De Almeida, Wagner B.
2000-01-01
The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can ma...
International Nuclear Information System (INIS)
Almeida, Wagner B. de
2000-01-01
The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase an initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions. (author)
Quantum chemistry the development of ab initio methods in molecular electronic structure theory
Schaefer III, Henry F
2004-01-01
This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi
Ab-initio electronic band structure calculations for beryllium chalcogenides
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Kalpana, G.; Pari, G.; Yousuf, Mohammad
1997-01-01
The first principle tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties, structural phase transition and pressure dependence of band gap of BeS, BeSe and BeTe. We have calculated the energy-volume relations for these compounds in the B3 and B8 phases. The calculated lattice parameters, bulk modulus and the pressure-volume relation were found to be in good agreement with the recent experimental results. The calculated B3→B8 structural transition pressure for BeS, BeSe and BeTe agree well with the recent experimental results. Our calculations show that these compounds are indirect band gap (Γ-X) semiconductors at ambient conditions. The calculated band gap values are found to be underestimated by 20-30% which is due to the usage of LDA. After the structural transition to the B8 phase, BeS continues to be indirect band gap semiconductors and ultimately above 100 GPa it metallises, BeSe and BeTe are metallic at the B3→B8 structural transition. (author)
International Nuclear Information System (INIS)
Degoli, Elena; Bisi, O.; Ossicini, Stefano; Cantele, G.; Ninno, D.; Luppi, Eleonora; Magri, Rita
2004-01-01
Electronic and structural properties of small hydrogenated silicon nanoclusters as a function of dimension are calculated from ab initio technique. The effects induced by the creation of an electron-hole pair are discussed in detail, showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure after an electronic excitation of the cluster is analyzed together with the role of the symmetry constraint during the relaxation. We point out how the overall effect is that of significantly changing the electronic spectrum if no symmetry constraint is imposed to the system. Such distortion can account for the Stokes shift and provides a possible structural model to be linked to the four-level scheme invoked in the literature to explain recent results for the optical gain in silicon nanoclusters. Finally, formation energies for clusters with increasing dimension are calculated and their relative stability discussed
The role of ab initio electronic structure calculations in studies of the strength of materials
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Sob, M.; Friak, M.; Legut, D.; Fiala, J.; Vitek, V.
2004-01-01
In this paper we give an account of applications of quantum-mechanical (first-principles) electronic structure calculations to the problem of theoretical tensile strength in metals and intermetallics. First, we review previous as well as ongoing research on this subject. We then describe briefly the electronic structure calculational methods and simulation of the tensile test. This approach is then illustrated by calculations of theoretical tensile strength in iron and in the intermetallic compound Ni 3 Al. The anisotropy of calculated tensile strength is explained in terms of higher-symmetry structures encountered along the deformation paths studied. The table summarizing values of theoretical tensile strengths calculated up to now is presented and the role of ab initio electronic structure calculations in contemporary studies of the strength of material is discussed
DEFF Research Database (Denmark)
Gorelik, Tatiana E; van de Streek, Jacco; Kilbinger, Andreas F M
2012-01-01
Ab-initio crystal structure analysis of organic materials from electron diffraction data is presented. The data were collected using the automated electron diffraction tomography (ADT) technique. The structure solution and refinement route is first validated on the basis of the known crystal stru...
Ab Initio Calculations of the Electronic Structures and Biological Functions of Protein Molecules
Zheng, Haoping
2003-04-01
The self-consistent cluster-embedding (SCCE) calculation method reduces the computational effort from M3 to about M1 (M is the number of atoms in the system) with unchanged calculation precision. So the ab initio, all-electron calculation of the electronic structure and biological function of protein molecule becomes a reality, which will promote new proteomics considerably. The calculated results of two real protein molecules, the trypsin inhibitor from the seeds of squash Cucurbita maxima (CMTI-I, 436 atoms) and the Ascaris trypsin inhibitor (912 atoms, two three-dimensional structures), are presented. The reactive sites of the inhibitors are determined and explained. The precision of structure determination of inhibitors are tested theoretically.
International Nuclear Information System (INIS)
Klevets, Ivan; Bryk, Taras
2014-01-01
Electron-ion structure factors, calculated in ab initio molecular dynamics simulations, are reported for several binary liquids with different kinds of chemical bonding: metallic liquid alloy Bi–Pb, molten salt RbF, and liquid water. We derive analytical expressions for the long-wavelength asymptotes of the partial electron-ion structure factors of binary systems and show that the analytical results are in good agreement with the ab initio simulation data. The long-wavelength behaviour of the total charge structure factors for the three binary liquids is discussed
Hoy, Erik P; Mazziotti, David A
2015-08-14
Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory.
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Hoy, Erik P.; Mazziotti, David A., E-mail: damazz@uchicago.edu [Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)
2015-08-14
Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory.
Giovannetti, G.; Brocks, G.; van den Brink, J.
2008-01-01
We investigate the effect that potassium intercalation has on the electronic structure of copper phthalocyanine (CuPc) molecular crystals by means of ab initio density functional calculations. Pristine CuPc (in its alpha and beta structures) is found to be an insulator containing local magnetic
Moradian, Rostam; Behzad, Somayeh; Chegel, Raad
2008-10-01
By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius.
International Nuclear Information System (INIS)
Moradian, Rostam; Behzad, Somayeh; Chegel, Raad
2008-01-01
By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius
Ab initio calculations of the electronic structure and bonding characteristics of LaB6
International Nuclear Information System (INIS)
Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.
2005-01-01
Lanthanum hexaboride (LaB 6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB 6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB 6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB 6 system and partially explains its high efficiency as a thermionic emitter
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Tomic, Milan
2013-07-01
The ab-initio molecular dynamics framework has been the cornerstone of computational solid state physics in the last few decades. Although it is already a mature field it is still rapidly developing to accommodate the growth in solid state research as well as to efficiently utilize the increase in computing power. Starting from the first principles, the ab-initio molecular dynamics provides essential information about structural and electronic properties of matter under various external conditions. In this thesis we use the ab-initio molecular dynamics to study the behavior of BaFe{sub 2}As{sub 2} and CaFe{sub 2}As{sub 2} under the application of external pressure. BaFe{sub 2}As{sub 2} and CaFe{sub 2}As{sub 2} belong to the family of iron based superconductors which are a novel and promising superconducting materials. The application of pressure is one of two key methods by which electronic and structural properties of iron based superconductors can be modified, the other one being doping (or chemical pressure). In particular, it has been noted that pressure conditions have an important effect, but their exact role is not fully understood. To better understand the effect of different pressure conditions we have performed a series of ab-initio simulations of pressure application. In order to apply the pressure with arbitrary stress tensor we have developed a method based on the Fast Inertial Relaxation Engine, whereby the unit cell and the atomic positions are evolved according to the metadynamical equations of motion. We have found that the application of hydrostatic and c axis uniaxial pressure induces a phase transition from the magnetically ordered orthorhombic phase to the non-magnetic collapsed tetragonal phase in both BaFe{sub 2}As{sub 2} and CaFe{sub 2}As{sub 2}. In the case of BaFe{sub 2}As{sub 2}, an intermediate tetragonal non-magnetic tetragonal phase is observed in addition. Application of the uniaxial pressure parallel to the c axis reduces the
International Nuclear Information System (INIS)
Tomic, Milan
2013-01-01
The ab-initio molecular dynamics framework has been the cornerstone of computational solid state physics in the last few decades. Although it is already a mature field it is still rapidly developing to accommodate the growth in solid state research as well as to efficiently utilize the increase in computing power. Starting from the first principles, the ab-initio molecular dynamics provides essential information about structural and electronic properties of matter under various external conditions. In this thesis we use the ab-initio molecular dynamics to study the behavior of BaFe 2 As 2 and CaFe 2 As 2 under the application of external pressure. BaFe 2 As 2 and CaFe 2 As 2 belong to the family of iron based superconductors which are a novel and promising superconducting materials. The application of pressure is one of two key methods by which electronic and structural properties of iron based superconductors can be modified, the other one being doping (or chemical pressure). In particular, it has been noted that pressure conditions have an important effect, but their exact role is not fully understood. To better understand the effect of different pressure conditions we have performed a series of ab-initio simulations of pressure application. In order to apply the pressure with arbitrary stress tensor we have developed a method based on the Fast Inertial Relaxation Engine, whereby the unit cell and the atomic positions are evolved according to the metadynamical equations of motion. We have found that the application of hydrostatic and c axis uniaxial pressure induces a phase transition from the magnetically ordered orthorhombic phase to the non-magnetic collapsed tetragonal phase in both BaFe 2 As 2 and CaFe 2 As 2 . In the case of BaFe 2 As 2 , an intermediate tetragonal non-magnetic tetragonal phase is observed in addition. Application of the uniaxial pressure parallel to the c axis reduces the critical pressure of the phase transition by an order of magnitude
Moradian, Rostam; Behzad, Somayeh; Chegel, Raad
2009-12-01
By using ab initio density functional theory, the structural and electronic properties of (n,n)@(11,11) double-walled silicon carbide nanotubes (SiCNTs) are investigated. Our calculations reveal the existence of an energetically favorable double-walled nanotube whose interwall distance is about 4.3 Å. Interwall spacing and curvature difference are found to be essential for the electronic states around the Fermi level.
Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations
Directory of Open Access Journals (Sweden)
Hamsa Naji Nasir
2012-01-01
Full Text Available Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces energy gap.
International Nuclear Information System (INIS)
Demchenko, I.N.; Chernyshova, M.; Stolte, W.C.; Speaks, D.T.; Derkachova, A.
2012-01-01
The electronic structure of cadmium dichloride has been studied by X-ray absorption near edge structure (XANES) and, for the first time, by resonant inelastic X-ray scattering (RIXS) at the Cl K edge. Good agreement was obtained between the non-resonant X-ray emission (XES) along with XANES experimental spectra and the calculated Cl 3p local partial density of states (DOS). The calculations were performed using the full-potential linearized-augmented-plane-wave with the local orbitals (FP-(L)APW l o) method utilized in the WIEN2k code. It was shown that the position of the RIXS band in CdCl 2 follows a linear dispersion according to the Raman–Stokes law if the excitation energy is tuned below the absorption threshold. The situation changes for core excitation above the photoabsorption threshold where the dispersion relation is split into two branches. The position of the resonant contribution does not depend on the excitation energy, while the excitonic sideband follows the Raman–Stoke law. Combined XANES and RIXS measurements compared to calculated band structure allowed us to determine the direct band gap of CdCl 2 to be at 5.7 ± 0.05 eV. -- Highlights: ► XANES at the K edge of Cl and related emission KV band interpreted within the ab initio DFT formalism. ► Two dominant contributions observed in RIXS data: the resonant and the excitonic ones. ► The dispersion relation below the absorption threshold follows Raman–Stokes law. ► Dispersion above the threshold splits into two qualitatively different relations. ► Overlapping of XAS spectrum with RIXS one makes possible to estimate direct band gap value to be 5.7 eV.
International Nuclear Information System (INIS)
Iori, Federico; Degoli, Elena; Luppi, Eleonora; Magri, Rita; Marri, Ivan; Cantele, G.; Ninno, D.; Trani, F.; Ossicini, Stefano
2006-01-01
There are experimental evidences that doping control at the nanoscale can significantly modify the optical properties with respect to the pure systems. This is the case of silicon nanocrystals (Si-nc), for which it has been shown that the photoluminescence (PL) peak can be tuned also below the bulk Si band gap by properly controlling the impurities, for example by boron (B) and phosphorus (P) codoping. In this work, we report on an ab initio study of impurity states in Si-nc. We consider B and P substitutional impurities for Si-nc with a diameter up to 2.2 nm. Formation energies (FEs), electronic, optical and structural properties have been determined as a function of the cluster dimension. For both B-doped and P-doped Si-nc the FE increases on decreasing the dimension, showing that the substitutional doping gets progressively more difficult for the smaller nanocrystals. Moreover, subsurface impurity positions result to be the most stable ones. The codoping reduces the FE strongly favoring this process with respect to the simple n-doping or p-doping. Such an effect can be attributed to charge compensation between the donor and the acceptor atoms. Moreover, smaller structural deformations, with respect to n-doped and p-doped cases, localized only around the impurity sites are observed. The band gap and the optical threshold are largely reduced with respect to the undoped Si-nc showing the possibility of an impurity-based engineering of the Si-nc PL properties
Electronic structure and magnetism of titanium substituted Cd3P2: An ab-initio study
Jaiganesh, G.; Jaya, S. Mathi
2018-05-01
Using the ab-initio computations that are based on the density functional theory, we have investigated the magnetism and electronic properties of one and two Ti atom substituted Cd3P2 compound. The magnetic stability of the substituted compounds was obtained by analyzing the minimum total energies in nonmagnetic, ferromagnetic and antiferromagnetic phases. Our results indicated the formation of magnetic order in one and two Ti atom substituted Cd3P2 as well as metallic characteristics in these systems. A significant value of the magnetic moment of Ti atom is observed from our calculations. We further find that the neighboring Cd and P atoms too acquire a small magnetic moment.
International Nuclear Information System (INIS)
Mugnaioli, E.; Gorelik, T.; Kolb, U.
2009-01-01
Using a combination of our recently developed automated diffraction tomography (ADT) module with precession electron technique (PED), quasi-kinematical 3D diffraction data sets of an inorganic salt (BaSO 4 ) were collected. The lattice cell parameters and their orientation within the data sets were found automatically. The extracted intensities were used for 'ab initio' structure analysis by direct methods. The data set covered almost the complete set of possible symmetrically equivalent reflections for an orthorhombic structure. The structure solution in one step delivered all heavy (Ba, S) as well as light atoms (O). Results of the structure solution using direct methods, charge flipping and maximum entropy algorithms as well as structure refinement for three different 3D electron diffraction data sets were presented.
Roy, Soumendra K.; Jian, Tian; Lopez, Gary V.; Li, Wei-Li; Su, Jing; Bross, David H.; Peterson, Kirk A.; Wang, Lai-Sheng; Li, Jun
2016-02-01
The observation of the gaseous UFO- anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO- is linear with an O-U-F structure and a 3H4 spectral term derived from a U 7sσ25fφ15fδ1 electron configuration, whereas the ground state of neutral UFO has a 4H7/2 spectral term with a U 7sσ15fφ15fδ1 electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.
Bano, Amreen; Gaur, N. K.
2018-05-01
Ab-initio calculations are carried out to study the electronic and chemical bonding properties of Intermetallic full Heusler compound Pd2HfIn which crystallizes in F-43m structure. All calculations are performed by using density functional theory (DFT) based code Quantum Espresso. Generalized gradient approximations (GGA) of Perdew- Burke- Ernzerhof (PBE) have been adopted for exchange-correlation potential. Calculated electronic band structure reveals the metallic character of the compound. From partial density of states (PDoS), we found the presence of relatively high intensity electronic states of 4d-Pd atom at Fermi level. We have found a pseudo-gap just abouve the Fermi level and N(E) at Fermi level is observed to be 0.8 states/eV, these finding indicates the existence of superconducting character in Pd2HfIn.
International Nuclear Information System (INIS)
Souto, J; Alemany, M M G; Gallego, L J; González, L E; González, D J
2013-01-01
We report an ab initio molecular dynamics study of the static, dynamic and electronic properties of the liquid Bi x Li 1−x alloy, which is a complex binary system with a marked tendency to heterocoordination. The calculated total static structure factors are in good agreement with the available experimental data. The partial dynamic structure factors exhibit side peaks indicative of propagating density fluctuations, and for some concentrations we have found a density fluctuation mode with phase velocity greater than the hydrodynamic sound velocity. We have also evaluated other dynamical properties such as the diffusion coefficients, the shear viscosity and the adiabatic sound velocity. The electronic density of states show that the liquid Bi x Li 1−x alloy has a metallic character, although with strong deviations from the free-electron parabolic curve. The results reported improve the understanding of binary liquid alloys with both fast and slow propagating collective modes. (paper)
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Trevisanutto, Paolo E. [Graphene Research Centre and CA2DM, National University of Singapore, Singapore 117542, Singapore and Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603 (Singapore); Vignale, Giovanni, E-mail: vignaleg@missouri.edu [Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211 (United States)
2016-05-28
Ab initio electronic structure calculations of two-dimensional layered structures are typically performed using codes that were developed for three-dimensional structures, which are periodic in all three directions. The introduction of a periodicity in the third direction (perpendicular to the layer) is completely artificial and may lead in some cases to spurious results and to difficulties in treating the action of external fields. In this paper we develop a new approach, which is “native” to quasi-2D materials, making use of basis function that are periodic in the plane, but atomic-like in the perpendicular direction. We show how some of the basic tools of ab initio electronic structure theory — density functional theory, GW approximation and Bethe-Salpeter equation — are implemented in the new basis. We argue that the new approach will be preferable to the conventional one in treating the peculiarities of layered materials, including the long range of the unscreened Coulomb interaction in insulators, and the effects of strain, corrugations, and external fields.
Devi, Assa Aravindh Sasikala
2014-05-01
Investigations on freestanding binary and ternary clusters of Fe (x) Co (y) Ir (z) (x + y + z = 5, 6) are carried out using ab initio density functional theory techniques. The geometry, chemical order, binding energy, magnetic moment and electronic structure of the clusters are analyzed for the entire range of composition. Composition dependent structural transition is observed in the five atom clusters, while octahedral geometry prevailed in clusters with six atoms. Both the clusters show increment in binding energy with the increase in number of heterogeneous bonds. Analysis based on the chemical order parameter indicates that clusters favor mixing rather than segregation. The clusters exhibit ferromagnetic ordering and the inter-dependence of optimal cluster geometry to the magnetic moments and electronic structure is observed.
Devi, Assa Aravindh Sasikala
2014-01-01
Investigations on freestanding binary and ternary clusters of Fe (x) Co (y) Ir (z) (x + y + z = 5, 6) are carried out using ab initio density functional theory techniques. The geometry, chemical order, binding energy, magnetic moment and electronic
Ab initio electronic band structure calculation of InP in the wurtzite phase
Dacal, Luis C. O.; Cantarero, Andrés
2011-05-01
We present ab initio calculations of the InP band structure in the wurtzite phase and compare it with that of the zincblende phase. In both calculations, we use the full potential linearized augmented plane wave method as implemented in the WIEN2k code and the modified Becke-Johnson exchange potential, which provides an improved value of the bandgap. The structural optimization of the wurtizte InP gives a=0.4150 nm, c=0.6912 nm, and an internal parameter u=0.371, showing the existence of a spontaneous polarization along the growth axis. As compared to the ideal wurtzite structure (that with the lattice parameter derived from the zincblende structure calculations), the actual wurtzite structure is compressed (-1.3%) in plane and expanded (0.7%) along the c-direction. The value of the calculated band gaps agrees well with recent optical experiments. The calculations are also consistent with the optical transitions found using polarized light.
Kim, Jeongnim; Baczewski, Andrew D.; Beaudet, Todd D.; Benali, Anouar; Chandler Bennett, M.; Berrill, Mark A.; Blunt, Nick S.; Josué Landinez Borda, Edgar; Casula, Michele; Ceperley, David M.; Chiesa, Simone; Clark, Bryan K.; Clay, Raymond C., III; Delaney, Kris T.; Dewing, Mark; Esler, Kenneth P.; Hao, Hongxia; Heinonen, Olle; Kent, Paul R. C.; Krogel, Jaron T.; Kylänpää, Ilkka; Li, Ying Wai; Lopez, M. Graham; Luo, Ye; Malone, Fionn D.; Martin, Richard M.; Mathuriya, Amrita; McMinis, Jeremy; Melton, Cody A.; Mitas, Lubos; Morales, Miguel A.; Neuscamman, Eric; Parker, William D.; Pineda Flores, Sergio D.; Romero, Nichols A.; Rubenstein, Brenda M.; Shea, Jacqueline A. R.; Shin, Hyeondeok; Shulenburger, Luke; Tillack, Andreas F.; Townsend, Joshua P.; Tubman, Norm M.; Van Der Goetz, Brett; Vincent, Jordan E.; ChangMo Yang, D.; Yang, Yubo; Zhang, Shuai; Zhao, Luning
2018-05-01
QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater–Jastrow type trial wavefunctions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary-field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit and graphical processing unit systems. We detail the program’s capabilities, outline its structure, and give examples of its use in current research calculations. The package is available at http://qmcpack.org.
International Nuclear Information System (INIS)
Termentzidis, K; Pokropivny, A; Xiong, S-Y; Chumakov, Y; Volz, S; Woda, M; Cortona, P
2012-01-01
We use molecular dynamics and ab-initio methods to predict the thermal and electronic properties of new materials with high figures of merit. The simulated systems are bulk bismuth tellurides with antisite and vacancy defects. Optimizations of the materials under investigation are performed by the SIESTA code for subsequent calculations of force constants, electronic properties, and Seebeck coefficients. The prediction of the thermal conductivity is made by Non-Equilibrium Molecular Dynamics (NEMD) using the LAMMPS code. The thermal conductivity of bulk bismuth telluride with different stoichiometry and with a number of substitution defects is calculated. We have found that the thermal conductivity can be decreased by 60% by introducing vacancy defects. The calculated thermal conductivities for the different structures are compared with the available experimental and theoretical results.
Accuracy and Transferability of Ab Initio Electronic Band Structure Calculations for Doped BiFeO3
Gebhardt, Julian; Rappe, Andrew M.
2017-11-01
BiFeO3 is a multiferroic material and, therefore, highly interesting with respect to future oxide electronics. In order to realize such devices, pn junctions need to be fabricated, which are currently impeded by the lack of successful p-type doping in this material. In order to guide the numerous research efforts in this field, we recently finished a comprehensive computational study, investigating the influence of many dopants onto the electronic structure of BiFeO3. In order to allow for this large scale ab initio study, the computational setup had to be accurate and efficient. Here we discuss the details of this assessment, showing that standard density-functional theory (DFT) yields good structural properties. The obtained electronic structure, however, suffers from well-known shortcomings. By comparing the conventional DFT results for alkali and alkaline-earth metal doping with more accurate hybrid-DFT calculations, we show that, in this case, the problems of standard DFT go beyond a simple systematic error. Conventional DFT shows bad transferability and the more reliable hybrid-DFT has to be chosen for a qualitatively correct prediction of doping induced changes in the electronic structure of BiFeO3.
Ab initio studies of the electronic structure of the quaternary system LiBC4N4
International Nuclear Information System (INIS)
Matar, S.F.; Betranhandy, E.; Nakhl, M.
2007-01-01
Starting from experimental data on the synthesis of solid LiBC 4 N 4 , an ab initio study has been carried out within the DFT-LDA framework of its structure and completed by accounting for other potential cubic arrangements. The consideration of stabilization energies confirms the experimental phase as the most stable one but predicts some other potential arrangements. The system is found very compressible with a bulk modulus close to that of gypsum (B 0 = 35 GPa). The electronic structure characteristics are provided allowing to confirm an ionic behavior involving complex anionic species (Li + [B(China) 4 ] - ). The control of the crystal cell size by a stoichiometry modification, such as by a CN group substitution is also studied. The proposition of LiBX 4 and LiBS 4 N 4 stoichiometries leads to predict new materials
Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun
2016-02-28
The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.
Krysiak, Yaşar; Barton, Bastian; Marler, Bernd; Neder, Reinhard B; Kolb, Ute
2018-03-01
Nanoscaled porous materials such as zeolites have attracted substantial attention in industry due to their catalytic activity, and their performance in sorption and separation processes. In order to understand the properties of such materials, current research focuses increasingly on the determination of structural features beyond the averaged crystal structure. Small particle sizes, various types of disorder and intergrown structures render the description of structures at atomic level by standard crystallographic methods difficult. This paper reports the characterization of a strongly disordered zeolite structure, using a combination of electron exit-wave reconstruction, automated diffraction tomography (ADT), crystal disorder modelling and electron diffraction simulations. Zeolite beta was chosen for a proof-of-principle study of the techniques, because it consists of two different intergrown polymorphs that are built from identical layer types but with different stacking sequences. Imaging of the projected inner Coulomb potential of zeolite beta crystals shows the intergrowth of the polymorphs BEA and BEB. The structures of BEA as well as BEB could be extracted from one single ADT data set using direct methods. A ratio for BEA/BEB = 48:52 was determined by comparison of the reconstructed reciprocal space based on ADT data with simulated electron diffraction data for virtual nanocrystals, built with different ratios of BEA/BEB. In this way, it is demonstrated that this smart interplay of the above-mentioned techniques allows the elaboration of the real structures of functional materials in detail - even if they possess a severely disordered structure.
