recent years. In this theoretical paper, we propose using different esterification methods for nanodiamonds. The monomers proposed are 2-hydroxypropanal, polyethylene glycol, and polyglicolic acid. Specifically, the hydrogen bonds, infrared (IR spectra, molecular polar surface area, and reactivity parameters are analyzed. The monomers proposed for use in esterification follow Lipinski’s rule of five, meaning permeability is good, they have good permeation, and their bioactivity is high. The results show that the complex formed between tamoxifen and nanodiamond esterified with polyglicolic acid presents the greatest number of hydrogen bonds and a good amount of molecular polar surface area. Calculations concerning the esterified nanodiamond and reactivity parameters were performed using Density Functional Theory with the M06 functional and the basis set 6–31G (d; for the esterified nanodiamond–Tamoxifen complexes, the semi-empirical method PM6 was used. The solvent effect has been taken into account by using implicit modelling and the conductor-like polarizable continuum model.

Efficient Estimation of Dynamic Density Functions with Applications in Streaming Data