Czech Academy of Sciences Publication Activity Database
Vřešťál, J.; Kroupa, Aleš; Šob, Mojmír
2006-01-01
Roč. 38, č. 11 (2006), s. 298-302 ISSN 0927-0256 R&D Projects: GA ČR(CZ) GA106/03/1354; GA AV ČR(CZ) IBS2041105 Institutional research plan: CEZ:AV0Z20410507 Keywords : electronic structure * Phase diagrams * Steel Subject RIV: BJ - Thermodynamics Impact factor: 1.104, year: 2006
Ab initio investigations of the electronic structure and chemical bonding of Li2ZrN2
International Nuclear Information System (INIS)
Matar, S.F.; Pöttgen, R.; Al Alam, A.F.; Ouaini, N.
2012-01-01
The electronic structure of the ternary nitride Li 2 ZrN 2 is examined from ab initio with DFT computations for an assessment of the properties of chemical bonding. The compound is found insulating with 1.8 eV band gap; it becomes metallic and less ionic upon removal of one equivalent of Li. The chemical interaction is found mainly between Zr and N on one hand and Li and N on the other hand. While all pair interactions are bonding, antibonding N–N interactions are found dominant at the top of the valence band of Li 2 ZrN 2 and they become less intense upon removal of Li. From energy differences the partial delithiation leading to Li 2−x ZrN 2 (x=∼1) is favored. - Graphical abstract: Trigonal structure of Li 2 ZrN 2 showing the Zr–N–Li layers along the c-axis. Highlights: ► Li 2 ZrN 2 calculated insulating with a 1.8 eV gap in agreement with its light green color. ► Lithium de-intercalation is energetically favored for one out of two Li equivalents. ► Li plays little role in the change of the structure, ensured by Zr and N binding. ► Similar changes in the electronic structure as for various intercalated phases of ZrN.
Energy Technology Data Exchange (ETDEWEB)
Car, R.; Parrinello, M.
1988-01-18
An amorphous silicon structure is obtained with a computer simulation based on a new molecular-dynamics technique in which the interatomic potential is derived from a parameter-free quantum mechanical method. Our results for the atomic structure, the phonon spectrum, and the electronic properties are in excellent agreement with experiment. In addition we study details of the microscopic dynamics which are not directly accessible to experiment. We find in particular that structural defects are associated with weak bonds. These may give rise to low-frequency vibrational modes.
Kim, Jaehyun; Kang, Jiyoung; Nishigami, Hiroshi; Kino, Hiori; Tateno, Masaru
2018-03-01
Hydrogenases catalyze both the dissociation and production of dihydrogen (H2). Most hydrogenases are inactivated rapidly and reactivated slowly (in vitro), in the presence of dioxygen (O2) and H2, respectively. However, membrane-bound [NiFe] hydrogenases (MBHs) sustain their activity even together with O2, which is termed "O2 tolerance". In previous experimental analyses, an MBH was shown to include a hydroxyl ion (OH-) bound to an Fe of the super-oxidized [4Fe-3S]5+ cluster in the proximity of the [NiFe] catalytic cluster. In this study, the functional role of the OH- in the O2 tolerance was investigated by ab initio electronic structure calculation of the [4Fe-3S] proximal cluster. The analysis revealed that the OH- significantly altered the electronic structure, thereby inducing the delocalization of the lowest unoccupied molecular orbital (LUMO) toward the [NiFe] catalytic cluster, which may intermediate the electron transfer between the catalytic and proximal clusters. This can promote the O2-tolerant catalytic cycle in the hydrogenase reaction.
Czech Academy of Sciences Publication Activity Database
Hemzalová, P.; Friák, Martin; Šob, Mojmír; Ma, D.; Udyansky, A.; Raabe, D.; Neugebauer, J.
2013-01-01
Roč. 88, č. 17 (2013), Art. no. 174103 ISSN 1098-0121 R&D Projects: GA ČR(CZ) GAP108/12/0311; GA ČR GD106/09/H035; GA AV ČR IAA100100920 Institutional support: RVO:68081723 Keywords : nitrides * ab initio * thermodynamics * elasticity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.664, year: 2013
Structural and electronic properties of AlX (X = P, As, Sb) nanowires: Ab initio study
International Nuclear Information System (INIS)
Srivastava, Anurag; Tyagi, Neha
2012-01-01
Present paper discusses the structural stability and electronic properties of AlX (X = P, As and Sb) nanowires in its linear, zigzag, ladder, square and hexagonal type atomic configurations. The structural optimization has been performed in self consistence manner by using generalized gradient approximation with revised Perdew, Burke and Ernzerhof type parameterization. The study observes that in all the three nanowires, the square shaped atomic configuration is the most stable one. The calculated electronic band structures and density of states profile confirms the semiconducting behaviour of linear and zigzag shaped nanowires of AlP, whereas for AlAs and AlSb nanowires are metallic. The ground state properties have also been analysed in terms of bond length, bulk modulus and pressure derivative for all the nanowires along with their bulk counterpart. The lower bulk modulus of all the linear shaped geometries of AlX nanowires in comparison to its bulk counterpart indicates softening of the material at reduced dimension. -- Graphical abstract: Figure-Electronic band structure of zigzag shaped AlP nanowire. The present electronic band structures of zigzag and linear shaped AlP nanowires are showing a clear band gap at Γ point, however others (AlAs and AlSb) in zigzag as well as in linear shape show metallic behaviour. Highlights: ► Stability analysis of five geometries of AlX (X = P, As and Sb) nanowires studied. ► Square shaped geometry of AlX nanowires is most stable. ► Linear and zigzag shaped AlP nanowires are semiconducting. ► Bulk moduli of all the linear nanowires are lower than their bulk counterpart. ► Lower bulk moduli defends the softening of material.
Energy Technology Data Exchange (ETDEWEB)
Almeida, Wagner B. de [Minas Gerais Univ., Belo Horizonte, MG (Brazil). Dept. de Quimica
2000-10-01
The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase an initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions. (author)
Ab initio investigation of the structural and electronic properties of amorphous HgTe
International Nuclear Information System (INIS)
Zhao, Huxian; Chen, Xiaoshuang; Shu, Haibo; Lu, Wei; Lu, Jianping
2014-01-01
We present the structure and electronic properties of amorphous mercury telluride obtained from first-principle calculations. The initial configuration of amorphous mercury telluride is created by computation alchemy. According to different exchange–correlation functions in our calculations, we establish two 256-atom models. The topology of both models is analyzed in terms of radial and bond angle distributions. It is found that both the Te and the Hg atoms tend to be fourfold, but with a wrong bond rate of about 10%. The fraction of threefold and fivefold atoms also shows that there are a significant number of dangling and floating bonds in our models. The electronic properties are also obtained. It is indicated that there is a bandgap in amorphous HgTe, in contrast to the zero bandgap for crystalline HgTe. The structures of the band tail and defect states are also discussed. (paper)
Ab initio investigation of the structural and electronic properties of amorphous HgTe.
Zhao, Huxian; Chen, Xiaoshuang; Lu, Jianping; Shu, Haibo; Lu, Wei
2014-01-29
We present the structure and electronic properties of amorphous mercury telluride obtained from first-principle calculations. The initial configuration of amorphous mercury telluride is created by computation alchemy. According to different exchange–correlation functions in our calculations, we establish two 256-atom models. The topology of both models is analyzed in terms of radial and bond angle distributions. It is found that both the Te and the Hg atoms tend to be fourfold, but with a wrong bond rate of about 10%. The fraction of threefold and fivefold atoms also shows that there are a significant number of dangling and floating bonds in our models. The electronic properties are also obtained. It is indicated that there is a bandgap in amorphous HgTe, in contrast to the zero bandgap for crystalline HgTe. The structures of the band tail and defect states are also discussed.
Directory of Open Access Journals (Sweden)
Devi Prasadh P.S.
2017-06-01
Full Text Available Based on Density Functional Theory, we have applied Full Potential Augmented Plane Wave plus local orbital method (FAPW+loto study the electronic, structural, optical, thermal and mechanical properties of some semiconducting materials. In this paper we discuss the Zinc blende, CdX (X = S, Se and Te compounds with the full-potential linear-augmented plane wave (FP-LAPW method within the framework of the density functional theory (DFT for electronic, structural, thermal and mechanical properties using the WIEN2k code. For the purpose of exchange-correlation energy (Exc determination in Kohn–Sham calculation, the standard local density approximation (LDA formalism is utilized. Murnaghan’s equation of state (EOS is used for volume optimization by minimizing the total energy with respect to the unit cell volume. The calculated lattice parameters and thermal parameters are in good agreement with other theoretical calculations as well as available experimental data.
Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.
1997-01-01
The method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to simulate laser heating of crystalline silicon. We found that a high concentration of excited electrons dramatically weakens the covalent bonding. As a result the system undergoes a melting
Energy Technology Data Exchange (ETDEWEB)
Mokhtari, A.; Akbarzadeh, H
2003-09-01
The electronic and structural properties of beryllium nitride (alpha and beta), magnesium- and calcium-nitrides were investigated using first principle full potential-linearized augmented plane wave method within density functional theory. We used Perdew and Wang-generalized gradient approximation, which is based on exchange correlation energy optimization, to calculate the total energy and the Engel-Vosko's GGA formalism, which optimize the corresponding potential, for band structure calculations. We also optimized internal parameters by relaxing the atomic positions in the force directions. Our results including lattice parameter, bulk modulus and it's pressure derivative, cohesive energy, band structure and density of states are compared with the experimental and other theoretical (Hartree-Fock approximation with a posteriori density functional correction) data.
International Nuclear Information System (INIS)
Mokhtari, A.; Akbarzadeh, H.
2003-01-01
The electronic and structural properties of beryllium nitride (alpha and beta), magnesium- and calcium-nitrides were investigated using first principle full potential-linearized augmented plane wave method within density functional theory. We used Perdew and Wang-generalized gradient approximation, which is based on exchange correlation energy optimization, to calculate the total energy and the Engel-Vosko's GGA formalism, which optimize the corresponding potential, for band structure calculations. We also optimized internal parameters by relaxing the atomic positions in the force directions. Our results including lattice parameter, bulk modulus and it's pressure derivative, cohesive energy, band structure and density of states are compared with the experimental and other theoretical (Hartree-Fock approximation with a posteriori density functional correction) data
International Nuclear Information System (INIS)
Minár, J.; Braun, J.; Ebert, H.
2013-01-01
Highlights: ► We compare spin-resolved ARPES data of ferromagnetic 3d transition metals to many-body LSDA + DMFT based spectroscopic calculations. ► We document LSDA + DMFT provides a detailed and reliable interpretation of the data. ► We demonstrate that local correlations are dominant in Ni, whereas non-local correlations are important in Fe and Co. ► We reproduce the 6 eV satellite structure in ferromagnetic Ni LDSDA + DMFT in combination with the one-step model of photoemission provides a more or less complete description of the electronic structure of Fe, Co and Ni. -- Abstract: Various technical developments enlarged the potential of angle-resolved photoemission spectroscopy (ARPES) tremendously during the last two decades. In particular improved momentum and energy resolution in combination with spin-resolution as well as the use of photon energies from few eV up to several keV makes ARPES a rather unique tool to investigate the electronic properties of solids and surfaces. Obviously, this rises the need for a corresponding theoretical formalism that allows to accompany experimental ARPES studies in an adequate way. As will be demonstrated by several examples this goal could be achieved by various recent developments on the basis of density functional theory (DFT) in combination with dynamical mean field theory (DMFT) and with the one-step model of photoemission (1SM). A concrete realization of electronic structure calculations in the framework of multiple scattering theory further more provides direct access to the spectral function of the initial states via the one-electron Green function. Based on this bare spectral function matrix-element and final-state effects as well as surface related features may be calculated in addition using the one-step formalism that offers the possibility to analyse corresponding angle-resolved photoemission experiments in a quantitative sense. The impact of chemical disorder can be handled by means of the coherent
International Nuclear Information System (INIS)
Dacal, Luis C O; Cantarero, A
2014-01-01
Most III–V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the Γ–point of the Brillouin zone (E 0 gap) has been recently measured, E 0 =0.46 eV at low temperature. The electronic gap at the A–point of the Brillouin zone (equivalent to the L–point in the zinc-blende structure, E 1 ) has also been obtained recently based on a resonant Raman scattering experiment. In this work, we calculate the band structure of InAs in the zinc-blende and wurtzite phases, using the full potential linearized augmented plane wave method, including spin-orbit interaction. The electronic band gap has been improved through the modified Becke–Johnson exchange-correlation potential. Both the E 0 and E 1 gaps agree very well with the experiment. From the calculations, a crystal field splitting of 0.122 eV and a spin-orbit splitting of 0.312 eV (the experimental value in zinc-blende InAs is 0.4 eV) has been obtained. Finally, we calculate the dielectric function of InAs in both the zinc-blende and wurtzite phases and a comparative discussion is given. (paper)
Dacal, Luis C. O.; Cantarero, A.
2014-03-01
Most III-V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the \\Gamma -point of the Brillouin zone ({{E}_{0}} gap) has been recently measured, {{E}_{0}}=0.46 eV at low temperature. The electronic gap at the A-point of the Brillouin zone (equivalent to the L-point in the zinc-blende structure, {{E}_{1}}) has also been obtained recently based on a resonant Raman scattering experiment. In this work, we calculate the band structure of InAs in the zinc-blende and wurtzite phases, using the full potential linearized augmented plane wave method, including spin-orbit interaction. The electronic band gap has been improved through the modified Becke-Johnson exchange-correlation potential. Both the {{E}_{0}} and {{E}_{1}} gaps agree very well with the experiment. From the calculations, a crystal field splitting of 0.122 eV and a spin-orbit splitting of 0.312 eV (the experimental value in zinc-blende InAs is 0.4 eV) has been obtained. Finally, we calculate the dielectric function of InAs in both the zinc-blende and wurtzite phases and a comparative discussion is given.
Ab initio theory of the electronic structure of nf-ions in solids and liquids
International Nuclear Information System (INIS)
Kulagin, N.
1998-01-01
Full text: In the books and papers we developed the self-consistent field theory of nl- ions in Me+n:[L]k- clusters, where k is number of ligands - L, by ion-ligands distance - R. The results which were obtained for all RE and AC ions for Me+n:[L]k, where L - F - , O -2 and so on ligands, are closely corresponded to experimental data. The expression for energy of the cluster may be write as: E = E 0 + kE 1 + k'(E z + E c + E e + E ex ), (Eq.1), where E 0 and E 1 are the energies of the free nl-ion and surrounding one; E z , E c and E e are the energy of electrons interaction with 'strange' nucleus, Coulomb electron-electron interaction and exchange one. E ex is the energy of the interaction of electrons and nucleus with external field. The equations for the radial one-electron wave functions of the ions in the cluster were obtained by minimizing the Eq. 1 for the radial orbitals of the central ion and ligand one. We have received the general system of equations of the self-consistent field for cluster in liquids and solid states. The results of calculations of the energy structure of clusters and values of the standard radial integrals (spectroscopy parameters) for Ac-ions in 1-2-3 superconductors and RE-ions in garnet crystals by different values of R are qualitatively and quantitatively correct. We've got the best results for pressure dependence of Nd ions spectra, change of optical and X-Ray spectra after irradiation of garnets. We explained the nature of anomalous in SrTiO 3 and separate lasers crystals by used of results of the calculations. In the framework of our approach we obtained the best accuracy for the energy of X- Ray lines for all nf- ions in solids and liquids
International Nuclear Information System (INIS)
Yadav, P. S.; Pandey, D. K.; Agrawal, S.; Agrawal, B. K.
2010-01-01
An ab initio study of the stability, structural, electronic. and optical properties has been performed for 46 zinc sulfide nanoclusters Zn x S y (x + y = n = 2 to 5). Five out of them are seen to be unstable as their vibrational frequencies are found to be imaginary. A B3LYP-DFT/6-311G(3df) method is employed to optimize the geometries and a TDDFT method is used for the study of the optical properties. The binding energies (BE), HOMO-LUMO gaps and the bond lengths have been obtained for all the clusters. For the ZnS 2 , ZnS 3 , and ZnS 4 nanoclusters, our stable structures are seen to be different from those obtained earlier by using the effective core potentials. We have also considered the zero point energy (ZPE) corrections ignored by the earlier workers. For a fixed value of n, we designate the most stable structure the one, which has maximum final binding energy per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), charges on the atoms, dipole moments, optical properties, vibrational frequencies, infrared intensities, relative infrared intensities, and Raman scattering activities have been investigated for the most stable structures. The nanoclusters containing large number of S atoms for each n is found to be most stable. The HOMO-LUMO gap decreases from n = 2-3 and then increases above n = 3. The IP and EA both fluctuate with the cluster size n. The optical absorption is quite weak in visible region but strong in the ultraviolet region in most of the nanoclusters except a few. The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every nanocluster and may be used to characterize a specific nanocluster. The growth of most stable nanoclusters may be possible in the experiments.
Energy Technology Data Exchange (ETDEWEB)
Jalilian, Jaafar, E-mail: JaafarJalilian@gmail.com [Young Researchers and Elite Club, Kermanshah Br anch, Islamic Azad University, P.O. Box: 6718997551, Kermanshah (Iran, Islamic Republic of); Kanjouri, Faramarz, E-mail: kanjouri@khu.ac.ir [Physics Department, Faculty of Science, Kharazmi University, University Square, P.O. Box: 3197937551, Karaj (Iran, Islamic Republic of)
2016-11-15
Using spin-polarized density functional theory calculations, we demonstrated that carbon doped boron nitride nanowire (C-doped BNNW) has diverse electronic and magnetic properties depending on position of carbon atoms and their percentages. Our results show that only when one carbon atom is situated on the edge of the nanowire, C-doped BNNW is transformed into half-metal. The calculated electronic structure of the C-doped BNNW suggests that doping carbon can induce localized edge states around the Fermi level, and the interaction among localized edge states leads to semiconductor to half-metal transition. Overall, the bond reconstruction causes of appearance of different electronic behavior such as semiconducting, half-metallicity, nonmagnetic metallic, and ferromagnetic metallic characters. The formation energy of the system shows that when a C atom is doped on surface boron site, system is more stable than the other positions of carbon impurity. Our calculations show that C-doped BNNW may offer unique opportunities for developing nanoscale spintronic materials.
International Nuclear Information System (INIS)
Bernholc, J.
1998-01-01
The field of computational materials physics has grown very quickly in the past decade, and it is now possible to simulate properties of complex materials completely from first principles. The presentation has mostly focused on first-principles dynamic simulations. Such simulations have been pioneered by Car and Parrinello, who introduced a method for performing realistic simulations within the context of density functional theory. The Car-Parrinello method and related plane wave approaches are reviewed in depth. The Car-Parrinello method was reviewed and illustrated with several applications: the dynamics of the C 60 solid, diffusion across Si steps, and computing free energy differences. Alternative ab initio simulation schemes, which use preconditioned conjugate gradient techniques for energy minimization and dynamics were also discussed
Energy Technology Data Exchange (ETDEWEB)
Genderen, E. van; Clabbers, M. T. B. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, CH-4058 Basel (Switzerland); Das, P. P. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Stewart, A. [Department of Physics and Energy, Materials and Surface Science Institute (MSSI), University of Limerick, Limerick (Ireland); Nederlof, I. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Amsterdam Scientific Instruments, Postbus 41882, 1009 DB Amsterdam (Netherlands); Barentsen, K. C. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Portillo, Q. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Centres Científics i Tecnològics de la Universitat de Barcelona, University of Barcelona, Carrer de Lluís Solé i Sabaris, 1-3, Barcelona (Spain); Pannu, N. S. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Nicolopoulos, S. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Gruene, T., E-mail: tim.gruene@psi.ch [Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen (Switzerland); Abrahams, J. P., E-mail: tim.gruene@psi.ch [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, CH-4058 Basel (Switzerland); Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen (Switzerland)
2016-02-05
A specialized quantum area detector for electron diffraction studies makes it possible to solve the structure of small organic compound nanocrystals in non-cryo conditions by direct methods. Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼0.013 e{sup −} Å{sup −2} s{sup −1}) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014)
Ab initio electronic band structure study of III-VI layered semiconductors
Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés
2013-08-01
We present a total energy study of the electronic properties of the rhombohedral γ-InSe, hexagonal ɛ-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.
Ab initio investigations of the electronic structure and chemical bonding of Li{sub 2}ZrN{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Matar, S.F., E-mail: matar@icmcb-bordeaux.cnrs.fr [CNRS, Universite de Bordeaux, ICMCB, 87 Avenue du Docteur Albert Schweitzer, 33600 Pessac (France); Poettgen, R., E-mail: pottgen@uni-muenster.de [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Al Alam, A.F., E-mail: adelalalam@usek.edu.lb [Universite Saint Esprit de Kaslik (USEK), Faculte des Sciences, URA GREVE (CNRS/USEK/UL), Jounieh (Lebanon); Ouaini, N., E-mail: naimouaini@usek.edu.lb [Universite Saint Esprit de Kaslik (USEK), Faculte des Sciences, URA GREVE (CNRS/USEK/UL), Jounieh (Lebanon)
2012-06-15
The electronic structure of the ternary nitride Li{sub 2}ZrN{sub 2} is examined from ab initio with DFT computations for an assessment of the properties of chemical bonding. The compound is found insulating with 1.8 eV band gap; it becomes metallic and less ionic upon removal of one equivalent of Li. The chemical interaction is found mainly between Zr and N on one hand and Li and N on the other hand. While all pair interactions are bonding, antibonding N-N interactions are found dominant at the top of the valence band of Li{sub 2}ZrN{sub 2} and they become less intense upon removal of Li. From energy differences the partial delithiation leading to Li{sub 2-x}ZrN{sub 2} (x={approx}1) is favored. - Graphical abstract: Trigonal structure of Li{sub 2}ZrN{sub 2} showing the Zr-N-Li layers along the c-axis. Highlights: Black-Right-Pointing-Pointer Li{sub 2}ZrN{sub 2} calculated insulating with a 1.8 eV gap in agreement with its light green color. Black-Right-Pointing-Pointer Lithium de-intercalation is energetically favored for one out of two Li equivalents. Black-Right-Pointing-Pointer Li plays little role in the change of the structure, ensured by Zr and N binding. Black-Right-Pointing-Pointer Similar changes in the electronic structure as for various intercalated phases of ZrN.
International Nuclear Information System (INIS)
Bezi Javan, Masoud
2015-01-01
Highlights: • Electronic and magnetic properties of small Zr n Pd m (n + m ⩽ 5) have been investigated. • Binding energies of the Zr n clusters are significantly higher than Pd n clusters. • Binding energy of the Pd n clusters increase with substituting one or more Zr atom. • HOMO–LUMO gap of the Zr n Pd m clusters increase in comparison with pure states. - Abstract: Structural, electronic and magnetic properties of small bimetallic zirconium–palladium clusters, Zr n Pd m (n + m ⩽ 5), have been investigated using density functional theory with considering generalized gradient approximation and PBE functional. We have determined the ground state conformations of the bimetallic zirconium–palladium clusters by substitution of Zr and Pd atoms in the optimized lowest energy structures of pure zirconium and palladium clusters. Results reveal that binding energies of the pure Zr n clusters are significantly higher than Pd n clusters with the same number of atoms. Also it is found that binding energy of the Zr n and Pd n clusters increase with growth of the number of consisting atoms in the clusters. Results indicate that, for both Zr n and Pd n clusters the binding energy of planar forms is lower than three-dimensional structures. We have also found that the binding energy of the Pd n clusters increase with substituting one or more Zr atoms in these clusters. We have also studied the HOMO–LUMO energy gap and magnetic moment of the pure and combined Zr and Pd clusters. The energy gap analysis of the pure and combined Pd and Zr clusters show that in generally the HOMO–LUMO gap of the bimetallic Zr n Pd m clusters increase in comparison with their corresponding pure clusters with the same number of atoms. According to the spin polarization DFT calculations all of the Zr n Pd m (n + m ⩽ 5) have net magnetic moments as instance the Zr 2 , Pd 2 and ZrPd clusters show a total magnetic moment value of 2 μ B . Some more discussions around charge population
Ab-initio study of structural and electronic properties of WS2/h-BN van der Waals heterostructure
Ghasemi majd, Zahra; Amiri, Peiman; Taghizadeh, Seyed Fardin
2018-06-01
First-principle calculations with different exchange-correlation functionals, including LDA, GGA, semi-empirical and ab-initio van der Waals in the forms of vdW-DF2B86R and vdW-DF2 were performed to evaluate the performance of different functionals in describing the bonding mechanism, adsorption energy and interlayer distance of WS2 monolayer on and between h-BN layers. The finding was that the vdW-DF2B86R seems to be the approach best lending itself to this purpose. In order to include the van der Waals (vdW) interactions in our calculations, we used the DFT-D2 and vdW methods, which gave rise to a physical adsorption with no net charge transfer between the WS2 layer and the corresponding substrates. In addition, we investigated the electronic and structural properties of WS2 and h-BN heterolayers, using vdW-DF2B86R functional. Based on density functional theory calculations, WS2 on and between h-BN layers showed a direct band gap at the K-point, which was experimentally observed.
International Nuclear Information System (INIS)
Olsson, Paer
2004-04-01
The efficiency of fast neutron reactors, such as for fusion, breeding and transmutation, depend strongly on the neutron radiation resistance of the materials used in the reactors. The binary Fe-Cr alloy, which has many attractive properties in this regard, is the base for the best steels of today which are, however, still not up to the required standards. Therefore, substantial effort has been devoted to finding new materials that can cope with the demands better. Experimental studies must be complemented with extensive theoretical modelling in order to understand the effects that different alloying elements has on the resistance properties of materials. To this end, the first steps of multi-scale modelling has been taken, starting out with ab initio calculations of the electronic structure of the complete concentration range range of the disordered binary Fe-C alloy. The mixing enthalpy of Fe-Cr has been quantitatively predicted and has, together with data from literature, been used in order to fit two sets of interatomic potentials for the purpose of simulating defect evolution with molecular dynamics and kinetic Monte-Carlo codes. These dedicated Fe-Cr alloy potentials are new and represent important additions to the pure element potentials that can be found in literature
Energy Technology Data Exchange (ETDEWEB)
Olsson, Paer
2004-04-01
The efficiency of fast neutron reactors, such as for fusion, breeding and transmutation, depend strongly on the neutron radiation resistance of the materials used in the reactors. The binary Fe-Cr alloy, which has many attractive properties in this regard, is the base for the best steels of today which are, however, still not up to the required standards. Therefore, substantial effort has been devoted to finding new materials that can cope with the demands better. Experimental studies must be complemented with extensive theoretical modelling in order to understand the effects that different alloying elements has on the resistance properties of materials. To this end, the first steps of multi-scale modelling has been taken, starting out with ab initio calculations of the electronic structure of the complete concentration range range of the disordered binary Fe-C alloy. The mixing enthalpy of Fe-Cr has been quantitatively predicted and has, together with data from literature, been used in order to fit two sets of interatomic potentials for the purpose of simulating defect evolution with molecular dynamics and kinetic Monte-Carlo codes. These dedicated Fe-Cr alloy potentials are new and represent important additions to the pure element potentials that can be found in literature.
Energy Technology Data Exchange (ETDEWEB)
Wang, Yuezhong, E-mail: wyzphysics@163.com [Department of Physics and Key Laboratory for Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Tianjin Jinhang Institute of Technical Physics, Tianjin 300192 (China); Lu, Tiecheng, E-mail: lutiecheng@scu.edu.cn [Department of Physics and Key Laboratory for Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); International Center for Material Physics, Chinese Academy of Sciences, Shenyang 110015 (China); Zhang, Rongshi [Tianjin Jinhang Institute of Technical Physics, Tianjin 300192 (China); Jiang, Shengli; Qi, Jianqi; Wang, Ying [Department of Physics and Key Laboratory for Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Chen, Qingyun [Department of Physics and Key Laboratory for Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); National Defense Key Discipline Laboratory of Nuclear Waste and Environmental Safety, Southwest University of Science and Technology, Mianyang 621010 (China); Miao, Naihua [Physique Theorique des Materiaux, Universite de Liege, Sart Tilman B-4000 (Belgium); He, Duanwei [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610064 (China)
2013-01-25
Highlights: Black-Right-Pointing-Pointer We reassess the chemical bonding character of {gamma}-AlON which shows strong ionicity. Black-Right-Pointing-Pointer {gamma}-AlON single-crystals exhibit highly elastic anisotropy. Black-Right-Pointing-Pointer The thermodynamic properties are investigated in a wider temperature/pressure range. Black-Right-Pointing-Pointer {gamma}-AlON is an O/N partially disordered structure. - Abstract: Spinel aluminium oxynitride ({gamma}-AlON), as a kind of transparent ceramic material expectable, is studied using the ab initio density functional method, in terms of electronic, elastic, thermodynamic properties and structure disorder. The results show that {gamma}-AlON exhibits strong ionicity, as quantitatively expressed by (Al{sub O}{sup 2.43+}){sub 15}(Al{sub T}{sup 2.41+}){sub 8}(O{sup 1.64-}){sub 27}(N{sup 2.27-}){sub 5} from our reassessment of the ionic character. We summarize and speculate that the considered oxynitride single-crystals exhibit highly elastic anisotropy. The interpretation of the thermodynamic properties of {gamma}-AlON according to quasi-harmonic Debye model confirm the available experiments and are extended to a wider temperature/pressure range. This material holds high elastic strength under extreme environments, where dB/dT absolute value is less than 0.03 GPa/K, independent of the pressure. Finally, we study the O/N structure disorder character of {gamma}-AlON solid solution by investigating nine possible crystal structures. It is found that {gamma}-AlON should be partially disordered, and in fact, the O/N ordering has a significant effect on the properties.
International Nuclear Information System (INIS)
Wang, Yuezhong; Lu, Tiecheng; Zhang, Rongshi; Jiang, Shengli; Qi, Jianqi; Wang, Ying; Chen, Qingyun; Miao, Naihua; He, Duanwei
2013-01-01
Highlights: ► We reassess the chemical bonding character of γ-AlON which shows strong ionicity. ► γ-AlON single-crystals exhibit highly elastic anisotropy. ► The thermodynamic properties are investigated in a wider temperature/pressure range. ► γ-AlON is an O/N partially disordered structure. - Abstract: Spinel aluminium oxynitride (γ-AlON), as a kind of transparent ceramic material expectable, is studied using the ab initio density functional method, in terms of electronic, elastic, thermodynamic properties and structure disorder. The results show that γ-AlON exhibits strong ionicity, as quantitatively expressed by (Al O 2.43+ ) 15 (Al T 2.41+ ) 8 (O 1.64- ) 27 (N 2.27- ) 5 from our reassessment of the ionic character. We summarize and speculate that the considered oxynitride single-crystals exhibit highly elastic anisotropy. The interpretation of the thermodynamic properties of γ-AlON according to quasi-harmonic Debye model confirm the available experiments and are extended to a wider temperature/pressure range. This material holds high elastic strength under extreme environments, where dB/dT absolute value is less than 0.03 GPa/K, independent of the pressure. Finally, we study the O/N structure disorder character of γ-AlON solid solution by investigating nine possible crystal structures. It is found that γ-AlON should be partially disordered, and in fact, the O/N ordering has a significant effect on the properties.
Ab initio electronic stopping power in materials
International Nuclear Information System (INIS)
Shukri, Abdullah-Atef
2015-01-01
The average energy loss of an ion per unit path length when it is moving through the matter is named the stopping power. The knowledge of the stopping power is essential for a variety of contemporary applications which depend on the transport of ions in matter, especially ion beam analysis techniques and ion implantation. Most noticeably, the use of proton or heavier ion beams in radiotherapy requires the knowledge of the stopping power. Whereas experimental data are readily available for elemental solids, the data are much more scarce for compounds. The linear response dielectric formalism has been widely used in the past to study the electronic stopping power. In particular, the famous pioneering calculations due to Lindhard evaluate the electronic stopping power of a free electron gas. In this thesis, we develop a fully ab initio scheme based on linear response time-dependent density functional theory to predict the impact parameter averaged quantity named the random electronic stopping power (RESP) of materials without any empirical fitting. The purpose is to be capable of predicting the outcome of experiments without any knowledge of target material besides its crystallographic structure. Our developments have been done within the open source ab initio code named ABINIT, where two approximations are now available: the Random-Phase Approximation (RPA) and the Adiabatic Local Density Approximation (ALDA). Furthermore, a new method named 'extrapolation scheme' have been introduced to overcome the stringent convergence issues we have encountered. These convergence issues have prevented the previous studies in literature from offering a direct comparison to experiment. First of all, we demonstrate the importance of describing the realistic ab initio electronic structure by comparing with the historical Lindhard stopping power evaluation. Whereas the Lindhard stopping power provides a first order description that captures the general features of the
Bakkari, Karim; Fersi, Riadh; Kebir Hlil, El; Bessais, Lotfi; Thabet Mliki, Najeh
2018-03-01
First-principle calculations combining density functional theory and the full-potential linearized augmented plane wave (FP-LAPW) method are performed to investigate the electronic and magnetic structure of Pr2Co7 in its two polymorphic forms, (2:7 H) and (2:7 R), for the first time. This type of calculation was also performed for PrCo5 and PrCo2 intermetallics. We have computed the valence density of states separately for spin-up and spin-down states in order to investigate the electronic band structure. This is governed by the strong contribution of the partial DOS of 3d-Co bands compared to the partial DOS of the 4f-Pr bands. Such a high ferromagnetic state is discussed in terms of the strong spin polarization observed in the total DOS. The magnetic moments carried by the Co and Pr atoms located in several sites for all compounds are computed. These results mainly indicate that cobalt atoms make a dominant contribution to the magnetic moments. The notable difference in the atomic moments of Pr and Co atoms between different structural slabs is explained in terms of the magnetic characteristics of the PrCo2 and PrCo5 compounds and the local chemical environments of the Pr and Co atoms in different structural slabs of Pr2Co7. From spin-polarized calculations we have simulated the 3d and 4f band population to estimate the local magnetic moments. These results are in accordance with the magnetic moments calculated using the FP-LAPW method. In addition, the exchange interactions J ij are calculated and used as input for M(T) simulations. Involving the data obtained from the electronic structure calculations, the appropriate Padé Table is applied to simulate the magnetization M(T) and to estimate the mean-field Curie temperature. We report a fairly good agreement between the ab initio calculation of magnetization and Curie temperature with the experimental data.
Energy Technology Data Exchange (ETDEWEB)
Kong, Bo, E-mail: kong79@yeah.net, E-mail: yachao.zhang@pku.edu.cn [School of Physics and Electronic Sciences, Guizhou Education University, Guiyang 550018 (China); Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Education University, Guiyang 550018 (China); Zhang, Yachao, E-mail: kong79@yeah.net, E-mail: yachao.zhang@pku.edu.cn [Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Education University, Guiyang 550018 (China)
2016-07-07
The electronic structures of the cubic GdH{sub 3} are extensively investigated using the ab initio many-body GW calculations treating the Gd 4f electrons either in the core (4f-core) or in the valence states (4f-val). Different degrees of quasiparticle (QP) self-consistent calculations with the different starting points are used to correct the failures of the GGA/GGA + U/HSE03 calculations. In the 4f-core case, GGA + G{sub 0}W{sub 0} calculations give a fundamental band gap of 1.72 eV, while GGA+ GW{sub 0} or GGA + GW calculations present a larger band gap. In the 4f-val case, the nonlocal exchange-correlation (xc) functional HSE03 can account much better for the strong localization of the 4f states than the semilocal or Hubbard U corrected xc functional in the Kohn–Sham equation. We show that the fundamental gap of the antiferromagnetic (AFM) or ferromagnetic (FM) GdH{sub 3} can be opened up by solving the QP equation with improved starting point of eigenvalues and wave functions given by HSE03. The HSE03 + G{sub 0}W{sub 0} calculations present a fundamental band gap of 2.73 eV in the AFM configuration, and the results of the corresponding GW{sub 0} and GW calculations are 2.89 and 3.03 eV, respectively. In general, for the cubic structure, the fundamental gap from G{sub 0}W{sub 0} calculations in the 4f-core case is the closest to the real result. By G{sub 0}W{sub 0} calculations in the 4f-core case, we find that H or Gd defects can strongly affect the band structure, especially the H defects. We explain the mechanism in terms of the possible electron correlation on the hydrogen site. Under compression, the insulator-to-metal transition in the cubic GdH{sub 3} occurs around 40 GPa, which might be a satisfied prediction.
Ab initio studies of the electronic structure of Be93, Be105, Be111, and Be123 clusters
International Nuclear Information System (INIS)
Ross, R.B.; Kern, C.W.; Pitzer, R.M.; Ermler, W.C.
1995-01-01
Ab initio self-consistent-field calculations are reported for electronic states of beryllium clusters comprised of 93, 105, 111, and 123 atoms. The respective clusters correspond to coordination shells 12-15 of a central Be atom with internuclear separations derived from the lattice constants of the bulk metal. Ab initio effective core potentials have been employed to replace the 1s electrons, thereby reducing the complexity of the calculations. In addition, use of the full D 3h point group symmetry or the clusters results in a substantial reduction of the numbers of two-electron integrals that must be computed and processed. Binding energies, orbital energies, electric field gradient, nuclear-electrostatic potential, diamagnetic shielding constant, second moments, and Mulliken populations are calculated for selected electronic states. Calculated binding energies when compared among the different clusters as well as to smaller and larger fragments from earlier studies provide evidence for the onset of convergence to the Hartree-Fock limit of the bulk. Lowest-state ionization potentials are consistently above and agree to within 14% of the experimental workfunction. The net charge on the central beryllium atom decreases toward zero. The variability of observed bulklike behavior is not sharp and depends on the quantity of interest. 24 refs., 8 figs., 13 tabs
Bylaska, Eric J; Glaesemann, Kurt R; Felmy, Andrew R; Vasiliu, Monica; Dixon, David A; Tratnyek, Paul G
2010-11-25
Electronic structure methods were used to calculate the gas and aqueous phase reaction energies for reductive dechlorination (i.e., hydrogenolysis), reductive β-elimination, dehydrochlorination, and nucleophilic substitution by OH− of 1,2,3-trichloropropane. The thermochemical properties ΔH(f)°(298.15 K), S°(298.15 K, 1 bar), and ΔG(S)(298.15 K, 1 bar) were calculated by using ab initio electronic structure calculations, isodesmic reactions schemes, gas-phase entropy estimates, and continuum solvation models for 1,2,3-trichloropropane and several likely degradation products: CH3−CHCl−CH2Cl, CH2Cl−CH2−CH2Cl, C•H2−CHCl−CH2Cl, CH2Cl−C•H−CH2Cl, CH2═CCl−CH2Cl, cis-CHCl═CH−CH2Cl, trans-CHCl═CH−CH2Cl, CH2═CH−CH2Cl, CH2Cl−CHCl−CH2OH, CH2Cl−CHOH−CH2Cl, CH2═CCl−CH2OH, CH2═COH−CH2Cl, cis-CHOH═CH−CH2Cl, trans-CHOH═CH−CH2Cl, CH(═O)−CH2−CH2Cl, and CH3−C(═O)−CH2Cl. On the basis of these thermochemical estimates, together with a Fe(II)/Fe(III) chemical equilibrium model for natural reducing environments, all of the reactions studied were predicted to be very favorable in the standard state and under a wide range of pH conditions. The most favorable reaction was reductive β-elimination (ΔG(rxn)° ≈ −32 kcal/mol), followed closely by reductive dechlorination (ΔG(rxn)° ≈ −27 kcal/mol), dehydrochlorination (ΔG(rxn)° ≈ −27 kcal/mol), and nucleophilic substitution by OH− (ΔG(rxn)° ≈ −25 kcal/mol). For both reduction reactions studied, it was found that the first electron-transfer step, yielding the intermediate C•H2−CHCl−CH2Cl and the CH2Cl−C•H−CH2Cl species, was not favorable in the standard state (ΔG(rxn)° ≈ +15 kcal/mol) and was predicted to occur only at relatively high pH values. This result suggests that reduction by natural attenuation is unlikely.
International Nuclear Information System (INIS)
Nomura, Kenji; Ohta, Hiromichi; Hirano, Masahiro; Kamiya, Toshio; Uruga, Tomoya; Hosono, Hideo
2007-01-01
Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of ∼10 cm 2 V -1 s -1 [K. Nomura et al., Nature 488, 432 (2004)]. The local coordination structure in an IAOS, In-Ga-Zn-O (a-IGZO), was examined using extended x-ray absorption fine structure analysis combined with ab initio calculations. The short-range ordering and coordination structures in a-IGZO are similar to those in the corresponding crystalline phase, InGaZnO 4 , and edge-sharing structures consisting of In-O polyhedra remain in the amorphous structure. The In 3+ 5s orbitals form an extended state with a band effective mass of ∼0.2m e at the conduction band bottom
Energy Technology Data Exchange (ETDEWEB)
Bae, Gyun-Tack [Chungbuk National University, Cheongju (Korea, Republic of)
2016-05-15
We studied the structures and electronic properties of copper oxide clusters, Cu{sub 3}O{sub n} (n =1-6), using ab initio Monte Carlo simulations and density functional theory calculations. All lowest energy structures of neutral and charged Cu{sub 3}O{sub n} clusters with n =1-6 are optimized with the B3LYP functional and LANL2DZ basis set. We found that the lowest energy structures of neutral and charged Cu{sub 3}O{sub n} (n =1-6) clusters are planar or near-planar. Selected electronic properties including atomization energies, ionization energies, electron affinities, second difference in energies, HOMO - LUMO gaps, and Bader charges are calculated and examined for each n. We concluded that the Cu{sub 3}O{sub 3} cluster is the first ring structure and the most stable structure.
Ab Initio molecular dynamics with excited electrons
Alavi, A.; Kohanoff, J.; Parrinello, M.; Frenkel, D.
1994-01-01
A method to do ab initio molecular dynamics suitable for metallic and electronically hot systems is described. It is based on a density functional which is costationary with the finite-temperature functional of Mermin, with state being included with possibly fractional occupation numbers.
Ab initio electronic structure calculations for Mn linear chains deposited on CuN/Cu(001) surfaces
International Nuclear Information System (INIS)
Barral, Maria Andrea; Weht, Ruben; Lozano, Gustavo; Maria Llois, Ana
2007-01-01
In a recent experiment, scanning tunneling microscopy has been used to obtain a direct probe of the magnetic interaction in linear manganese chains arranged by atomic manipulation on thin insulating copper nitride islands grown on Cu(001). The local spin excitation spectra of these chains have been measured with inelastic electron tunneling spectroscopy. Analyzing the spectroscopic results with a Heisenberg Hamiltonian the interatomic coupling strength within the chains has been obtained. It has been found that the coupling strength depends on the deposition sites of the Mn atoms on the islands. In this contribution, we perform ab initio calculations for different arrangements of infinite Mn chains on CuN in order to understand the influence of the environment on the value of the magnetic interactions
DEFF Research Database (Denmark)
Shim, Irene; Baba, M. Sai; Gingerich, K.A.
2002-01-01
The low-lying states of the molecule Ge-2 and of the ion Ge-2(-) have been investigated by all electron ab initio multiconfiguration self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) calculations. The relativistic corrections for the Darwin contact term and for t......The low-lying states of the molecule Ge-2 and of the ion Ge-2(-) have been investigated by all electron ab initio multiconfiguration self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) calculations. The relativistic corrections for the Darwin contact term...... excited states are presented. Thermal functions based on the theoretically determined molecular parameters were used to derive the thermodynamic properties of the Ge-2 molecule from new mass spectrometric equilibrium data. The literature value for the dissociation energy of Ge-2 has been re...
Ab-initio study of the electronic structure of sup 1 sup 9 F implanted in GaAs and GaN crystals
Park, J H; Cho, H S; Shin, Y N
1998-01-01
We have studied the nuclear quadrupole interaction of a fluorine atom implanted in gallium arsenide and gallium nitride cluster models using the ab-initio Hartree-Fock theory. For the three possible fluorine sites in GaAs and GaN, we have determined the location of the implanted fluorine atom by using a self-consistent calculation, the electric field gradient at the implanted atom, and the electronic structure. Good agreement is found with experimental data wherever they are available. Predictions are made for the implanted fluorine site associated with the total energy and the electric field gradient which are expected to be measurable by a variety of experimental techniques.
Energy Technology Data Exchange (ETDEWEB)
Benrekia, A.R., E-mail: benrekia.ahmed@yahoo.com [Faculty of Science and Technology, University of Medea (Algeria); Benkhettou, N. [Laboratoire des Materiaux Magnetiques, Faculte des Sciences, Universite Djillali Liabes de Sidi Bel Abbes (Algeria); Nassour, A. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France); Driz, M. [Applied Material Laboratory (AML), Electronics Department, University of Sidi bel Abbes (DZ 22000) (Algeria); Sahnoun, M. [Laboratoire de Physique Quantique de la Matiere et Modelisations Mathematique (LPQ3M), Faculty of Science and Technology,University of Mascara (Algeria); Lebegue, S. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France)
2012-07-01
We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO{sub 3} and KTaO{sub 3}. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO{sub 3} and KTaO{sub 3}.
All-electron ab initio investigations of the electronic states of the NiC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl. A.
1999-01-01
The low-lying electronic states of NiC are investigated by all-electron ab initio multi-configuration self-consistent-field (CASSCF) calculations including relativistic corrections. The electronic structure of NiC is interpreted as perturbed antiferromagnetic couplings of the localized angular...
Ab initio calculations and modelling of atomic cluster structure
DEFF Research Database (Denmark)
Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.
2004-01-01
The optimized structure and electronic properties of small sodium and magnesium clusters have been investigated using it ab initio theoretical methods based on density-functional theory and post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system. A new theoretical...
International Nuclear Information System (INIS)
Pi, Xiaodong; Ni, Zhenyi; Yang, Deren; Delerue, Christophe
2014-01-01
In contrast to the conventional doping of bulk silicon (Si), the doping of Si nanocrystals (NCs) that are often smaller than 5 nm in diameter may lead to serious structural changes. Since the electronic and optical properties of Si NCs are intimately associated with their structures, it is critical to understand how doping impacts the structures of Si NCs. By means of ab initio calculation we now compare 1.4 nm phosphorus (P)-doped Si NCs without structural relaxation and those with structural relaxation. Structural changes induced by structural relaxation are manifested by the stretching and compressing of bonds and apparent variations in bond angles. With the increase of the concentration of P structural changes induced by structural relaxation become more serious. It is found that structural relaxation makes differences in the energy-level schemes of P-doped Si NCs. Structural relaxation also causes the binding energy of an electron in a P-doped Si NC to more significantly increase as the concentration of P increases. With the increase of the concentration of P structural relaxation leads to more pronounced changes in the optical absorption of P-doped Si NCs
International Nuclear Information System (INIS)
Zhou, Xiuquan; Gall, Daniel; Khare, Sanjay V.
2014-01-01
Highlights: • We use DFT to model the anti-ReO 3 structured transition metal nitrides M 3 N. • We predict their lattice constants, electronic structures and mechanical properties. • We correlate the metal d and nitrogen 2p orbitals with stability and hardness. • We established a high-throughput database for materials design. - Abstract: We report a systematic study of the anti-ReO 3 structured transition metal nitrides, M 3 N, using ab initio density functional theory computations in the local density approximation. Here M denotes all the 3d, 4d and 5d transition metals. Our calculations indicate that all M 3 N compounds except V 3 N of group 5 and Zn 3 N and Hg 3 N of group 12 are mechanically stable. For the stable M 3 N compounds, we report a database of predictions for their lattice constants, electronic properties and mechanical properties including bulk modulus, Young’s modulus, shear modulus, ductility, hardness and Debye temperature. It is found that most M 3 N compounds exhibit ductility with Vickers hardness between 0.4 GPa and 11.2 GPa. Our computed lattice constant for Cu 3 N, the only M 3 N compound where experiments exist, agrees well with the experimentally reported values. We report ratios of the melting points of all M 3 N compounds to that of Cu 3 N. The local density of states for all M 3 N compounds are obtained, and electronic band gaps are observed only for M of group 11 (Cu, Ag and Au) while the remaining M 3 N compounds are metallic without band gaps. Valence electron density along with the hybridization of the metal d and nitrogen 2p orbitals play an important role in determining the stability and hardness of different compounds. Our high-throughput databases for the cubic anti-ReO 3 structured transition metal nitrides should motivate future experimental work and shorten the time to their discovery
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, K. A.
1984-01-01
In the present study we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of the 2Sigma+ ground state as well as of 16 excited states of the RhC molecule. The calculated spectroscopic constants of the lowest lying states are in good agreement...... with the experimental data. The chemical bond in the electronic ground state is mainly due to interaction of the 4d orbitals of Rh with the 2s and 2p orbitals of C. The bond is a triple bond composed of two pi bonds and one sigma bond. The 5s electron of Rh hardly participates in the bond formation. It is located...
International Nuclear Information System (INIS)
Jezierski, Andrzej; Szytuła, Andrzej
2016-01-01
The electronic structures and thermodynamic properties of LaPtIn and CePtIn are studied by means of ab-initio full-relativistic full-potential local orbital basis (FPLO) method within densities functional (DFT) methodologies. We have also examined the influence of hydrogen on the electronic structure and stability of CePtInH and LaPtInH systems. The positions of the hydrogen atoms have been found from the minimum of the total energy. Our calculations have shown that band structure and topology of the Fermi surfaces changed significantly during the hydrogenation. The thermodynamic properties (bulk modulus, Debye temperatures, constant pressure heat capacity) calculated in quasi-harmonic Debye-Grüneisen model are in a good agreement with the experimental data. We have applied different methods of the calculation of the equation of states (EOS) (Murnaghan, Birch-Murnaghan, Poirier–Tarantola, Vinet). The thermodynamic properties are presented for the pressure 0< P<9 GPa and the temperature range 0< T<300 K. - Highlights: • Full relativistic band structure of LaPtIn and CePtIn. • Fermi surface of LaPtIn, LaPtInH, CePtIn, CePtInH. • Effect of hydrogenation on the electronic structure of LaPtIn and CePtIn. • Thermodynamic properties in the quasi-harmonic Debye-Grüneisen model.
Ab initio calculation of the electronic structure and spectroscopic properties of spinel γ-Sn3N4
International Nuclear Information System (INIS)
Ching, W. Y.; Rulis, Paul
2006-01-01
The electronic structure and physical properties of γ-Sn 3 N 4 in the spinel structure are investigated by first-principles calculations. The calculated band structure, electronic bonding, and optical properties are compared with two well-studied spinel nitrides γ-Si 3 N 4 and γ-Ge 3 N 4 . γ-Sn 3 N 4 is a semiconductor with a direct band gap of 1.40 eV and an attractive small electron effective mass of 0.17. Its optical properties are different from that of γ-Si 3 N 4 and γ-Ge 3 N 4 because of the difference in the conduction band minimum. The Sn K, Sn L 3 , Sn M 5 , and N K edges of the x-ray-absorption near-edge structure spectra in γ-Sn 3 N 4 are calculated using a supercell approach and are found to be rich in structures. These spectra are discussed in the context of the electronic structure of the unoccupied conduction band in the presence of the electron core-hole interaction. These calculated spectra can be used for the characterization of this novel compound
Czech Academy of Sciences Publication Activity Database
Šob, Mojmír; Kroupa, Aleš; Pavlů, Jana; Vřešťál, Jan
2009-01-01
Roč. 150, č. 1 (2009), s. 1-28 ISSN 1012-0394 R&D Projects: GA MŠk OC 147; GA ČR GA106/07/1078 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ab initio calculations * CALPHAD method * Laves phases * sigma phase * ternary systems * super-austenitic steels Subject RIV: BM - Solid Matter Physics ; Magnetism
International Nuclear Information System (INIS)
Wang, Y.; Lu, Y.H.; Wang, X.D.; Cao, Q.P.; Zhang, D.X.; Jiang, J.Z.
2014-01-01
Highlights: • The SOC effect affects the cohesion energy of crystal phase. • The effect of SOC was reduced due to random local atomic structures in liquids. • The local geometrical structures also affect the melting points. • Both SOC effect and local atomic structures are important for melting point difference. - Abstract: The origin of different melting points between Al 2 Cu and Al 2 Au has been studied using ab initio molecular dynamics simulations. Cohesive energy, electronic structures and structure information of both crystal and liquid phases have been analyzed. It is found that spin orbital coupling (SOC) plays an important role on the cohesive energy of crystal phase, consistent with the different melting points of these two alloys. Whereas, it seems that SOC has no effect on the formation energy and structure of liquid phase. Possible mechanism of reduced SOC effect at liquid phase is proposed. Our results are helpful to understand the glass formation ability difference between Al 2 Cu and Al 2 Au
Erkişi, Aytaç
2018-06-01
The quaternary full Heusler alloys FeMnCrSn and FeMnCrSb, which have face-centred cubic (FCC) crystal structure and conform to ? space group with 216 space number, have been investigated using Generalised Gradient Approximation (GGA) in the Density Functional Theory (DFT) as implemented in VASP (Vienna Ab initio Simulation Package) software. These alloys are considered in ferromagnetic (FM) order. After the investigation of structural stability of these alloys, their mechanical and thermal properties and also electronic band structures have been examined. The calculated spin-polarised electronic band structures and total electronic density of states (DOS) within GGA approximation show that these alloys can exhibit both metallic and half-metallic characters in different structural phases. The calculated formation enthalpies and the plotted energy-volume graphs show that Type-III phase is most stable structural phase for these materials. Also, FeMnCrSb alloy in Type-I/Type-III phases and FeMnCrSn alloy in Type-III phase show half-metallic behaviour with integer total magnetic moments almost 2 and 1 μB per formula unit, respectively, since there are band gaps observed in spin-down states, whereas they have metallic behaviour in majority bands. Other structural phases of both systems are also metallic. Moreover, the calculated elastic constants and the estimated anisotropy shear factors indicate that these materials are stable mechanically in all of three phases except FeMnCrSn in Type-I phase that does not satisfy Born stability criteria in this phase and have high anisotropic behaviour.
Structural distortion and electronic properties of NiO under high pressure: an ab initio GGA+U study
International Nuclear Information System (INIS)
Zhang Weibing; Hu Yulin; Han Keli; Tang Biyu
2006-01-01
The structural distortion and electronic properties of NiO under high pressure are investigated by means of first-principles calculations within the density functional theory (DFT) in the generalized gradient approximation (GGA). The strong electronic correlations are also taken into account in the form of GGA+U. Recent experiments implied that previous local density approximation (LDA) calculations incorrectly predicted structural distortion under high pressure, especially above 60 GPa. The present results show that even GGA calculations do not give a proper description of structural distortion under high pressure, although much improved structural and bulk properties are obtained. When strong correlations are included, overall agreement of the structural distortions of NiO under high pressure is obtained. The lattice constants a and c as well as the axial ratio c/a are in good agreement with experiment over the entire experimental pressure range. The successful prediction of the structural distortion of GGA+U can be attributed to the reasonable description of nearest-neighbour magnetic exchange interactions. In addition, we also analyse the density of states under different pressures. Present results indicate that, with increasing pressure, the bandwidth increases and the bandgap transits from being a mixture of charge-transfer and Mott-Hubbard type towards solely Mott-Hubbard type
Craco, L.; Laad, M. S.; Müller-Hartmann, E.
2003-12-01
Motivated by a study of various experiments describing the electronic and magnetic properties of the diluted magnetic semiconductor Ga1-xMnxAs, we investigate its physical response in detail using a combination of first-principles band structure with methods based on dynamical mean field theory to incorporate strong, dynamical correlations, and intrinsic as well as extrinsic disorder in one single theoretical picture. We show how ferromagnetism is driven by double exchange (DE), in agreement with very recent observations, along with a good quantitative description of the details of the electronic structure, as probed by scanning tunneling microscopy and optical conductivity. Our results show how ferromagnetism can be driven by DE even in diluted magnetic semiconductors with small carrier concentration.
Czech Academy of Sciences Publication Activity Database
Romanyuk, Olexandr; Supplie, O.; Susi, T.; May, M.M.; Hannappel, T.
2016-01-01
Roč. 94, č. 15 (2016), s. 1-9, č. článku 155309. ISSN 2469-9950 R&D Projects: GA ČR GF16-34856L Institutional support: RVO:68378271 Keywords : interface structure * GaP/Si heterointerface * interface electronic states * core- level shifts Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.836, year: 2016
Behzad, Somayeh
2016-09-01
Monolayer α-graphyne is a new two-dimensional carbon allotrope with many special features. In this work the electronic properties of AA- and AB-stacked bilayers of this material and then the optical properties are studied, using first principle plane wave method. The electronic spectrum has two Dirac cones for AA stacked bilayer α-graphyne. For AB-stacked bilayer, the interlayer interaction changes the linear bands into parabolic bands. The optical spectra of the most stable AB-stacked bilayer closely resemble to that of the monolayer, except for small shifts of peak positions and increasing of their intensity. For AB-stacked bilayer, a pronounced peak has been found at low energies under the perpendicular polarization. This peak can be clearly ascribed to the transitions at the Dirac point as a result of the small degeneracy lift in the band structure.
Mahatha, S K; Patel, K D; Menon, Krishnakumar S R
2012-11-28
Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS(2) and MoSe(2). The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS(2) to MoSe(2), the dispersion of the valence bands decreases along both k(parallel) and k(perpendicular), revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS(2) to MoSe(2).
Energy Technology Data Exchange (ETDEWEB)
Yadav, P. S.; Pandey, D. K., E-mail: pdhiraj2000@gmail.com; Agrawal, S.; Agrawal, B. K. [Allahabad University, Department of Physics (India)
2010-03-15
An ab initio study of the stability, structural, electronic. and optical properties has been performed for 46 zinc sulfide nanoclusters Zn{sub x}S{sub y} (x + y = n = 2 to 5). Five out of them are seen to be unstable as their vibrational frequencies are found to be imaginary. A B3LYP-DFT/6-311G(3df) method is employed to optimize the geometries and a TDDFT method is used for the study of the optical properties. The binding energies (BE), HOMO-LUMO gaps and the bond lengths have been obtained for all the clusters. For the ZnS{sub 2}, ZnS{sub 3}, and ZnS{sub 4} nanoclusters, our stable structures are seen to be different from those obtained earlier by using the effective core potentials. We have also considered the zero point energy (ZPE) corrections ignored by the earlier workers. For a fixed value of n, we designate the most stable structure the one, which has maximum final binding energy per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), charges on the atoms, dipole moments, optical properties, vibrational frequencies, infrared intensities, relative infrared intensities, and Raman scattering activities have been investigated for the most stable structures. The nanoclusters containing large number of S atoms for each n is found to be most stable. The HOMO-LUMO gap decreases from n = 2-3 and then increases above n = 3. The IP and EA both fluctuate with the cluster size n. The optical absorption is quite weak in visible region but strong in the ultraviolet region in most of the nanoclusters except a few. The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every nanocluster and may be used to characterize a specific nanocluster. The growth of most stable nanoclusters may be possible in the experiments.
Yadav, P. S.; Pandey, D. K.; Agrawal, S.; Agrawal, B. K.
2010-03-01
An ab initio study of the stability, structural, electronic. and optical properties has been performed for 46 zinc sulfide nanoclusters Zn x S y ( x + y = n = 2 to 5). Five out of them are seen to be unstable as their vibrational frequencies are found to be imaginary. A B3LYP-DFT/6-311G(3df) method is employed to optimize the geometries and a TDDFT method is used for the study of the optical properties. The binding energies (BE), HOMO-LUMO gaps and the bond lengths have been obtained for all the clusters. For the ZnS2, ZnS3, and ZnS4 nanoclusters, our stable structures are seen to be different from those obtained earlier by using the effective core potentials. We have also considered the zero point energy (ZPE) corrections ignored by the earlier workers. For a fixed value of n, we designate the most stable structure the one, which has maximum final binding energy per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), charges on the atoms, dipole moments, optical properties, vibrational frequencies, infrared intensities, relative infrared intensities, and Raman scattering activities have been investigated for the most stable structures. The nanoclusters containing large number of S atoms for each n is found to be most stable. The HOMO-LUMO gap decreases from n = 2-3 and then increases above n = 3. The IP and EA both fluctuate with the cluster size n. The optical absorption is quite weak in visible region but strong in the ultraviolet region in most of the nanoclusters except a few. The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every nanocluster and may be used to characterize a specific nanocluster. The growth of most stable nanoclusters may be possible in the experiments.
Structural, electronic, and mechanical properties of CoN and NiN. An ab initio study
Energy Technology Data Exchange (ETDEWEB)
Amudhavalli, A.; Manikandan, M.; Cinthia, A. Jemmy; Rajeswarapalanichamy, R. [NMSSVN College, Tamil Nadu (India). Dept. of Physics; Iyakutti, K. [SRM Univ., Tamil Nadu (India). Dept. of Physics and Nanotechnology
2017-07-01
The structural stabilities of cobalt mononitride (CoN) and nickel mono-nitride (NiN) were investigated among the crystal structures, namely, NaCl (B1), CsCl (B2), and zinc blende (B3). It was found that the zinc blende (B3) phase was the most stable phase for both nitrides. A pressure-induced structural phase transition from B3 to B1 phase was predicted in these nitrides. The computed lattice parameter values were in agreement with the experimental values and other theoretical values. The electronic structures reveal that these nitrides are metallic at zero pressure. The computed elastic constants indicate that CoN and NiN are mechanically stable in the B1 and B3 phases. The variations of the elastic constants, bulk modulus, shear modulus, Poisson's ratio, and elastic anisotropy factor with pressure were investigated. The Debye temperature θ{sub D} values are reported for both the nitrides in their B1 and B3 phases. The high-pressure NaCl phase of both CoN and NiN were found to be ferromagnetic.
Czech Academy of Sciences Publication Activity Database
Adler, R. W.; Allen, P. R.; Hnyk, Drahomír; Rankin, D. W. H.; Robertson, H. E.; Smart, B. A.; Gillespie, R. J.; Bytheway, I.
1999-01-01
Roč. 64, č. 12 (1999), s. 4226-4232 ISSN 0022-3263 Institutional research plan: CEZ:AV0Z4032918 Keywords : structure * initio calculations * 3,3-Diethylpentane Subject RIV: CC - Organic Chemistry Impact factor: 3.440, year: 1999
Directory of Open Access Journals (Sweden)
H A Badehian
2015-07-01
Full Text Available In recent work the structural, electronic and optical properties of BSb compound in bulk and surface (110 states have been studied. Calculations have been performed using Full-Potential Augmented Plane Wave (FP-LAPW method by WIEN2k code in Density Functional Theory (DFT framework. The structural properties of the bulk such as lattice constant, bulk module and elastic constants have been investigated using four different approximations. The band gap energy of the bulk and the (110 surface of BSb were obtained about 1.082 and 0.38 eV respectively. Moreover the surface energy, the work function, the surface relaxation, surface state and the band structure of BSb (110 were investigated using symmetric and stoichiometric 15 layers slabs with the vacuum of 20 Bohr. In addition, the real and imaginary parts of the dielectric function of the bulk and the BSb (110 slab were calculated and compared to each other. Our obtained results have a good agreement with the available results.
Ab-initio calculations of structural, electronic, and optical properties of Zn3(VO4)2
Ahmed, Nisar; Mukhtar, S.; Gao, Wei; Zafar Ilyas, Syed
2018-03-01
The structural, electronic, and optical properties of Zn3(VO4)2 are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT). Various approaches are adopted to treat the exchange and correlation potential energy such as generalized gradient approximation (GGA), GGA+U, and the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential. The calculated band gap of 3.424 eV by TB-mBJ is found to be close to the experimental result (3.3 eV). The optical anisotropy is analyzed through optical constants, such as dielectric function and absorption coefficient along parallel and perpendicular crystal orientations. The absorption coefficient reveals high absorption (1.5× {10}6 {cm}}-1) of photons in the ultraviolet region.
Mokhtari, Ali; Alidoosti, Mohammad
2014-11-01
In the present work, we have performed first principles calculations to study the structural and electronic properties of the MgFBrxCl1-x quaternary alloys using the pseudo-potential plane wave approach within the framework of density functional theory. By using the optimized initial parameters, we have obtained the physical quantities such as equilibrium lattice constants a and c, cohesive energy and band gap and then fitted the results by a quadratic expression for all x compositions. The results of bulk modulus exhibit nearly linear concentration dependence (LCD) but other quantities show nonlinear dependence. Finally, we have calculated the total and angular momentum decomposed (partial) density of states and determined the contributions of different orbitals of each atoms.
International Nuclear Information System (INIS)
Sharma, Sheetal; Verma, A.S.; Jindal, V.K.
2014-01-01
Graphical abstract: - Highlights: • FP-LAPW method has been used to compute the solid state properties of AgGaX 2 (X = S, Se, Te). • Electronic and optical properties reported with recently developed mBJ potential. • Thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter were evaluated. • Hardness was calculated for the first time at different temperature and pressure. - Abstract: We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of the silver gallium dichalcogenides (AgGaX 2 : X = S, Se, Te). In this study, we have used the accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the six elastic constants (C 11 , C 12 , C 13 , C 33 , C 44 and C 66 ). We have reported electronic and optical properties with the recently developed density functional theory of Tran and Blaha, and this theory is used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 40 eV. The thermodynamical properties such as thermal expansion, heat capacity, debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures (0–900 K) and pressures (0–8 GPa) and the silent results were interpreted. Hardness of the materials was calculated for the first time at different temperatures and pressures
International Nuclear Information System (INIS)
Honjou, Nobumitsu
2006-01-01
The energetics and electronic structure of the 1-5 2 Σ + and 1-3 2 Π states of CS + at and around the equilibrium internuclear distance R e for the CS X 1 Σ + state are studied by carrying out ab initio configuration interaction (CI) calculations. The spectroscopic constants of T e , ω e , and R e for the 1-4 2 Σ + , 1 2 Π, and 3 2 Π states are evaluated from the CI potential energy curves (PECs). The avoided crossing between the 2-3 2 Σ + PECs causes the 3 2 Σ + minimum and explains the observed high intensities for the photoionization from the CS X 1 Σ + state to both the 2-3 2 Σ + states. The avoided crossing between the 3-4 2 Σ + PECs produces the 3 2 Σ + maximum and 4 2 Σ + well minimum. The avoided crossing between the 2-3 2 Π PECs results in the 3 2 Π minimum and a small minimum spacing (0.14 eV) between the PECs
Endichi, A.; Zaari, H.; Benyoussef, A.; El Kenz, A.
2018-06-01
The magnetic behavior of LaCr2Si2C compound is investigated in this work, using first principle methods, Monte Carlo simulation (MCS) and mean field approximation (MFA). The structural, electronic and magnetic properties are described using ab initio method in the framework of the Generalized Gradient Approximation (GGA), and the Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method implemented in the WIEN2K packages. We have also computed the coupling terms between magnetic atoms which are used in Hamiltonian model. A theoretical study realized by mean field approximation and Monte Carlo Simulation within the Ising model is used to more understand the magnetic properties of this compound. Thereby, our results showed a ferromagnetic ordering of the Cr magnetic moments below the Curie temperature of 30 K (Tc magnetization, the energy, the specific heat and the susceptibility. This material shows the small sign of supra-conductivity; and future researches could be focused to enhance the transport and magnetic properties of this system.
Das, Uday; Naskar, Jishu; Mukherjee, Alok Kumar
2015-12-01
A terminally protected acyclic tetrapeptide has been synthesized, and the crystal structure of its hydrated form, Boc-Tyr-Aib-Tyr-Ile-OMe·2H2O (1), has been determined directly from powder X-ray diffraction data. The backbone conformation of tetrapeptide (1) exhibiting two consecutive β-turns is stabilized by two 4 → 1 intramolecular N-H · · · O hydrogen bonds. In the crystalline state, the tetrapeptide molecules are assembled through water-mediated O-H · · · O hydrogen bonds to form two-dimensional molecular sheets, which are further linked by intermolecular C-H · · · O hydrogen bonds into a three-dimensional supramolecular framework. The molecular electrostatic potential (MEP) surface of (1) has been used to supplement the crystallographic observations. The nature of intermolecular interactions in (1) has been analyzed quantitatively through the Hirshfeld surface and two-dimensional fingerprint plot. The DFT optimized molecular geometry of (1) agrees closely with that obtained from the X-ray structure analysis. The present structure analysis of Boc-Tyr-Aib-Tyr-Ile-OMe·2H2 O (1) represents a case where ab-initio crystal structure of an acyclic tetrapeptide with considerable molecular flexibility has been accomplished from laboratory X-ray powder diffraction data. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.
Energy Technology Data Exchange (ETDEWEB)
Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Laboratory, Department of Physics, Islamia College Peshawar (Pakistan); Gupta, S.K. [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Alahmed, Z.A. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Khachai, H. [Physics Department, Djillali Liabes University of Sidi Bel-Abbes (Algeria); Jha, P.K. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)
2014-06-01
Highlights: • REGa{sub 3} (RE = Sc or Lu) compounds are mechanical stabile. • Both ScGa{sub 3} and LuGa{sub 3} exhibit metallic behavior just like other REGa{sub 3} compounds. • Melting temperature T{sub m} (K) for ScGa{sub 3} and LuGa{sub 3} are 1244.2 and 1143.8. • High absorption observed in the visible energy region. • The present study would be helpful for future experimental/theoretical explorations. - Abstract: Structural, elastic, optoelectronic and thermodynamic properties of REGa{sub 3} (RE = Sc and Lu) compounds have been studied self consistently by employing state of the art full potential (FP) linearized (L) approach of augmented plane wave (APW) plus local orbitals method. Calculations were executed at the level of Perdew–Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA) for exchange correlation functional in addition to modified Becke–Johnson (mBJ) potential. Our obtained results of lattice parameters show reasonable agreement to the previously reported experimental and other theoretical studies. Analysis of the calculated band structure of ScGa{sub 3} and LuGa{sub 3} compounds demonstrates their metallic character. Moreover, a positive value of calculated Cauchy pressure, in addition to reflecting their ductile nature, endorses their metallic character as well. To understand optical behavior calculations related to the important optical parameters; real and imaginary parts of the dielectric function, reflectivity R(ω), refractive index n(ω) and electron energy-loss function L(ω) have also been performed. In the present work, thermodynamically properties are also investigated by employing lattice vibrations integrated in quasi harmonic Debye model. Obtained results of volume, heat capacity and Debye temperature as a function of temperature for both compounds, at different values of pressure, are found to be consistent. The calculated value of melting temperature for both compounds (ScGa{sub 3} and Lu
Energy Technology Data Exchange (ETDEWEB)
Pavloudis, Th. [Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece); Zervos, M. [Nanostructured Materials and Devices Laboratory, Department of Mechanical and Manufacturing Engineering, PO Box 20537, Nicosia 1678 (Cyprus); Komninou, Ph. [Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece); Kioseoglou, J., E-mail: sifisl@auth.gr [Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece)
2016-08-31
We carry out ab initio electronic structure calculations of (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} using density functional theory with projector augmented-wave potentials under the generalized gradient approximation. We find that the energetically favorable structure of Sn{sub 3}N{sub 4} is the face-centered cubic spinel structure, followed by the hexagonal structure which has energy band gaps of 1.85 eV and 1.44 eV respectively. The (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} ternary compound can exhibit both cubic and hexagonal crystal structures over the full range of x. However, the cubic structure is found to be energetically favorable for x < 0.3 above which the hexagonal structure of (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} dominates. The energy band gap can be tuned continuously from 1.44 eV up to 5.8 eV in the case of the hexagonal crystal structure of (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} and from 1.85 eV to 4.82 eV in the case of cubic (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4}. Nevertheless the energy gap of (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} is direct only for x < 0.3 when it is cubic and for x < 0.5 when hexagonal. - Highlights: • (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} exhibits both cubic and hexagonal crystal structures. • The cubic structure is favorable for x < 0.3 and the hexagonal structure for x > 0.3. • The bandgap of hexagonal (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4} may be tuned from 1.44 eV up to 5.8 eV. • The bandgap may be tuned from 1.85 eV to 4.82 eV for the cubic (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4}. • Bandgaps are direct for x < 0.3 (cubic) and for x < 0.5 3 (hexagonal (Si{sub x}Sn{sub 1−x}){sub 3}N{sub 4}).
Yildizhan, Gulsum; Caliskan, Serkan; Ozturk, Ramazan
2018-04-01
Nanoparticles composed of palladium and platinum are particularly interesting for catalytic purposes, for instance, selective hydrogenation and alcohol oxidation. The reactivity and selectivity of nanostructures are mostly based on the size and shape of the nanocrystals in catalytic reactions. In this work, we studied the structural stabilities of Pd and Pt based nanocubes and nanocages and adsorption strength of chemisorbed species on these nanostructures to investigate their structure dependent catalytic activities. Solid cubic and hollow cage like nanostructures of different sizes were designed with Pd and Pt atoms. The volume of the crystal cavity in nanocage structures was tuned by removing of atoms from solid cubic structure. The effect of size and shape on the formation energies and HOMO-LUMO energy gap of nanostructures were elucidated and correlated to structural stabilities, hardness-softness, electronegativity and electrophilicity index. The relationship between size and chemical reactivity clearly showed that increasing the number of atoms participating in a catalyst enhances the activity. For further understanding of the catalytic activity we employed 4-nitro thiophenol, as an S-donor representative molecule, to evaluate the adsorption characteristics of the nanostructures.
Sambathkumar, K; Jeyavijayan, S; Arivazhagan, M
2015-08-05
Combined experimental and theoretical studies were conducted on the molecular structure and vibrational spectra of 4-AminoPhthalhydrazide (APH). The FT-IR and FT-Raman spectra of APH were recorded in the solid phase. The molecular geometry and vibrational frequencies of APH in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking 6-311+G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF and B3LYP method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of APH with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the NMR spectra of APH was also reported. The theoretical spectrograms for infrared and Raman spectra of the title molecule have been constructed. UV-vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. And the temperature dependence of the thermodynamic properties of constant pressure (Cp), entropy (S) and enthalpy change (ΔH0→T) for APH were also determined. Copyright © 2015 Elsevier B.V. All rights reserved.
Ab initio calculation of electronic structure and magnetic properties of R2Fe14BNx (R = Pr,Nd)
Tian, Guang; Zha, Liang; Yang, Wenyun; Qiao, Guanyi; Wang, Changsheng; Yang, Yingchang; Yang, Jinbo
2018-05-01
The site preference of N atom for R2Fe14BNx (R= Pr, Nd) and the interstitial nitrogen effect on the magnetic properties have been studied by the first-principles method. It was found that the nitrogen is more likely to occupy the 4e site for Pr2Fe14BNx compound, while 4f site for Nd2Fe14BNx. When N atoms entering some specific crystal sites (such as 2a and 4f), the total magnetic moments of these compounds are not reduced, but slightly increased. Although the doping of N may reduce the total magnetic moments of some R2Fe14B compounds in the cases of optimal occupancy, the volumetric effect caused by N doping can still change the electron density distributions of Fe near the Fermi level, improving the magnetic ordering temperature of such compounds.
Energy Technology Data Exchange (ETDEWEB)
Matar, Samir F. [CNRS, ICMCB, UPR 9048, Pessac (France); Bordeaux Univ., Pessac (France). ICMCB, UPR 9048; Al Alam, Adel F.; Ouaini, Naim [Univ. Saint Esprit de Kaslik (USEK), Jounieh (Lebanon). URA GREVE, CSR-USEK
2013-01-15
For equiatomic MgNi which can be hydrogenated up to the composition MgNiH{sub 1.6} at an absorption/desorption temperature of 200 C, the effects of hydrogen absorption are approached with the model structures MgNiH, MgNiH{sub 2} and MgNiH{sub 3}. From full geometry optimization and calculated cohesive energies obtained within DFT, the MgNiH{sub 2} composition close to the experimental limit is identified as most stable. Charge density analysis shows an increasingly covalent character of hydrogen: MgNiH(H{sup -0.67}) {yields} MgNiH{sub 2}(H{sup -0.63}) {yields} MgNiH{sub 3}(H{sup -0.55}). While Mg-Ni bonding prevails in MgNi and hydrogenated model phases, extra itinerant low-energy Ni states appear when hydrogen is introduced signaling Ni-H bonding which prevails over Mg-H as evidenced from total energy calculations and chemical bonding analyses. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Dannenberg, Antje
2011-08-30
The mechanism which causes many of the unusual thermomechanical properties of martensitic alloys, as for example, superelasticity and the shape-memory effect, is the martensitic transformation. The prototype ferromagnetic shape memory alloy (FSMA) is Ni{sub 2}MnGa. But a technological breakthrough is missing due to its poor ductility and low operation temperatures. The goal of this thesis is the proposal of new FSMA appropriate for future technological applications. I focus on X{sub 2}YZ Heusler alloys which are mainly based on Mn, Fe, Co, and Ni for the X and Y sites and Z=Ga or Zn. The big challenge of this work is to find material classes which combine the unique magnetomechanical properties of FSMA which are large recoverable magnetostrictive strains, high magnetocrystalline anisotropy energy, and highly mobile twin boundaries with transformation temperatures clearly above room temperature and a reduced brittleness. Such a study, providing material classes which from a theoretical point of view are promising candidates for future FSMA, will help the experimental physicists to select interesting subgroups in the vast number of possible chemical compositions of X{sub 2}YZ Heusler alloys. I have systematically varied the composition in the new Heusler alloys in order to find trends indicating generic tendencies of the material properties, for instance, as a function of the valence electron concentration e/a. A main feature of this thesis is the attempt to find the origin of the competing structural ordering tendencies between conventional X{sub 2}YZ and inverse (XY)XZ Heusler structures which are observed for all systems investigated. In the first part of this work the accuracy and predictive power of ab initio and Monte Carlo simulations is demonstrated by reproducing the experimental phase diagram of Ni-Mn-(Ga,In,Sn,Sb). The linear increasing and decreasing slopes of T{sub M} and T{sub C} can be reproduced by total and free energy calculations and the analysis
Ab Initio Nuclear Structure and Reaction Calculations for Rare Isotopes
Energy Technology Data Exchange (ETDEWEB)
Draayer, Jerry P. [Louisiana State Univ., Baton Rouge, LA (United States)
2014-09-28
We have developed a novel ab initio symmetry-adapted no-core shell model (SA-NCSM), which has opened the intermediate-mass region for ab initio investigations, thereby providing an opportunity for first-principle symmetry-guided applications to nuclear structure and reactions for nuclear isotopes from the lightest p-shell systems to intermediate-mass nuclei. This includes short-lived proton-rich nuclei on the path of X-ray burst nucleosynthesis and rare neutron-rich isotopes to be produced by the Facility for Rare Isotope Beams (FRIB). We have provided ab initio descriptions of high accuracy for low-lying (including collectivity-driven) states of isotopes of Li, He, Be, C, O, Ne, Mg, Al, and Si, and studied related strong- and weak-interaction driven reactions that are important, in astrophysics, for further understanding stellar evolution, X-ray bursts and triggering of s, p, and rp processes, and in applied physics, for electron and neutrino-nucleus scattering experiments as well as for fusion ignition at the National Ignition Facility (NIF).
Ab Initio Nuclear Structure and Reaction Calculations for Rare Isotopes
International Nuclear Information System (INIS)
Draayer, Jerry P.
2014-01-01
We have developed a novel ab initio symmetry-adapted no-core shell model (SA-NCSM), which has opened the intermediate-mass region for ab initio investigations, thereby providing an opportunity for first-principle symmetry-guided applications to nuclear structure and reactions for nuclear isotopes from the lightest p-shell systems to intermediate-mass nuclei. This includes short-lived proton-rich nuclei on the path of X-ray burst nucleosynthesis and rare neutron-rich isotopes to be produced by the Facility for Rare Isotope Beams (FRIB). We have provided ab initio descriptions of high accuracy for low-lying (including collectivity-driven) states of isotopes of Li, He, Be, C, O, Ne, Mg, Al, and Si, and studied related strong- and weak-interaction driven reactions that are important, in astrophysics, for further understanding stellar evolution, X-ray bursts and triggering of s, p, and rp processes, and in applied physics, for electron and neutrino-nucleus scattering experiments as well as for fusion ignition at the National Ignition Facility (NIF).
Ab initio study of hot electrons in GaAs
Bernardi, Marco; Vigil-Fowler, Derek; Ong, Chin Shen; Neaton, Jeffrey B.; Louie, Steven G.
2015-01-01
Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation...
Energy Technology Data Exchange (ETDEWEB)
Neef, Matthias
2007-03-19
Aim of this thesis was to reach by a systematic study of different ab initio procedures an improved description of the electronic properties of FeSi and FeGe. Central result is the itinerant description of FeSi as a semiconductor in the neighbourhood of a ferromagnetic instability. The regardment of the nonlocal exchange in the effective one-particle approximation leads to a metastable magnetic state scarcely above the magnetic ground state. The application of the hybrid functional leads to a 1st order metal-isolator transition for large lattice parameters: FeSi transforms at increasement of the lattice parameter from an unmagnetic isolator to a magnetic metal. A similar behavior is found in the isostructural compound FeGe. The two systems FeSi and FeGe were systematically and detailedly analyzed by means of ab initio procedures. Thereby the structural, electronic, and magnetic properties were studied with DFT and HF calculations. Both calculations with spin polarization and without spin polarization were performed.
International Nuclear Information System (INIS)
Marshall, T.S.; Wilson, T.M.
1992-01-01
The authors report on the results of electronic band structure calculations of bulk ZnSe, bulk ZnS and the (ZnSe) 1 (ZnS) 1 , strained-layer superlattice (SLS) using the ab initio factorized linear combination of atomic orbitals method. The bulk calculations were done using the standard primitive nonrectangular 2-atom zinc blende unit cell, while the SLS calculation was done using a primitive tetragonal 4-atom unit cell modeled from the CuAu I structure. The analytic fit to the SLS crystalline potential was determined by using the nonlinear coefficients from the bulk fits. The CPU time saved by factorizing the energy matrix integrals and using a rectangular unit cell is discussed
Directory of Open Access Journals (Sweden)
S. J Hashemifar
2015-01-01
Full Text Available In this paper, the structural, magnetic, and electronic properties of two- to nine-atom copper and silver clusters and their alloys with one palladium atom are investigated by using full-potential all-electron density functional computations. After calculating minimized energy of several structural isomers of every nanocluster, it is argued that the small size nanoclusters (up to size of 6, prefer planar structures, while by increasing size a 2D-3D structural transformation is observed. The structural transformation of pure and copper-palladium clusters occurs in the size of seven and that of silver-palladium cluster in happens at the size of six. The calculated second difference and dissociation energies confirm that the two- and eight- atom pure clusters and three- and seven- atom alloyed clusters are magic clusters. The electronic and magnetic properties of stable isomers are calculated and considered after applying many body based GW correction.
Suturina, Elizaveta A; Nehrkorn, Joscha; Zadrozny, Joseph M; Liu, Junjie; Atanasov, Mihail; Weyhermüller, Thomas; Maganas, Dimitrios; Hill, Stephen; Schnegg, Alexander; Bill, Eckhard; Long, Jeffrey R; Neese, Frank
2017-03-06
The magnetic properties of pseudotetrahedral Co(II) complexes spawned intense interest after (PPh 4 ) 2 [Co(SPh) 4 ] was shown to be the first mononuclear transition-metal complex displaying slow relaxation of the magnetization in the absence of a direct current magnetic field. However, there are differing reports on its fundamental magnetic spin Hamiltonian (SH) parameters, which arise from inherent experimental challenges in detecting large zero-field splittings. There are also remarkable changes in the SH parameters of [Co(SPh) 4 ] 2- upon structural variations, depending on the counterion and crystallization conditions. In this work, four complementary experimental techniques are utilized to unambiguously determine the SH parameters for two different salts of [Co(SPh) 4 ] 2- : (PPh 4 ) 2 [Co(SPh) 4 ] (1) and (NEt 4 ) 2 [Co(SPh) 4 ] (2). The characterization methods employed include multifield SQUID magnetometry, high-field/high-frequency electron paramagnetic resonance (HF-EPR), variable-field variable-temperature magnetic circular dichroism (VTVH-MCD), and frequency domain Fourier transform THz-EPR (FD-FT THz-EPR). Notably, the paramagnetic Co(II) complex [Co(SPh) 4 ] 2- shows strong axial magnetic anisotropy in 1, with D = -55(1) cm -1 and E/D = 0.00(3), but rhombic anisotropy is seen for 2, with D = +11(1) cm -1 and E/D = 0.18(3). Multireference ab initio CASSCF/NEVPT2 calculations enable interpretation of the remarkable variation of D and its dependence on the electronic structure and geometry.
All electron ab initio investigations of the electronic states of the FeC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
1999-01-01
The low lying electronic states of the molecule FeC have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) and multi reference configuration interaction (MRCI) calculations. The relativistic corrections for the one electron Darwin contact term...
All Electron ab initio Investigations of the Electronic States of the MoN Molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
1999-01-01
The low lying electronic states of the molecule MoN have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction have...
An ab-initio study of mechanical, dynamical and electronic properties of MgEu intermetallic
Kumar, S. Ramesh; Jaiganesh, G.; Jayalakshmi, V.
2018-04-01
The theoretical investigation on the mechanical, dynamical and electronic properties of MgEu in CsCl-type structure has been carried out through the ab-initio calculations within the framework of the density functional theory and the density functional perturbation theory. For the purpose, Vienna Ab initio Simulation Package and Phonopy packages were used. Our calculated ground-state properties of MgEu are in good agreement with other available results. Our computed elastic constants and phonon spectrum results suggest that MgEu is mechanically and dynamically stable up to 5 GPa. The thermodynamic quantities as a function of temperatures are also reported and discussed. The band structure, density of states and charge density also calculated to understand the electronic properties of MgEu.
Instructional Approach to Molecular Electronic Structure Theory
Dykstra, Clifford E.; Schaefer, Henry F.
1977-01-01
Describes a graduate quantum mechanics projects in which students write a computer program that performs ab initio calculations on the electronic structure of a simple molecule. Theoretical potential energy curves are produced. (MLH)
DEFF Research Database (Denmark)
Shim, Irene; Kingcade, Joseph E. , Jr.; Gingerich, Karl A.
1986-01-01
In the present work we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of six electronic states of the PdGe molecule. The molecule is predicted to have a 3Pi ground state and two low-lying excited states 3Sigma− and 1Sigma+. The electronic structure...
Fleischer, Holger; Wann, Derek A; Hinchley, Sarah L; Borisenko, Konstantin B; Lewis, James R; Mawhorter, Richard J; Robertson, Heather E; Rankin, David W H
2005-10-07
The molecular structures of Se(SCH(3))(2) and Te(SCH(3))(2) were investigated using gas-phase electron diffraction (GED) and ab initio and DFT geometry optimisations. While parameters involving H atoms were refined using flexible restraints according to the SARACEN method, parameters that depended only on heavy atoms could be refined without restraints. The GED-determined geometric parameters (r(h1)) are: rSe-S 219.1(1), rS-C 183.2(1), rC-H 109.6(4) pm; angleS-Se-S 102.9(3), angleSe-S-C 100.6(2), angleS-C-H (mean) 107.4(5), phiS-Se-S-C 87.9(20), phiSe-S-C-H 178.8(19) degrees for Se(SCH(3))(2), and rTe-S 238.1(2), rS-C 184.1(3), rC-H 110.0(6) pm; angleS-Te-S 98.9(6), angleTe-S-C 99.7(4), angleS-C-H (mean) 109.2(9), phiS-Te-S-C 73.0(48), phiTe-S-C-H 180.1(19) degrees for Te(SCH(3))(2). Ab initio and DFT calculations were performed at the HF, MP2 and B3LYP levels, employing either full-electron basis sets [3-21G(d) or 6-31G(d)] or an effective core potential with a valence basis set [LanL2DZ(d)]. The best fit to the GED structures was achieved at the MP2 level. Differences between GED and MP2 results for rS-C and angleS-Te-S were explained by the thermal population of excited vibrational states under the experimental conditions. All theoretical models agreed that each compound exists as two stable conformers, one in which the methyl groups are on the same side (g(+)g(-) conformer) and one in which they are on different sides (g(+)g(+) conformer) of the S-Y-S plane (Y = Se, Te). The conformational composition under the experimental conditions could not be resolved from the GED data. Despite GED R-factors and ab initio and DFT energies favouring the g(+)g(+) conformer, it is likely that both conformers are present, for Se(SCH(3))(2) as well as for Te(SCH(3))(2).
Ab initio methods for electron-molecule collisions
International Nuclear Information System (INIS)
Collins, L.A.; Schneider, B.I.
1987-01-01
This review concentrates on the recent advances in treating the electronic aspect of the electron-molecule interaction and leaves to other articles the description of the rotational and vibrational motions. Those methods which give the most complete treatment of the direct, exchange, and correlation effects are focused on. Such full treatments are generally necessary at energies below a few Rydbergs (≅ 60 eV). This choice unfortunately necessitates omission of those active and vital areas devoted to the development of model potentials and approximate scattering formulations. The ab initio and model approaches complement each other and are both extremely important to the full explication of the electron-scattering process. Due to the rapid developments of recent years, the approaches that provide the fullest treatment are concentrated on. 81 refs
Energy Technology Data Exchange (ETDEWEB)
Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, Ibn Khaldoun University of Tiaret, Postbox 78-Zaaroura, 14000 Tiaret (Algeria); Abdiche, A.; Riane, R. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria)
2014-03-01
In this work, we present a density-functional theory study of structural, electronic and optical properties of BAs, BN binary compounds and their ternary BN{sub x}As{sub 1−x} solid solutions. The calculations are done by using the all-electron full potential linear augmented plane-wave method (FP-LAPW) as employed in WIEN2k code. For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The electronic band structure of these compounds have been calculated by using the above two approximations. We have also investigated in this article the density of state and the optical properties such as the dielectric function and the refractive index of BAs, BN and BN{sub 0.25}As{sub 0.75} compounds by using the above method. The results obtained for structural and electronic properties are compared with experimental data and other computational work. It has been found that the energy bands with all these approximations are similar except the band gap values. It has also been found that our results with LDA and GGA are in good agreement with other computational work wherever these are available.
Ab initio molecular crystal structures, spectra, and phase diagrams.
Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni
2014-09-16
Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling
Energy Technology Data Exchange (ETDEWEB)
Wang, Y. [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Lu, Y.H., E-mail: luyh@zju.edu.cn [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Wang, X.D.; Cao, Q.P. [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Zhang, D.X. [State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027 (China); Jiang, J.Z., E-mail: jiangjz@zju.edu.cn [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)
2014-11-15
Highlights: • The SOC effect affects the cohesion energy of crystal phase. • The effect of SOC was reduced due to random local atomic structures in liquids. • The local geometrical structures also affect the melting points. • Both SOC effect and local atomic structures are important for melting point difference. - Abstract: The origin of different melting points between Al{sub 2}Cu and Al{sub 2}Au has been studied using ab initio molecular dynamics simulations. Cohesive energy, electronic structures and structure information of both crystal and liquid phases have been analyzed. It is found that spin orbital coupling (SOC) plays an important role on the cohesive energy of crystal phase, consistent with the different melting points of these two alloys. Whereas, it seems that SOC has no effect on the formation energy and structure of liquid phase. Possible mechanism of reduced SOC effect at liquid phase is proposed. Our results are helpful to understand the glass formation ability difference between Al{sub 2}Cu and Al{sub 2}Au.
Klaa, K.; Labidi, S.; Masrour, R.; Jabar, A.; Labidi, M.; Amara, A.; Drici, A.; Hlil, E. K.; Ellouze, M.
2018-06-01
Structural, electronic, magnetic and thermodynamic main features for Ni1-xTixO ternary alloys in rock-salt structure with Ti content in the range ? were studied using the full potential Linearized augmented plane wave (FP-LAPW) method within density functional theory. The exchange-correlation potential was calculated by the generalized gradient approximation. The analysis of the electronic density of states curves allowed the computation of the magnetic moments which are considered to lie along (010) axes. The thermodynamic stability of this alloy was investigated by calculating the excess enthalpy of mixing ? as well as the phase diagram. In addition, the Monte Carlo simulations have been exploited to calculate the transition temperature and magnetic coercive field in the alloy.
International Nuclear Information System (INIS)
Nahif, F; Music, D; Mráz, S; To Baben, M; Schneider, J M
2013-01-01
Using density functional theory, the effect of Si on the stability and electronic structure of γ- and α-Al 2 O 3 has been investigated. The concentration range from 0 to 5 at.% is probed and the additive is positioned at different substitutional sites in the γ-phase. The calculations for (Al,Si) 2 O 3 predict a trend towards spontaneous decomposition into α-/γ-Al 2 O 3 and SiO 2 . Therefore, the formation of the metastable γ-(Al,Si) 2 O 3 phase can only be expected during non-equilibrium processing where the decomposition is kinetically hindered. The Si-induced changes in stability of this metastable solid solution may be understood based on the electronic structure. As the Si concentration is increased, stiff silicon–oxygen bonds are formed giving rise to the observed stabilization of the γ-phase. (paper)
Ab Initio Analysis of Auger-Assisted Electron Transfer.
Hyeon-Deuk, Kim; Kim, Joonghan; Prezhdo, Oleg V
2015-01-15
Quantum confinement in nanoscale materials allows Auger-type electron-hole energy exchange. We show by direct time-domain atomistic simulation and analytic theory that Auger processes give rise to a new mechanism of charge transfer (CT) on the nanoscale. Auger-assisted CT eliminates the renown Marcus inverted regime, rationalizing recent experiments on CT from quantum dots to molecular adsorbates. The ab initio simulation reveals a complex interplay of the electron-hole and charge-phonon channels of energy exchange, demonstrating a variety of CT scenarios. The developed Marcus rate theory for Auger-assisted CT describes, without adjustable parameters, the experimental plateau of the CT rate in the region of large donor-acceptor energy gap. The analytic theory and atomistic insights apply broadly to charge and energy transfer in nanoscale systems.
Energy Technology Data Exchange (ETDEWEB)
Marquez, A.; Sanz, J.F. (Universidad de Sevilla (Spain))
1992-12-02
Experimental and theoretical research on the electronic and geometric structure of transition-metal-carbenes and -alkylidenes is an active area in chemistry nowadays due to their potential activity in catalysis and in organic and organometallic synthesis. A theoretical investigation of the electronic structure of the high-valent, transition-metal, alkylidene-like complexes MoM[prime]H[sub 2] (M[prime] = C, Si, Ge, and Sn) is reported. Based on ab initio calculations carried out at the complete active space multiconfiguration self-consistent field (CASSCF) level, the molecular structure of the ground state and some low-lying excited states have been determined. For M[prime] = C, Si, and Ge, the ground state has C[sub 2v] symmetry (state [sup 5]B[sub 1]) and corresponds to pairing each electron of the M[prime]H[sub 2] triplet [sup 3]B[sub 1] with an electron of Mo ([sup 7]S). In the case of MoSnH[sub 2], the lowest state is bent (C[sub s] symmetry, state [sup 7]A[prime]), the out-of-plane angle being 68[degrees], and dissociates into SnH[sub 2] ([sup 1]A[sub 1]) + Mo ([sup 7]S). Dissociation energies, potential energy profiles for the dissociation, harmonic force constants in terms of internal symmetry coordinates, and vibrational frequencies are reported. The comparison of these properties with those of their pentacarbonylated homologous (CO)[sub 5]M[double bond]M[prime]H[sub 2] shows that the carbene-like (Fischer) type of complexation is stronger than the alkylidene-like one (Schrock). 28 refs., 4 figs., 6 tabs.
International Nuclear Information System (INIS)
Dos Santos, Renato B; Mota, F de Brito; Rivelino, R; Kakanakova-Georgieva, A; Gueorguiev, G K
2016-01-01
Graphite-like hexagonal AlN (h-AlN) multilayers have been experimentally manifested and theoretically modeled. The development of any functional electronics applications of h-AlN would most certainly require its integration with other layered materials, particularly graphene. Here, by employing vdW-corrected density functional theory calculations, we investigate structure, interaction energy, and electronic properties of van der Waals stacking sequences of few-layer h-AlN with graphene. We find that the presence of a template such as graphene induces enough interlayer charge separation in h-AlN, favoring a graphite-like stacking formation. We also find that the interface dipole, calculated per unit cell of the stacks, tends to increase with the number of stacked layers of h-AlN and graphene. (paper)
Ab initio study of structural, electronic and optical properties of MnHg(SCN)4 and FeHg(SCN)4
International Nuclear Information System (INIS)
He, K.H.; Zheng, G.; Chen, G.; Lue, T.; Wan, M.; Ji, G.F.
2007-01-01
The structural, electronic and optical properties of MnHg(SCN) 4 and FeHg(SCN) 4 were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN) 4 have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN) 4 . The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN) 4 lag behind those of MnHg(SCN) 4 and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena
Tomonari, Mutsumi; Nagashima, Umpei; Hirano, Tsuneo
2009-04-01
Electronic structures and molecular constants of the ground ∑7+ and low-lying A 7Π and a ∑5+ electronic excited states of the MnH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI) with Davidson's correction (+Q) calculations under exact C∞v symmetry using Slater-type basis sets. To correctly describe the ∑7+ electronic ground state, X ∑7+, at the MR-SDCI+Q calculation, we employed a large number of reference configurations in terms of the state-averaged complete active space self-consistent field (CASSCF) orbitals, taking into account the contribution from the B ∑7+ excited state. The A 7Π and a ∑5+ states can well be described by the MR-SDCI wave functions based on the CASSCF orbitals obtained for the lowest state only. In the MR-SDCI+Q, calculations of the X ∑7+, A 7Π, and a ∑5+ states required 16, 7, and 17 reference configurations, respectively. Molecular constants, i.e., re and ωe of these states and excitation energy from the X ∑7+ state, obtained at the MR-SDCI+Q level, showed a good agreement with experimental values. The small remaining differences may be accounted for by taking relativistic effects into account.
Tomonari, Mutsumi; Nagashima, Umpei; Hirano, Tsuneo
2009-04-21
Electronic structures and molecular constants of the ground (7)Sigma(+) and low-lying A (7)Pi and a (5)Sigma(+) electronic excited states of the MnH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI) with Davidson's correction (+Q) calculations under exact C(infinity v) symmetry using Slater-type basis sets. To correctly describe the (7)Sigma(+) electronic ground state, X (7)Sigma(+), at the MR-SDCI+Q calculation, we employed a large number of reference configurations in terms of the state-averaged complete active space self-consistent field (CASSCF) orbitals, taking into account the contribution from the B (7)Sigma(+) excited state. The A (7)Pi and a (5)Sigma(+) states can well be described by the MR-SDCI wave functions based on the CASSCF orbitals obtained for the lowest state only. In the MR-SDCI+Q, calculations of the X (7)Sigma(+), A (7)Pi, and a (5)Sigma(+) states required 16, 7, and 17 reference configurations, respectively. Molecular constants, i.e., r(e) and omega(e) of these states and excitation energy from the X (7)Sigma(+) state, obtained at the MR-SDCI+Q level, showed a good agreement with experimental values. The small remaining differences may be accounted for by taking relativistic effects into account.
Energy Technology Data Exchange (ETDEWEB)
He, K.H. [College of Maths and Physics, China University of Geosciences, Wuhan 430074 (China)]. E-mail: he23981006@126.com; Zheng, G. [College of Maths and Physics, China University of Geosciences, Wuhan 430074 (China)]. E-mail: gzheng25@yahoo.com; Chen, G. [College of Maths and Physics, China University of Geosciences, Wuhan 430074 (China); Lue, T. [College of Maths and Physics, China University of Geosciences, Wuhan 430074 (China); Wan, M. [College of Maths and Physics, China University of Geosciences, Wuhan 430074 (China); Ji, G.F. [Laboratory for Shock Wave and Detonation Physics, China Academy of Engineering Physics, Mianyang 621900 (China)
2007-03-01
The structural, electronic and optical properties of MnHg(SCN){sub 4} and FeHg(SCN){sub 4} were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN){sub 4} have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN){sub 4}. The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN){sub 4} lag behind those of MnHg(SCN){sub 4} and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena.
Electronic properties of liquid Hg-In alloys : Ab-initio molecular dynamics study
International Nuclear Information System (INIS)
Sharma, Nalini; Ahluwalia, P. K.; Thakur, Anil
2016-01-01
Ab-initio molecular dynamics simulations are performed to study the structural properties of liquid Hg-In alloys. The interatomic interactions are described by ab-initio pseudopotentials given by Troullier and Martins. Three liquid Hg-In alloys (Hg_1_0In_9_0, Hg_3_0In_7_0_,_. Hg_5_0In_5_0, Hg_7_0In_3_0, and Hg_9_0Pb_1_0) at 299 K are considered. The calculated results for liquid Hg (l-Hg) and lead (l-In) are also drawn. Along with the calculated results of considered five liquid alloys of Hg-In alloy. The results obtained from electronic properties namely total density of state and partial density of states help to find the local arrangement of Hg and In atoms and the presence of liquid state in the considered five alloys.
Ab initio theoretical calculations of the electronic excitation energies of small water clusters.
Tachikawa, Hiroto; Yabushita, Akihiro; Kawasaki, Masahiro
2011-12-14
A direct ab initio molecular dynamics method has been applied to a water monomer and water clusters (H(2)O)(n) (n = 1-3) to elucidate the effects of zero-point energy (ZPE) vibration on the absorption spectra of water clusters. Static ab initio calculations without ZPE showed that the first electronic transitions of (H(2)O)(n), (1)B(1)←(1)A(1), are blue-shifted as a function of cluster size (n): 7.38 eV (n = 1), 7.58 eV (n = 2) and 8.01 eV (n = 3). The inclusion of the ZPE vibration strongly affects the excitation energies of a water dimer, and a long red-tail appears in the range of 6.42-6.90 eV due to the structural flexibility of a water dimer. The ultraviolet photodissociation of water clusters and water ice surfaces is relevant to these results.
International Nuclear Information System (INIS)
Chen, Chung-De; Huang, Yen-Chieh; Chiang, Hsin-Lin; Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan; Chen, Chun-Jung
2014-01-01
A novel direct phase-selection method to select optimized phases from the ambiguous phases of a subset of reflections to replace the corresponding initial SAD phases has been developed. With the improved phases, the completeness of built residues of protein molecules is enhanced for efficient structure determination. Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (ϕ 1 and ϕ 2 ) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ DS list as a criterion to select optimized phases ϕ am from ϕ 1 or ϕ 2 of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases ϕ SAD has been developed. Based on this work, reflections with an angle θ DS in the range 35–145° are selected for an optimized improvement, where θ DS is the angle between the initial phase ϕ SAD and a preliminary density-modification (DM) phase ϕ DM NHL . The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination
Deluque Toro, C. E.; Mosquera Polo, A. S.; Gil Rebaza, A. V.; Landínez Téllez, D. A.; Roa-Rojas, J.
2018-04-01
We report first-principles calculations of the elastic properties, electronic structure and magnetic behavior performed over the Ba2NiMoO6 double perovskite. Calculations are carried out through the full-potential linear augmented plane-wave method within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient and Local Density Approximations, including spin polarization. The elastic properties calculated are bulk modulus (B), the elastic constants (C 11, C 12 and C 44), the Zener anisotropy factor (A), the isotropic shear modulus (G), the Young modulus (Y) and the Poisson ratio (υ). Structural parameters, total energies and cohesive properties of the perovskite are studied by means of minimization of internal parameters with the Murnaghan equation, where the structural parameters are in good agreement with experimental data. Furthermore, we have explored different antiferromagnetic configurations in order to describe the magnetic ground state of this compound. The pressure and temperature dependence of specific heat, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior C V ≈ C P was found at temperatures below T = 400 K, with Dulong-Petit limit values, which is higher than those, reported for simple perovskites.
Directory of Open Access Journals (Sweden)
Chelli S.
2015-12-01
Full Text Available The structural, elastic, electronic and thermodynamic properties of BaxSr1−xS ternary alloys have been investigated using the full-potential (linearized augmented plane wave method. The ground state properties, such as lattice constant, bulk modulus and elastic constants, are in good agreement with numerous experimental and theoretical data. The dependence of the lattice parameters, bulk modulus and band gap on the composition x was analyzed. Deviation of the lattice constant from Vegard’s law and the bulk modulus from linear concentration dependence (LCD was observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger et al. The thermodynamic stability of BaxSr1−xS alloy was investigated by calculating the excess enthalpy of mixing, ΔHm and the calculated phase diagram showed a broad miscibility gap with a critical temperature.
Chen, Chung-De; Huang, Yen-Chieh; Chiang, Hsin-Lin; Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan; Chen, Chun-Jung
2014-09-01
Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (φ1 and φ2) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ(DS) list as a criterion to select optimized phases φ(am) from φ1 or φ2 of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases φ(SAD) has been developed. Based on this work, reflections with an angle θ(DS) in the range 35-145° are selected for an optimized improvement, where θ(DS) is the angle between the initial phase φ(SAD) and a preliminary density-modification (DM) phase φ(DM)(NHL). The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.
Santos-Carballal, David; Ngoepe, Phuti E.; de Leeuw, Nora H.
2018-02-01
The spinel-structured lithium manganese oxide (LiMn2O4 ) is a material currently used as cathode for secondary lithium-ion batteries, but whose properties are not yet fully understood. Here, we report a computational investigation of the inversion thermodynamics and electronic behavior of LiMn2O4 derived from spin-polarized density functional theory calculations with a Hubbard Hamiltonian and long-range dispersion corrections (DFT+U-D3). Based on the analysis of the configurational free energy, we have elucidated a partially inverse equilibrium cation distribution for the LiMn2O4 spinel. This equilibrium degree of inversion is rationalized in terms of the crystal field stabilization effects and the difference between the size of the cations. We compare the atomic charges with the oxidation numbers for each degree of inversion. We found segregation of the Mn charge once these ions occupy the tetrahedral and octahedral sites of the spinel. We have obtained the atomic projections of the electronic band structure and density of states, showing that the normal LiMn2O4 has half-metallic properties, while the fully inverse spinel is an insulator. This material is in the ferrimagnetic state for the inverse and partially inverse cation arrangement. The optimized lattice and oxygen parameters, as well as the equilibrium degree of inversion, are in agreement with the available experimental data. The partial equilibrium degree of inversion is important in the interpretation of the lithium ion migration and surface properties of the LiMn2O4 spinel.
Energy Technology Data Exchange (ETDEWEB)
Miloud Abid, O.; Yakoubi, A. [Laboratoire d’Etudes des Matériaux et Instrumentations Expérimentales, Université Djilali Liabes de Sidi Bel-Abbes, 22000 (Algeria); Tadjer, A. [Modeling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, Sidi Bel-Abbes (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Azam, Sikander [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)
2014-12-15
Highlights: • The calculated structural parameters of RMn{sub 2}Ge{sub 2} (R = Ca, Nd and Y) compounds are found in good agreement with the experimental data. • The structural and band structure calculation reveals that these compounds are ferromagnetic brittle metals. • The elastic and thermodynamic properties for the herein studied compounds are investigated for the first time. - Abstract: Intermetallic RMn{sub 2}Ge{sub 2} ternary compounds have attracted considerable attention from researchers in recent years because they show strong indications for novel magnetic characteristics and they have the potential to reveal the mechanism of superlattices. The study of the paramagnetic, ferromagnetic and antiferromagnetic phases affirms the strong dependence to the distance between atomic species in these compounds. In this study, we investigated the structural, elastic, electronic and thermodynamic properties of the intermetallic RMn{sub 2}Ge{sub 2} (R = Ca, Nd and Y) compounds. To carry out this study, we used the full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo), a scheme of calculations developed within the frame work of density functional theory (DFT). To incorporate the exchange correlation (XC) energy and corresponding potential into the total energy calculations, local density approximation (LDA) parameterized by Perdew and Wang is taken into account. Analysis of the density of states (DOS) profile illustrates the conducting nature of these intermetallic compounds; with a predominantly contribution from the R and Mn-d states. At ambient conditions, calculations for elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 44}, C{sub 33} and C{sub 66}) are also performed, which point to their brittle character. In addition, the quasi harmonic Debye model was used to predict the thermal properties, together with relative expansion coefficients and heat capacity.
Vogt, Natalja; Abaev, Maxim A.; Rykov, Anatolii N.; Shishkov, Igor F.
2011-06-01
The molecular structure of succinic acid has been investigated by the gas-phase electron diffraction (GED) method for the first time. According to predictions of MP2/cc-pVTZ calculations, the molecule has 18 stable conformers with the C sbnd C sbnd C sbnd C chain in the gauche ( G) or anti ( A) configuration, and four of them, I ( G), II ( A), III ( G) and IV ( A) belonging to the C 2, C 2h, C 1 and C 1 point groups, respectively, with relative energies ΔE ZPE within 2.2 kcal/mol can be present at the experimental temperature of 445 K in noticeable amounts. The ratio of the conformers I:II:III:IV = 45(15):20(15):10(assumed):25(15) (in %) has been determined in the GED analysis guided by theoretical predictions. To take into account vibrational effects, the corrections Δ( r e - r a) to the experimental r a bond lengths were calculated from the MP2/cc-pVTZ quadratic and cubic force constants. The obtained equilibrium structural parameters of the dominant conformer I are the following (bond lengths in Å, angles in degrees): r e(C sp3sbnd C sp3) = 1.508(3), r e(C sp3sbnd C sp2) = 1.499(2), r e(C sbnd O) = 1.343(2), r e(C dbnd O) = 1.202(1), e(C sbnd C sbnd C) = 111.8(4), e(C sbnd C sbnd O) = 112.0(4), e(O sbnd C dbnd O) = 123.0(1), τ(C sbnd C sbnd C sbnd C) = 69.9(11). Yielding the best agreement with the GED structure, the MP2/cc-pVQZ approximation overestimates the C sbnd O and C dbnd O bond lengths by ca. 0.005(2) Å.
Zhao, Pengfei; Liang, Chongyun; Gong, Xiwen; Gao, Ran; Liu, Jiwei; Wang, Min; Che, Renchao
2013-08-01
Monodispersed manganese oxide (Mn1-xCox)3O4 (0 nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low temperature, ranging from 90 to 100 °C, without any inertia gas for protection. The influences of the Co dopant content on the critical reaction temperature required for the nanoparticle formation, electronic band structures, magnetic properties, and the microwave absorption capability of (Mn1-xCox)3O4 are comprehensively investigated by means of both experimental and theoretical approaches including powder X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), super conductivity quantum interference device (SQUID) examination, and first-principle simulations. Co is successfully doped into the Mn atomic sites of the (Mn1-xCox)3O4 lattice, which is further confirmed by EELS data acquired from one individual nanoparticle. Therefore, continuous solid solutions of well-crystallized (Mn1-xCox)3O4 products are achieved without any impurity phase or phase separation. With increases in the Co dopant concentration x from 0 to 0.5, the lattice parameters change systemically, where the overall saturation magnetization at 30 K increases due to the more intense coupling of the 3d electrons between Mn and Co, as revealed by simulations. The microwave absorption properties of the (Mn1-xCox)3O4 nanoparticles are examined between 2 and 18 GHz. The maximum absorption peak -11.0 dB of the x = 0 sample is enhanced to -11.5 dB for x = 0.2, -12.7 dB for x = 0.25, -15.6 dB for x = 0.33, and -24.0 dB for x = 0.5 respectively, suggesting the Co doping effects. Our results might provide novel insights into the understanding of the influences of metallic ion doping on the electromagnetic properties of metallic oxide nanomaterials.Monodispersed manganese oxide (Mn1-xCox)3O4 (0 nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low temperature, ranging from 90 to
Ab Initio Calculations for the BaTiO3 (001) Surface Structure
Institute of Scientific and Technical Information of China (English)
XUE Xu-Yan; WANG Chun-Lei; ZHONG Wei-Lie
2004-01-01
@@ The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field.We analyse their electronic structures (band structure, density of states and the electronic density redistribution with emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed.The band gap reduces especially for the TiO2 termination.
Energy Technology Data Exchange (ETDEWEB)
Feller, D.F.
1993-07-01
This collection of benchmark timings represents a snapshot of the hardware and software capabilities available for ab initio quantum chemical calculations at Pacific Northwest Laboratory`s Molecular Science Research Center in late 1992 and early 1993. The ``snapshot`` nature of these results should not be underestimated, because of the speed with which both hardware and software are changing. Even during the brief period of this study, we were presented with newer, faster versions of several of the codes. However, the deadline for completing this edition of the benchmarks precluded updating all the relevant entries in the tables. As will be discussed below, a similar situation occurred with the hardware. The timing data included in this report are subject to all the normal failures, omissions, and errors that accompany any human activity. In an attempt to mimic the manner in which calculations are typically performed, we have run the calculations with the maximum number of defaults provided by each program and a near minimum amount of memory. This approach may not produce the fastest performance that a particular code can deliver. It is not known to what extent improved timings could be obtained for each code by varying the run parameters. If sufficient interest exists, it might be possible to compile a second list of timing data corresponding to the fastest observed performance from each application, using an unrestricted set of input parameters. Improvements in I/O might have been possible by fine tuning the Unix kernel, but we resisted the temptation to make changes to the operating system. Due to the large number of possible variations in levels of operating system, compilers, speed of disks and memory, versions of applications, etc., readers of this report may not be able to exactly reproduce the times indicated. Copies of the output files from individual runs are available if questions arise about a particular set of timings.
Energy Technology Data Exchange (ETDEWEB)
Yu, Ching-Feng [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Cheng, Hsien-Chie, E-mail: hccheng@fcu.edu.tw [Department of Aerospace and Systems Engineering, Feng Chia University, Taichung 40724, Taiwan (China); Chen, Wen-Hwa, E-mail: whchen@pme.nthu.edu.tw [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
2016-05-01
First principles density functional theory calculations within the generalized gradient approximation are performed to comprehensively study the structural, elastic, electronic and thermodynamic properties of triclinic single and polycrystalline Cu{sub 7}In{sub 3}. The polycrystalline elastic properties are predicted using the Voigt–Reuss–Hill approximation and the thermodynamic properties are evaluated based on the quasi-harmonic Debye model. Their temperature, hydrostatic pressure or crystal orientation dependences are also addressed, and the predicted physical properties are compared with the literature experimental and theoretical data and also with those of three other Cu–In compounds, i.e., CuIn, Cu{sub 2}In and Cu{sub 11}In{sub 9}. The present calculations show that in addition to being a much better conductor compared to Cu{sub 2}In and Cu{sub 11}In{sub 9}, Cu{sub 7}In{sub 3} crystal reveals weak elastic anisotropy, high ductility and low stiffness, and tends to become more elastically isotropic at very high hydrostatic pressure. Moreover, the Cu{sub 7}In{sub 3} holds the largest high-temperature heat capacity among the four Cu–In compounds. - Highlights: • The physical property of Cu{sub 7}In{sub 3} is reported by first-principles calculations. • Pressure effect on the physical property of Cu{sub 7}In{sub 3} is presented. • The calculated lattice constants of Cu{sub 7}In{sub 3} agree well with the experimental data. • Cu{sub 7}In{sub 3} tends to become more elastically isotropic at very high pressure. • The heat capacity of Cu{sub 7}In{sub 3} is much larger than that of CuIn, Cu{sub 2}In and Cu{sub 11}In{sub 9}.
Mugnaioli, Enrico; Gemmi, Mauro; Merlini, Marco; Gregorkiewitz, Michele
2016-01-01
(Nax□1 − x)5[MnO2]13 has been synthesized with x = 0.80 (4), corresponding to Na0.31[MnO2]. This well known material is usually cited as Na0.4[MnO2] and is believed to have a romanèchite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (χ2 = 0.690, R wp = 0.051, R p = 0.037, R F2 = 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) Å, β = 105.0925 (16)°, V = 918.90 (4) Å3, Z = 2. A hitherto unknown [MnO2] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by egg-shaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)5[MnO2]13. The trivalent Mn3+ ions concentrate at two of the seven Mn sites where larger Mn—O distances and Jahn–Teller distortion are observed. One of the Mn3+ sites is five-coordinated in a square pyramid which, on oxidation to Mn4+, may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures. PMID:27910840
Zhao, Jing; Wang, Mei; Fu, Aiyun; Yang, Hongfang; Bu, Yuxiang
2015-08-03
We present an ab initio molecular dynamics (AIMD) simulation study into the transfer dynamics of an excess electron from its cavity-shaped hydrated electron state to a hydrated nucleobase (NB)-bound state. In contrast to the traditional view that electron localization at NBs (G/A/C/T), which is the first step for electron-induced DNA damage, is related only to dry or prehydrated electrons, and a fully hydrated electron no longer transfers to NBs, our AIMD simulations indicate that a fully hydrated electron can still transfer to NBs. We monitored the transfer dynamics of fully hydrated electrons towards hydrated NBs in aqueous solutions by using AIMD simulations and found that due to solution-structure fluctuation and attraction of NBs, a fully hydrated electron can transfer to a NB gradually over time. Concurrently, the hydrated electron cavity gradually reorganizes, distorts, and even breaks. The transfer could be completed in about 120-200 fs in four aqueous NB solutions, depending on the electron-binding ability of hydrated NBs and the structural fluctuation of the solution. The transferring electron resides in the π*-type lowest unoccupied molecular orbital of the NB, which leads to a hydrated NB anion. Clearly, the observed transfer of hydrated electrons can be attributed to the strong electron-binding ability of hydrated NBs over the hydrated electron cavity, which is the driving force, and the transfer dynamics is structure-fluctuation controlled. This work provides new insights into the evolution dynamics of hydrated electrons and provides some helpful information for understanding the DNA-damage mechanism in solution. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
International Nuclear Information System (INIS)
Garrett, W.R.
1979-01-01
Through the use of a molecular pseudopotential method, we determine the a approximate magnitudes of errors that result when electron affinity determinations of polar negative ions are made through ab initio calculations in which the use of a given basis set yields inappropriate values for permanent and induced dipole moments of the neutral molecule. These results should prove useful in assessing the adequacy of basis sets in ab initio calculations of molecular electron affinities for simple linear polar molecules
Electronic structure of shandite Co3Sn2S2
Dedkov, Y. S.; Holder, M.; Molodtsov, S. L.; Rosner, H.
2008-03-01
The electronic structure of shandite Co3Sn2S2 was determined by photoelectron spectroscopy and compared with ab initio band structure calculations. Presented results give evidence that this compound has half-metallic ferromagnetic properties.
Ab initio study of isomerism in molecular ions Li2AB+ with 10 valence electrons
International Nuclear Information System (INIS)
Charkin, O.P.; Mak-Ki, M.L.; Shlojer, P.R.
1997-01-01
Ab initio calculations of surfaces of Li 2 AB + molecular ion potential energy with biatomic anions AB - with 10 valence electrons have been made in the framework of approximations MP2/6-31G 1 /HF/6-31G*+ZPE(HF/6-31G*) and MP4SDTQ/631G*//MP2/6-31G*+ZPE(MP2/6-31G*). Influence of electron correlation on the accuracy of calculations of their structural and vibrational characteristics is studied. The following most favourable structures have been found: linear for Li 2 BO + , Li 2 CN + , and bent one for Li 2 BS + , with cations coordinated at different anion atoms; onium one for AlOLi 2 + , AlSLi 2 + , SiNLi 2 + and SiPLi 2 + with both cations at electronegative atom of anion
Ab initio nuclear structure - the large sparse matrix eigenvalue problem
Energy Technology Data Exchange (ETDEWEB)
Vary, James P; Maris, Pieter [Department of Physics, Iowa State University, Ames, IA, 50011 (United States); Ng, Esmond; Yang, Chao [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Sosonkina, Masha, E-mail: jvary@iastate.ed [Scalable Computing Laboratory, Ames Laboratory, Iowa State University, Ames, IA, 50011 (United States)
2009-07-01
The structure and reactions of light nuclei represent fundamental and formidable challenges for microscopic theory based on realistic strong interaction potentials. Several ab initio methods have now emerged that provide nearly exact solutions for some nuclear properties. The ab initio no core shell model (NCSM) and the no core full configuration (NCFC) method, frame this quantum many-particle problem as a large sparse matrix eigenvalue problem where one evaluates the Hamiltonian matrix in a basis space consisting of many-fermion Slater determinants and then solves for a set of the lowest eigenvalues and their associated eigenvectors. The resulting eigenvectors are employed to evaluate a set of experimental quantities to test the underlying potential. For fundamental problems of interest, the matrix dimension often exceeds 10{sup 10} and the number of nonzero matrix elements may saturate available storage on present-day leadership class facilities. We survey recent results and advances in solving this large sparse matrix eigenvalue problem. We also outline the challenges that lie ahead for achieving further breakthroughs in fundamental nuclear theory using these ab initio approaches.
Ab initio nuclear structure - the large sparse matrix eigenvalue problem
International Nuclear Information System (INIS)
Vary, James P; Maris, Pieter; Ng, Esmond; Yang, Chao; Sosonkina, Masha
2009-01-01
The structure and reactions of light nuclei represent fundamental and formidable challenges for microscopic theory based on realistic strong interaction potentials. Several ab initio methods have now emerged that provide nearly exact solutions for some nuclear properties. The ab initio no core shell model (NCSM) and the no core full configuration (NCFC) method, frame this quantum many-particle problem as a large sparse matrix eigenvalue problem where one evaluates the Hamiltonian matrix in a basis space consisting of many-fermion Slater determinants and then solves for a set of the lowest eigenvalues and their associated eigenvectors. The resulting eigenvectors are employed to evaluate a set of experimental quantities to test the underlying potential. For fundamental problems of interest, the matrix dimension often exceeds 10 10 and the number of nonzero matrix elements may saturate available storage on present-day leadership class facilities. We survey recent results and advances in solving this large sparse matrix eigenvalue problem. We also outline the challenges that lie ahead for achieving further breakthroughs in fundamental nuclear theory using these ab initio approaches.
International Nuclear Information System (INIS)
Smardon, R.D.; Srivastava, G.P.
2004-01-01
Using a first principles pseudopotential method we have studied the adsorption of H on the high index Si(1 1 4)-(2x1) surface within the local density approximation. This stable surface is found to be both chemically and electronically passivated by two different coverages of hydrogen: 1.0 ML and 1.5 ML. For the 1.0 ML coverage all the A- and B-type dimer bond lengths have equalised to 2.40 Angst and the rebonded lengths are slightly longer at 2.48 Angst. Hydrogen passivation, for both coverages, leads the surface bands of the clean Si(1 1 4)-(2x1) surface to move into the bulk valence and conduction bands. Differences in the density of states for the clean, 1.0 ML and 1.5 ML coverages were observed and are discussed
Vlahos, Vasilios; Booske, John H.; Morgan, Dane
2010-02-01
Microwave, x-ray, and radio-frequency radiation sources require a cathode emitting electrons into vacuum. Thermionic B-type dispenser cathodes consist of BaxOz coatings on tungsten (W), where the surface coatings lower the W work function and enhance electron emission. The new and promising class of scandate cathodes modifies the B-type surface through inclusion of Sc, and their superior emissive properties are also believed to stem from the formation of a low work function surface alloy. In order to better understand these cathode systems, density-functional theory (DFT)-based ab initio modeling is used to explore the stability and work function of BaxScyOz on W(001) monolayer-type surface structures. It is demonstrated how surface depolarization effects can be calculated easily using ab initio calculations and fitted to an analytic depolarization equation. This approach enables the rapid extraction of the complete depolarization curve (work function versus coverage relation) from relatively few DFT calculations, useful for understanding and characterizing the emitting properties of novel cathode materials. It is generally believed that the B-type cathode has some concentration of Ba-O dimers on the W surface, although their structure is not known. Calculations suggest that tilted Ba-O dimers are the stable dimer surface configuration and can explain the observed work function reduction corresponding to various dimer coverages. Tilted Ba-O dimers represent a new surface coating structure not previously proposed for the activated B-type cathode. The thermodynamically stable phase of Ba and O on the W surface was identified to be the Ba0.25O configuration, possessing a significantly lower Φ value than any of the Ba-O dimer configurations investigated. The identification of a more stable Ba0.25O phase implies that if Ba-O dimers cover the surface of emitting B-type cathodes, then a nonequilibrium steady state must dominate the emitting surface. The identification of
Ab initio study on electron excitation and electron transfer in tryptophan-tyrosine system
International Nuclear Information System (INIS)
Tong Jing; Li Xiangyuan
2002-01-01
In this article, ab initio calculation has been performed to evaluate the transition energy of electronic excitation in tryptophan and tyrosine by using semiempirical molecular orbital method AM1 and complete active space self-consistent field method. The solvent effect has been considered by means of the conductor-like screening model. After geometric optimizations of isolated tryptophan and tyrosine, and their corresponding radicals and cations, reaction heat of these electron transfer reactions have been obtained by the means of complete active space self-consistent field method. The transition energies from the ground state, respectively, to the lowest excited state and to the lowest triplet state of these two amino acids are also calculated and compared with the experimentally observed values. The ionization potential and electron affinity are also calculated for tryptophan and tyrosine employing Koopmans' theorem and ab initio calculation. Compared with the experimental measurements, the theoretical results are found satisfactory. Theoretical results give good explanations on the experimental phenomena that N 3 · can preferably oxide the side chain of tryptophan residue and then the electron transfer from tyrosine residue to tryptophan residue follows in peptides involving tryptophan and tyrosine
Ab initio electronic properties of dual phosphorus monolayers in silicon
DEFF Research Database (Denmark)
Drumm, Daniel W.; Per, Manolo C.; Budi, Akin
2014-01-01
In the midst of the epitaxial circuitry revolution in silicon technology, we look ahead to the next paradigm shift: effective use of the third dimension - in particular, its combination with epitaxial technology. We perform ab initio calculations of atomically thin epitaxial bilayers in silicon...
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.
An Efficient Method for Electron-Atom Scattering Using Ab-initio Calculations
Energy Technology Data Exchange (ETDEWEB)
Xu, Yuan; Yang, Yonggang; Xiao, Liantuan; Jia, Suotang [Shanxi University, Taiyuan (China)
2017-02-15
We present an efficient method based on ab-initio calculations to investigate electron-atom scatterings. Those calculations profit from methods implemented in standard quantum chemistry programs. The new approach is applied to electron-helium scattering. The results are compared with experimental and other theoretical references to demonstrate the efficiency of our method.
International Nuclear Information System (INIS)
Thompson, K.; Martinez, T.J.
1999-01-01
We present a new approach to first-principles molecular dynamics that combines a general and flexible interpolation method with ab initio evaluation of the potential energy surface. This hybrid approach extends significantly the domain of applicability of ab initio molecular dynamics. Use of interpolation significantly reduces the computational effort associated with the dynamics over most of the time scale of interest, while regions where potential energy surfaces are difficult to interpolate, for example near conical intersections, are treated by direct solution of the electronic Schroedinger equation during the dynamics. We demonstrate the concept through application to the nonadiabatic dynamics of collisional electronic quenching of Li(2p). Full configuration interaction is used to describe the wave functions of the ground and excited electronic states. The hybrid approach agrees well with full ab initio multiple spawning dynamics, while being more than an order of magnitude faster. copyright 1999 American Institute of Physics
A hydronitrogen solid: high pressure ab initio evolutionary structure searches
International Nuclear Information System (INIS)
Hu Anguang; Zhang Fan
2011-01-01
High pressure ab initio evolutionary structure searches resulted in a hydronitrogen solid with a composition of (NH) 4 . The structure searches also provided two molecular isomers, ammonium azide (AA) and trans-tetrazene (TTZ) which were previously discovered experimentally and can be taken as molecular precursors for high pressure synthesis of the hydronitrogen solid. The computed pressure versus enthalpy diagram showed that the transformation pressure to the hydronitrogen solid is 36 GPa from AA and 75 GPa from TTZ. Its metastability was analyzed by the phonon dispersion spectrum and room-temperature vibrational density of state together with the transformation energy barrier back to molecular phases at 298 K. The predicted energy barrier of 0.21 eV/atom means that the proposed hydronitrogen solid should be very stable at ambient conditions. (fast track communication)
Indian Academy of Sciences (India)
Abstract. Results of ab initio electronic structure calculations on the compound MgB2 using the. FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, c/a ratio and the bulk modulus, all of which are in excellent ...
Indian Academy of Sciences (India)
Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with ...
Ab initio calculation of the electronic absorption spectrum of liquid water
International Nuclear Information System (INIS)
Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa
2014-01-01
The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase
Ab-initio study on electronic properties of rocksalt SnAs
Babariya, Bindiya; Vaghela, M. V.; Gajjar, P. N.
2018-05-01
Within the frame work of Local Density Approximation of Exchange and Correlation, ab-initio method of density functional theory with Abinit code is used to compute electronic energy band structure, density of States and charge density of SnAs in rocksalt phase. Our result after optimization for lattice constant agrees with experimental value within 0.59% deviation. The computed electronic energy bands in high symmetry directions Γ→K→X→Γ→L→X→W→L→U shown metallic nature. The lowest band in the electronic band structure is showing band-gap approximately 1.70 eV from next higher band and no crossing between lowest two bands are seen. The density of states revels p-p orbit hybridization between Sn and As atoms. The spherical contour around Sn and As in the charge density plot represent partly ionic and partly covalent bonding. Fermi surface topology is the resultant effect of the single band crossing along L direction at Ef.
Tunneling of electrons via rotor–stator molecular interfaces: Combined ab initio and model study
Energy Technology Data Exchange (ETDEWEB)
Petreska, Irina, E-mail: irina.petreska@pmf.ukim.mk [Institute of Physics, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, PO Box 162, 1000 Skopje, Former Yugolav Republic of Macedonia, The (Macedonia, The Former Yugoslav Republic of); Ohanesjan, Vladimir [Institute of Physics, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, PO Box 162, 1000 Skopje, Former Yugolav Republic of Macedonia, The (Macedonia, The Former Yugoslav Republic of); Pejov, Ljupčo [Institute of Chemistry, Department of Physical Chemistry, Ss. Cyril and Methodius University, Arhimedova 5, P.O. Box 162, 1000 Skopje, Former Yugolav Republic of Macedonia, The (Macedonia, The Former Yugoslav Republic of); Kocarev, Ljupčo [Macedonian Academy of Sciences and Arts, Krste Misirkov 2, PO Box 428, 1000 Skopje, Former Yugolav Republic of Macedonia, The (Macedonia, The Former Yugoslav Republic of); Faculty of Computer Science and Engineering, Ss. Cyril and Methodius University, Skopje, Former Yugolav Republic of Macedonia, The (Macedonia, The Former Yugoslav Republic of)
2016-07-01
Tunneling of electrons through rotor–stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons’ formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green’s Function Formalism.
Direct observations of the MOF (UiO-66) structure by transmission electron microscopy
Zhu, Liangkui; Zhang, Daliang; Xue, Ming; Li, Huan; Qiu, Shilun
2013-01-01
As a demonstration of ab initio structure characterizations of nano metal organic framework (MOF) crystals by high resolution transmission electron microscopy (HRTEM) and electron diffraction tomography methods, a Zr-MOF (UiO-66) structure
Energy Technology Data Exchange (ETDEWEB)
Osmani, O; Duvenbeck, A; Akcoeltekin, E; Meyer, R; Schleberger, M [Department of Physics, University of Duisburg-Essen, D-47048 Duisburg (Germany); Lebius, H [CIMAP, blvd Henri Becquerel, 14070 Caen (France)], E-mail: marika.schleberger@uni-due.de
2008-08-06
In recent experiments the irradiation of insulators of perovskite type with swift (E{approx}100 MeV) heavy ions under glancing incidence has been shown to provide a unique means to generate periodically arranged nanodots at the surface. The physical origin of these patterns has been suggested as stemming from a highly anisotropic electron density distribution within the bulk. In order to show the relevance of the electron density distribution of the target we present a model calculation for the system Xe{sup 23+} {yields} SrTiO{sub 3} that is known to produce the aforementioned surface modifications. On the basis of the Lindhard model of electronic stopping, we employ highly-resolved ab initio electron density data to describe the conversion of kinetic energy into excitation energy along the ion track. The primary particle dynamics are obtained via integration of the Newtonian equations of motion that are governed by a space- and time-dependent frictional force originating from Lindhard stopping. The analysis of the local electronic stopping power along the ion track reveals a pronounced periodic structure. The periodicity length varies strongly with the particular choice of the polar angle of incidence and is directly correlated to the experimentally observed formation of periodic nanodots at insulator surfaces.
Ab initio simulations and neutron scattering studies of structure and dynamics in PdH
International Nuclear Information System (INIS)
Totolici, I.E.
2001-07-01
The work presented in this PhD thesis is concerned with the interpretation of the neutron scattering measurements from the palladium hydrogen system by means of ab initio electronic structure calculations. The motivation of performing such calculations was due to recent neutron scattering studies on this system that showed a strong directional dependence to the dynamical structure factor together with a complex dependence on energy. Here we attempt to describe the origin of these features by ab initio simulations of the dynamical structure factor. The method assumes an adiabatic separation of the motion of the proton and palladium atoms. The proton wave functions are calculated by a direct solution of the associated single-particle Schroedinger equation using a plane wave basis set method and a mapping of the adiabatic surface. The Fourier components of the adiabatic potential are obtained from LDA pseudopotential calculations. Using Fermi's golden rule within the Born approximation we were then able to calculate the dynamical structure factor, S(Q,ω), for exciting the proton from its ground state to various excited states as a function of the magnitude and direction of the scattering wave vector. The results are in agreement with the inelastic neutron scattering spectra and allow us to identify the origin of previous inexplicable features, in particular the strong directional dependence to the experimental data. The method was extended to investigate the expansion of the equilibrium lattice constant as a function of the H isotope when the zero-point energy of the proton/deuterium is explicitly taken into account in the relaxation process. The results we obtained predicted a bigger lattice constant for the hydride, as expected. Furthermore, other complex ab initio calculations were carried out in order to describe the origin of the large optic dispersion, seen previously in the coherent neutron scattering data. Our calculated dispersion proved to be in good
Summation of Parquet diagrams as an ab initio method in nuclear structure calculations
International Nuclear Information System (INIS)
Bergli, Elise; Hjorth-Jensen, Morten
2011-01-01
Research highlights: → We present a Green's function based approach for doing ab initio nuclear structure calculations. → In particular the sum the subset of so-called Parquet diagrams. → Applying the theory to a simple but realistic model, results in good agreement with other ab initio methods. → This opens up for ab initio calculations for medium-heavy nuclei. - Abstract: In this work we discuss the summation of the Parquet class of diagrams within Green's function theory as a possible framework for ab initio nuclear structure calculations. The theory is presented and some numerical details are discussed, in particular the approximations employed. We apply the Parquet method to a simple model, and compare our results with those from an exact solution. The main conclusion is that even at the level of approximation presented here, the results shows good agreement with other comparable ab initio approaches.
Thermal, spectroscopic, and ab initio structural characterization of carprofen polymorphs.
Bruni, Giovanna; Gozzo, Fabia; Capsoni, Doretta; Bini, Marcella; Macchi, Piero; Simoncic, Petra; Berbenni, Vittorio; Milanese, Chiara; Girella, Alessandro; Ferrari, Stefania; Marini, Amedeo
2011-06-01
Commercial and recrystallized polycrystalline samples of carprofen, a nonsteroidal anti-inflammatory drug, were studied by thermal, spectroscopic, and structural techniques. Our investigations demonstrated that recrystallized sample, stable at room temperature (RT), is a single polymorphic form of carprofen (polymorph I) that undergoes an isostructural polymorphic transformation by heating (polymorph II). Polymorph II remains then metastable at ambient conditions. Commercial sample is instead a mixture of polymorphs I and II. The thermodynamic relationships between the two polymorphs were determined through the construction of an energy/temperature diagram. The ab initio structural determination performed on synchrotron X-Ray powder diffraction patterns recorded at RT on both polymorphs allowed us to elucidate, for the first time, their crystal structure. Both crystallize in the monoclinic space group type P2(1) /c, and the unit cell similarity index and the volumetric isostructurality index indicate that the temperature-induced polymorphic transformation I → II is isostructural. Polymorphs I and II are conformational polymorphs, sharing a very similar hydrogen bond network, but with different conformation of the propanoic skeleton, which produces two different packing. The small conformational change agrees with the low value of transition enthalpy obtained by differential scanning calorimetry measurements and the small internal energy computed with density functional methods. Copyright © 2011 Wiley-Liss, Inc.
International Nuclear Information System (INIS)
Manson, S.T.; Miller, J.H.; Pacific Northwest Lab., Richland, WA)
1983-01-01
Ionization cross sections for heavy ions and electrons incident on various atoms and molecules are required in the modeling of the interaction of radiation with matter. For each case, the energy distribution of secondary electrons (the single differential cross section, SDCS) is needed over a broad range of projectile and secondary electron (delta-ray) energies. In many cases the energy and angular distribution of secondary electrons (the double differential cross section, DDCS) is also necessary. Clearly, it would be desirable to have laboratory SDCS and DDCS measurements for all of the cases required. For a variety of reasons, this is not yet possible. Thus, one must turn elsewhere to obtain the needed cross sections. In this paper, we discuss cross sections obtained in two different ways; ab initio theory based on the first Born approximation, and a semi-empirical method based on the Bethe-Born Approximation. In both cases, results on helium will be presented since the largest amount of data is available in this case. Applications of both methods to other target species are given in the references. The accuracy of the methods and plans for the near future are also discussed. 23 references, 6 figures
Institute of Scientific and Technical Information of China (English)
YAO Wen-Zhi; YAO Jian-Bin; LI Si-Dian
2012-01-01
A systematic density functional theory and wave function theory investigation on the geometrical and electronic properties of A1Aun0/" (n = 2-4) clusters has been performed in this work. A1Aun- anions prove to possess ground states of the V-shaped C2v A1Au2, umbrella-shaped C3v A1Au3, and perfect tetrahedral Td A1Au4", while their neutrals favor the V-shaped CEv A1Au2, perfect planar triangular D3h A1Au3, and severely distorted Cs A1Au4, respectively. Aluminum aurides appear to be analogous to the corresponding aluminum hydrides, expect C~ A1Au4. Molecular orbitals (MOs) analyses also support this conclusion. Detailed orbital analyses indicate that Au 6s makes 94-96% and Au 5d makes 6-4% contribution to the Au-based orbitals in A1-Au bonds, which is smaller than the BAun0/- series, partially reflecting the relativistic effect of gold. The one-electron detachment energies of the anions and characteristic stretching vibrational frequencies of A1-Au bonds between 100-400 cm-1 have been calculated to facilitate future experimental characterization of these clusters.
Ab Initio Predictions of Structures and Densities of Energetic Solids
National Research Council Canada - National Science Library
Rice, Betsy M; Sorescu, Dan C
2004-01-01
We have applied a powerful simulation methodology known as ab initio crystal prediction to assess the ability of a generalized model of CHNO intermolecular interactions to predict accurately crystal...
Electronic structure and tautomerism of aryl ketones
International Nuclear Information System (INIS)
Novak, Igor; Klasinc, Leo; Šket, Boris; McGlynn, S.P.
2015-01-01
Graphical abstract: Photoelectron spectroscopy, tautomerism. - Highlights: • UV photoelectron spectroscopy of aryl ketones. • The relative stability of tautomers and their electronic structures. • The factors influencing tautomerism. - Abstract: The electronic structures of several aryl ketones (AK) and their α-halo derivatives have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of the AK derivatives are discussed
Electronic structure and tautomerism of aryl ketones
Energy Technology Data Exchange (ETDEWEB)
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); Šket, Boris, E-mail: Boris.Sket@fkkt.uni-lj.si [Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 (Slovenia); McGlynn, S.P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2015-07-15
Graphical abstract: Photoelectron spectroscopy, tautomerism. - Highlights: • UV photoelectron spectroscopy of aryl ketones. • The relative stability of tautomers and their electronic structures. • The factors influencing tautomerism. - Abstract: The electronic structures of several aryl ketones (AK) and their α-halo derivatives have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of the AK derivatives are discussed.
Many-body perturbation theory for ab initio nuclear structure
International Nuclear Information System (INIS)
Tichai, Alexander
2017-01-01
The solution of the quantum many-body problem for medium-mass nuclei using realistic nuclear interactions poses a superbe challenge for nuclear structure research. Because an exact solution can only be provided for the lightest nuclei, one has to rely on approximate solutions when proceeding to heavier systems. Over the past years, tremendous progress has been made in the development and application of systematically improvable expansion methods and an accurate description of nuclear observables has become viable up to mass number A ∼ 100. While closed-shell systems are consistently described via a plethora of different many-body methods, the extension to genuine open-shell systems still remains a major challenge and up to now there is no ab initio many-body method which applies equally well to systems with even and odd mass numbers. The goal of this thesis is the development and implementation of innovative perturbative approaches with genuine open-shell capabilities. This requires the extension of well-known single-reference approaches to more general vacua. In this work we choose two complementary routes for the usage of generalized reference states. First, we derive a new ab initio approach based on multi-configurational reference states that are conveniently derived from a prior no-core shell model calculation. Perturbative corrections are derived via second-order many-body perturbation theory, thus, merging configuration interaction and many-body perturbation theory. The generality of this ansatz enables for a treatment of medium-mass systems with arbitrary mass number, as well as the extension to low-lying excited states such that ground and excited states are treated on an equal footing. In a complementary approach, we use reference states that break a symmetry of the underlying Hamiltonian. In the simplest case this corresponds to the expansion around a particle-number-broken Hartree-Fock-Bogolyubov vacuum which is obtained from a mean-field calculation
International Nuclear Information System (INIS)
Rubin, Yu.V.; Belous, L.F.
2012-01-01
Self-associates of nucleic acid components (stacking trimers and tetramers of the base pairs of nucleic acids) and short fragments of nucleic acids are nanoparticles (linear sizes of these particles are more than 10 A). Modern quantum-mechanical methods and softwares allow one to perform ab initio calculations of the systems consisting of 150-200 atoms with enough large basis sets (for example, 6-31G * ). The aim of this work is to reveal the peculiarities of molecular and electronic structures, as well as the energy features of nanoparticles of nucleic acid components. We had carried out ab initio calculations of the molecular structure and interactions in the stacking dimer, trimer, and tetramer of nucleic base pairs and in the stacking (TpG)(ApC) dimer and (TpGpC) (ApCpG) trimer of nucleotides, which are small DNA fragments. The performed calculations of molecular structures of dimers and trimers of nucleotide pairs showed that the interplanar distance in the structures studied is equal to 3.2 A on average, and the helical angle in a trimer is approximately equal to 30 o : The distance between phosphor atoms in neighboring chains is 13.1 A. For dimers and trimers under study, we calculated the horizontal interaction energies. The analysis of interplanar distances and angles between nucleic bases and their pairs in the calculated short oligomers of nucleic acid base pairs (stacking dimer, trimer, and tetramer) has been carried out. Studies of interactions in the calculated short oligomers showed a considerable role of the cross interaction in the stabilization of the structures. The contribution of cross interactions to the horizontal interactions grows with the length of an oligomer. Nanoparticle components get electric charges in nanoparticles. Longwave low-intensity bands can appear in the electron spectra of nanoparticles.
Ab initio random structure search for 13-atom clusters of fcc elements
International Nuclear Information System (INIS)
Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M
2013-01-01
The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd 13 and Au 13 , we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au 13 , which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons. (paper)
Moradian, Rostam; Behzad, Somayeh; Azadi, Sam
2008-09-01
By using ab initio density functional theory we investigated the structural and electronic properties of semiconducting (7, 0), (8, 0) and (10, 0) carbon nanotube bundles. The energetic and electronic evolutions of nanotubes in the bundling process are also studied. The effects of inter-tube coupling on the electronic dispersions of semiconducting carbon nanotube bundles are demonstrated. Our results show that the inter-tube coupling decreases the energy gap in semiconducting nanotubes. We found that bundles of (7, 0) and (8, 0) carbon nanotubes have metallic feature, while (10, 0) bundle is a semiconductor with an energy gap of 0.22 eV. To clarify our results the band structures of isolated and bundled nanotubes are compared.
Importance of dispersion and electron correlation in ab initio protein folding.
He, Xiao; Fusti-Molnar, Laszlo; Cui, Guanglei; Merz, Kenneth M
2009-04-16
Dispersion is well-known to be important in biological systems, but the effect of electron correlation in such systems remains unclear. In order to assess the relationship between the structure of a protein and its electron correlation energy, we employed both full system Hartree-Fock (HF) and second-order Møller-Plesset perturbation (MP2) calculations in conjunction with the Polarizable Continuum Model (PCM) on the native structures of two proteins and their corresponding computer-generated decoy sets. Because of the expense of the MP2 calculation, we have utilized the fragment molecular orbital method (FMO) in this study. We show that the sum of the Hartree-Fock (HF) energy and force field (LJ6)-derived dispersion energy (HF + LJ6) is well correlated with the energies obtained using second-order Møller-Plesset perturbation (MP2) theory. In one of the two examples studied, the correlation energy as well as the empirical dispersive energy term was able to discriminate between native and decoy structures. On the other hand, for the second protein we studied, neither the correlation energy nor dispersion energy showed discrimination capabilities; however, the ab initio MP2 energy and the HF+LJ6 both ranked the native structure correctly. Furthermore, when we randomly scrambled the Lennard-Jones parameters, the correlation between the MP2 energy and the sum of the HF energy and dispersive energy (HF+LJ6) significantly drops, which indicates that the choice of Lennard-Jones parameters is important.
All-electron ab initio investigation of the electronic states of the PdC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
2001-01-01
The electronic structure of transition metal containing molecules are extremely complicated and extensive calculations are required for reliable descriptions. In spite of this the results can often be interpreted in simple terms. The electronic structure of PdC is consistent with the molecular or...
Electronic structure and tautomerism of thioamides
Energy Technology Data Exchange (ETDEWEB)
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); McGlynn, Sean P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2016-05-15
Highlights: • Electronic structure of thioamide group and its relation to Lewis basicity. • Tautomerism of the (thio)amide groups. • Substituent effects on the electronic structure of (thio)amide group. - Abstract: The electronic structures of several thioamides have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of thioamide derivatives are discussed. The predominant tautomers in the gas phase are of keto–(thio)keto form. The addition of cyclohexanone moiety to the thioamide group enhances the Lewis base character of the sulfur atom. The addition of phenyl group to the (thio)amide group significantly affects its electronic structure.
Ab-initio Computation of the Electronic, transport, and Bulk Properties of Calcium Oxide.
Mbolle, Augustine; Banjara, Dipendra; Malozovsky, Yuriy; Franklin, Lashounda; Bagayoko, Diola
We report results from ab-initio, self-consistent, local Density approximation (LDA) calculations of electronic and related properties of calcium oxide (CaO) in the rock salt structure. We employed the Ceperley and Alder LDA potential and the linear combination of atomic orbitals (LCAO) formalism. Our calculations are non-relativistic. We implemented the LCAO formalism following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). The BZW-EF method involves a methodical search for the optimal basis set that yields the absolute minima of the occupied energies, as required by density functional theory (DFT). Our calculated, indirect band gap of 6.91eV, from towards the L point, is in excellent agreement with experimental value of 6.93-7.7eV, at room temperature (RT). We have also calculated the total (DOS) and partial (pDOS) densities of states as well as the bulk modulus. Our calculated bulk modulus is in excellent agreement with experiment. Work funded in part by the US Department of Energy (DOE), National Nuclear Security Administration (NNSA) (Award No.DE-NA0002630), the National Science Foundation (NSF) (Award No, 1503226), LaSPACE, and LONI-SUBR.
Ab initio calculation of electron excitation energies in solids
International Nuclear Information System (INIS)
Louie, S.G.
1996-02-01
Progress in the first-principles calculation of electron excitation energies in solids is discussed. Quasiparticle energies are computed by expanding the electron self energy to first order in the screened Coulomb interaction in the so-called GW approximation. The method was applied to explain and predict spectroscopic properties of a variety of systems. Several illustrative applications to semiconductors, materials under pressure, chemisorption, and point defects in solids are presented. A recent reformulation of the method employing mixed- space functions and imaginary time techniques is also discussed
All-electron ab initio calculations of YBa2Cu3O7 with self-consistence crystal field
Institute of Scientific and Technical Information of China (English)
刘洪霖; 陈念贻
1995-01-01
The quantum chemical calculations of cluster YBa2Cu3O7 considering all electrons have been per-formed by using the ab initio HF method with self-consistence crystal field.A Hartree-Fork surface potentialis proposed to make an asymmetric duster model possess a relatively symmetric potential field and to obtaina relatively symmetric electronic structure,electronic distributions,frontier orbitals,and bond order,etc.Thesuggestions that there exists a covalent bonding complex,[CuO2-O-CuO-O-Cu2]6,8-,in the cell unit ofthe crystal,and the cell units are connected with each other by ionic bonds along the c direction of the crys-tal lattice are offered based on the chemical bonding characteristics from the calculated results.The importantcontribution of the apical oxygen to superconductivities is emphasized as well.
Ab initio calculations of the structure and conformations of 2,6-lutidine
International Nuclear Information System (INIS)
Porcinai, S.; Foggi, P.
1997-01-01
Ab initio molecular orbital calculations at the SCF level have been utilized to determine the structure and the electronic and vibrational properties of 2,6-lutidine (2,6-dimethyl-pyridine) in the ground electronic state. Comparative calculations have been performed on the parent molecule pyridine. Structure predictions of both molecules are in good agreement with experimental data. The most stable rotamer of 2,6-lutidine has C 2v symmetry with one of the C-H bonds of both the methyl groups lying in the plane of the aromatic ring and pointing in the opposite direction with respect to the nitrogen atom. This is the result of the minimization of competing forces deriving from steric hindrance and electronic stabilization. Vibrational frequencies and oscillator strengths of C-H stretching in the fundamental region have been calculated for both pyridine and the most stable rotamer of 2,6-lutidine and compared to IR data obtained in pure liquids. The potential energy profile of the C-H bond in and out of plane has been investigated up to five times the equilibrium distance. The trend of the potential curves confirms that the C-H bond lying in the plane has a higher dissociation energy than that of the in-plane bonds as observed in experiments on vibrational overtones
Xu, Dong; Zhang, Yang
2012-07-01
Ab initio protein folding is one of the major unsolved problems in computational biology owing to the difficulties in force field design and conformational search. We developed a novel program, QUARK, for template-free protein structure prediction. Query sequences are first broken into fragments of 1-20 residues where multiple fragment structures are retrieved at each position from unrelated experimental structures. Full-length structure models are then assembled from fragments using replica-exchange Monte Carlo simulations, which are guided by a composite knowledge-based force field. A number of novel energy terms and Monte Carlo movements are introduced and the particular contributions to enhancing the efficiency of both force field and search engine are analyzed in detail. QUARK prediction procedure is depicted and tested on the structure modeling of 145 nonhomologous proteins. Although no global templates are used and all fragments from experimental structures with template modeling score >0.5 are excluded, QUARK can successfully construct 3D models of correct folds in one-third cases of short proteins up to 100 residues. In the ninth community-wide Critical Assessment of protein Structure Prediction experiment, QUARK server outperformed the second and third best servers by 18 and 47% based on the cumulative Z-score of global distance test-total scores in the FM category. Although ab initio protein folding remains a significant challenge, these data demonstrate new progress toward the solution of the most important problem in the field. Copyright © 2012 Wiley Periodicals, Inc.
Ab initio study of low-energy electron collisions with ethylene
International Nuclear Information System (INIS)
Trevisan, C.S.; Orel, A.E.; Rescigno, T.N.
2003-01-01
We present the results of an investigation of elastic electron scattering by ethylene C 2 H 4 with incident electron energies ranging from 0.5 to 20 eV, using the complex Kohn variational method. These fully ab initio calculations accurately reproduce experimental angular differential cross sections at energies below 3 eV. Low-energy electron scattering by ethylene is sensitive to the inclusion of electronic correlation and target-distortion effects. We therefore report results that describe the dynamic polarization of the target by the incident electron and involve calculations over a range of different geometries, including the effects of nuclear motion in the resonant 2 B 2g symmetry with an adiabatic nuclei treatment of the C-C stretch mode. The inclusion of dynamic polarization and the effect of nuclear motion are equally critical in obtaining accurate results. The calculated cross sections are compared with recent experimental measurements
Ab initio determination of effective electron-phonon coupling factor in copper
Ji, Pengfei; Zhang, Yuwen
2016-04-01
The electron temperature Te dependent electron density of states g (ε), Fermi-Dirac distribution f (ε), and electron-phonon spectral function α2 F (Ω) are computed as prerequisites before achieving effective electron-phonon coupling factor Ge-ph. The obtained Ge-ph is implemented into a molecular dynamics (MD) and two-temperature model (TTM) coupled simulation of femtosecond laser heating. By monitoring temperature evolutions of electron and lattice subsystems, the result utilizing Ge-ph from ab initio calculation shows a faster decrease of Te and increase of Tl than those using Ge-ph from phenomenological treatment. The approach of calculating Ge-ph and its implementation into MD-TTM simulation is applicable to other metals.
Odell, Anders
2011-10-03
The influence of the electrode\\'s Fermi surface on the transport properties of a photoswitching molecule is investigated with state-of-the-art ab initio transport methods. We report results for the conducting properties of the two forms of dithienylethene attached either to Ag or to nonmagnetic Ni leads. The I-V curves of the Ag/dithienylethene/Ag device are found to be very similar to those reported previously for Au. In contrast, when Ni is used as the electrode material the zero-bias transmission coefficient is profoundly different as a result of the role played by the Ni d bands in the bonding between the molecule and the electrodes. Intriguingly, despite these differences the overall conducting properties depend little on the electrode material. We thus conclude that electron transport in dithienylethene is, for the cases studied, mainly governed by the intrinsic electronic structure of the molecule. © 2011 American Physical Society.
Chan, Ka Wai
The solvation and electronic structures of M+Ln, with M+ = Mg+ and Cat, L = H2O, CH 3OH and NH3, n=1-6 were investigated by ab initio calculations using G03 package and density functional theory based ab initio molecular dynamics (AIMD) simulations with projector augmented-wave (PAW) method and a planewave basis set using Vienna Ab initio Simulation Package (VASP). Furthermore, ab initio studies on the intracluster reactions of Mg+ and Ca+ ions with different solvent molecules, H2O, CH3OH and NH3, were also done using G03 package. Finally, the elimination of a H atom in Na(H2O)n was studied. Such studies on the interactions and reactivity in gas clusters can provide insights into their analogies existing in condense phase. Interactions of Mg+ and Ca+ ions in different solvent molecules, H2O, CH3OH and NH3, were calculated with B3LYP and MP2 methods with basis sets 6-31+g** and 6-311+g**. A systematic comparison on the structures and reactivities of these clusters should provide a better understanding on the interplay of the ion-solvent, solvent-solvent, and electron-solvent interactions. It can provide a better understanding on the structures and bonding of complexes having analogies to those existing in condense phase. For Mg+(CH3OH)n and Ca+(CH 3OH)n, both H-elimination from OH/CH bond and CH3-elimination were investigated. H-elimination from O---H bond becomes more accessible for large cluster due to the diffusion of electron density to O---H bond. Studies on the H-elimination in Mg+(NH3)n and H-elimination from C---H bond in Mg+(CH3OH) n show that the reaction barriers flatten above 20 kcal/mol as n reaches 4 and above. These calculation results prove that the source of loss of H atom in ground state Mg+(CH3OH)n should be through the O---H bond rather than through the C---H bond. Compared to Mg+(CH3OH)n, the reaction barriers for H-elimination in Mg+(NH3)n is much larger, which is in consistent with the experimental observation of little H-elimination for Mg
International Nuclear Information System (INIS)
Holst, Bastian; French, Martin; Redmer, Ronald
2011-01-01
Using Kubo's linear response theory, we derive expressions for the frequency-dependent electrical conductivity (Kubo-Greenwood formula), thermopower, and thermal conductivity in a strongly correlated electron system. These are evaluated within ab initio molecular dynamics simulations in order to study the thermoelectric transport coefficients in dense liquid hydrogen, especially near the nonmetal-to-metal transition region. We also observe significant deviations from the widely used Wiedemann-Franz law, which is strictly valid only for degenerate systems, and give an estimate for its valid scope of application toward lower densities.
Magnuson, Martin; Mattesini, Maurizio; Bugnet, Matthieu; Eklund, Per
2015-01-01
The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr$_{2}$GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr$_{2}$GeC. The Cr $L_{2,3}$, C $K$, and Ge $M_{1}$, $M_{2,3}$ emission spectra are interpreted with first-principles density-functional theory (DFT)...
Ab initio study of He-He interactions in homogeneous electron gas
Energy Technology Data Exchange (ETDEWEB)
Wang, Jinlong; Niu, Liang-Liang; Zhang, Ying, E-mail: zhyi@buaa.edu.cn
2017-02-15
Highlights: • Helium atoms interact via the He induced Friedel oscillations of electron densities. • He-He global binding energy minimum of ∼−0.09 eV is reached at an optimal electron density of 0.04 e/Å{sup 3}, corresponding to an optimal He-He separation of ∼1.7 Å. • The present results can qualitatively interpret the well-known He self-trapping behavior in metals. - Abstract: We have investigated the immersion energy of a single He and the He-He interactions in homogeneous electron gas using ab initio calculations. It is found that He dislikes electrons and He-He interact via the He induced Friedel oscillations of electron densities. A critical electron density at which the global binding energy extremum shifts from the first minimum to the second one is identified. We also discover that the He-He global binding energy minimum of ∼−0.09 eV is reached at an optimal electron density of 0.04 e/Å{sup 3}, corresponding to an optimal He-He separation of ∼1.7 Å. Further, the He atoms are found to gain a trivial amount of 2s and 2p states from the free electrons, inducing a hybridization between the He s- and p-states. The present results can qualitatively interpret the well-known He self-trapping behavior in metals.
Ab initio study of the electron-phonon coupling at the Cr(001) surface
Peters, L.; Rudenko, A. N.; Katsnelson, M. I.
2018-04-01
It is experimentally well established that the Cr(001) surface exhibits a sharp resonance around the Fermi level. However, there is no consensus about its physical origin. It is proposed to be either due to a single particle dz2 surface state renormalized by electron-phonon coupling or the orbital Kondo effect involving the degenerate dx z/ dy z states. In this paper we examine the electron-phonon coupling of the Cr(001) surface by means of ab-initio calculations in the form of density functional perturbation theory. More precisely, the electron-phonon mass-enhancement factor of the surface layer is investigated for the 3d states. For the majority and minority spin dz2 surface states we find values of 0.19 and 0.16. We show that these calculated electron-phonon mass-enhancement factors are not in agreement with the experimental data even if we use realistic values for the temperature range and surface Debye frequency for the fit of the experimental data. More precisely, then experimentally an electron-phonon mass-enhancement factor of 0.70 ±0.10 is obtained, which is not in agreement with our calculated values of 0.19 and 0.16. Our findings suggest that the experimentally observed resonance at the Cr(001) surface is not due to electron-phonon effects but due to electron-electron correlation effects.
Phase stability and electronic structure of transition-metal aluminides
International Nuclear Information System (INIS)
Carlsson, A.E.
1992-01-01
This paper will describe the interplay between die electronic structure and structural energetics in simple, complex, and quasicrystalline Al-transition metal (T) intermetallics. The first example is the Ll 2 -DO 22 competition in Al 3 T compounds. Ab-initio electronic total-energy calculations reveal surprisingly large structural-energy differences, and show that the phase stability of both stoichiometric and ternary-substituted compounds correlates closely with a quasigap in the electronic density of states (DOS). Secondly, ab-initio calculations for the structural stability of the icosahedrally based Al 12 W structure reveal similar quasigap effects, and provide a simple physical explanation for the stability of the complex aluminide structures. Finally, parametrized tight-binding model calculations for the Al-Mn quasicrystal reveal a large spread in the local Mn DOS behavior, and support a two-site model for the quasicrystal's magnetic behavior
Erum, Nazia; Azhar Iqbal, Muhammad
2017-09-01
Detailed ab-initio calculations are performed to investigate structural, elastic, mechanical, magneto-electronic and optical properties of the KXF3 (X = V, Fe, Co, Ni) fluoro-perovskites using Full Potential Linearized Augmented Plane Wave (FP-LAPW) method within the framework of density functional theory (DFT). The calculated structural parameters by DFT and analytical methods are found consistent with the experimental results. From the elastic and mechanical properties, it can be inferred that these compounds are elastically stable and anisotropic while KCoF3 is harder than rest of the compounds. Furthermore, thermal behavior of these compounds is analyzed by calculating Debye temperature (θD). The calculated spin dependent magneto-electronic properties in these compounds reveal that exchange splitting is dominated by N-3d orbital. The stable magnetic phase optimizations verify the experimental observations at low temperature. Type of chemical bonding is analyzed with the help of variations in electron density difference distribution that is induced due to changes of the second cation. The linear optical properties are also discussed in terms of optical spectra. The present methodology represents an influential approach to calculate the whole set of mechanical and magneto-opto-electronic parameters, which would support to understand various physical phenomena and empower device engineers for implementing these materials in spintronic applications.
Magnuson, Martin; Mattesini, Maurizio; Bugnet, Matthieu; Eklund, Per
2015-10-01
The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L 2, 3, C K, and Ge M 1, M 2, 3 emission spectra are interpreted with first-principles density-functional theory (DFT) including core-to-valence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should affect the thermal expansion coefficient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.
Electronic structure and superconductivity of MgB 2
Indian Academy of Sciences (India)
Results of ab initio electronic structure calculations on the compound, MgB2, using the FPLAPW method employing GGA for the exchange–correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with ...
Ab Initio Modeling of Structure and Properties of Single and Mixed Alkali Silicate Glasses.
Baral, Khagendra; Li, Aize; Ching, Wai-Yim
2017-10-12
A density functional theory (DFT)-based ab initio molecular dynamics (AIMD) has been applied to simulate models of single and mixed alkali silicate glasses with two different molar concentrations of alkali oxides. The structural environments and spatial distributions of alkali ions in the 10 simulated models with 20% and 30% of Li, Na, K and equal proportions of Li-Na and Na-K are studied in detail for subtle variations among the models. Quantum mechanical calculations of electronic structures, interatomic bonding, and mechanical and optical properties are carried out for each of the models, and the results are compared with available experimental observation and other simulations. The calculated results are in good agreement with the experimental data. We have used the novel concept of using the total bond order density (TBOD), a quantum mechanical metric, to characterize internal cohesion in these glass models. The mixed alkali effect (MAE) is visible in the bulk mechanical properties but not obvious in other physical properties studied in this paper. We show that Li doping deviates from expected trend due to the much stronger Li-O bonding than those of Na and K doping. The approach used in this study is in contrast with current studies in alkali-doped silicate glasses based only on geometric characterizations.
Quantum mechanical ab initio simulation of the electron screening effect in metal deuteride crystals
Energy Technology Data Exchange (ETDEWEB)
Huke, A.; Chun, S.M.; Biller, A.; Heide, P. [Technische Universitaet Berlin, Institut fuer Optik und Atomare Physik, Berlin (Germany); Czerski, K. [Technische Universitaet Berlin, Institut fuer Optik und Atomare Physik, Berlin (Germany); University of Szczecin, Institute of Physics, Szczecin (Poland)
2008-02-15
In antecedent experiments the electron screening energies of the d+d reactions in metallic environments have been determined to be enhanced by an order of magnitude in comparison to the case of gaseous deuterium targets. The analytical models describing averaged material properties have not been able to explain the experimental results so far. Therefore, a first effort has been undertaken to simulate the dynamics of reacting deuterons in a metallic lattice by means of an ab initio Hartree-Fock calculation of the total electrostatic force between the lattice and the successively approaching deuterons via path integration. The calculations have been performed for Li and Ta, clearly showing a migration of electrons from host metallic to the deuterium atoms. However, in order to avoid more of the necessary simplifications in the model the utilization of a massive parallel supercomputer would be required. (orig.) 3.
Ab Initio Calculations on Halogen Bond Between N-Br and Electron-donating Groups
Institute of Scientific and Technical Information of China (English)
WANG Yan-hua; CHEN Xue-song; ZOU Jian-wei; YU Qing-sen
2007-01-01
Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ* to gain a deeper insight into the nature of the N-Br halogen stronger halogen-bonding complex than the C-Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N＞O＞S; O(sp3)＞O(sp2), which is adequate for the C-Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X-3 with N-bromosuccinimide are markedly lower than that of the corresponding X- with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosuccinimide. AIM analyses further confirmed the above results.
Electronic structure of incident carbon ions on a graphite surface
International Nuclear Information System (INIS)
Kiuchi, Masato; Takeuchi, Takae; Yamamoto, Masao.
1997-01-01
The electronic structure of an incident carbon ion on a graphite surface is discussed on the basis of ab initio molecular orbital calculations. A carbon cation forms a covalent bond with the graphite, and a carbon nonion is attracted to the graphite surface through van der Waals interaction. A carbon anion has no stable state on a graphite surface. The charge effects of incident ions become clear upon detailed examination of the electronic structure. (author)
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, K. A.
2000-01-01
The three lowest-lying electronic states of RuC, (1)Sigma(+), (3)Delta, and (1)Delta, have been investigated by performing all-electron ab initio multi-configuration self-consistent-field (CASSCF) and multi-reference configuration interaction (MRCI) calculations including relativistic corrections....... The electronic ground state is derived as (1)Sigma(+) with the spectroscopic constants r(e) = 1.616 Angstrom and omega(e) = 1085 cm(-1). The lowest-lying excited state, (3)Delta, has r(e) = 1.632 Angstrom, omega(e) = 1063 cm(-1), and T-e = 912 cm(-1). These results are consistent with recent spectroscopic values....... The chemical bonds in all three lowest-lying states are triple bonds composed of one sigma and two pi bonds. (C) 2000 Elsevier Science B.V. All rights reserved....
Arockia Doss, M; Savithiri, S; Rajarajan, G; Thanikachalam, V; Anbuselvan, C
2015-12-05
FT-IR and FT-Raman spectra of 3-pentyl-2,6-di(furan-2-yl) piperidin-4-one (3-PFPO) were recorded in the solid phase. The structural and spectroscopic analyses of 3-PFPO were made by using B3LYP/HF level with 6-311++G(d, p) basis set. The fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Comparison of the observed fundamental vibrational frequencies of 3-PFPO with calculated results by HF and DFT methods indicates that B3LYP is superior to HF method for molecular vibrational problems. The electronic properties such as excitation energies, oscillator strength, wavelengths and HOMO-LUMO energies were obtained by time-dependent DFT (TD-DFT) approach. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The hyperconjugative interaction energy (E((2))) and electron densities of donor (i) and acceptor (j) bonds were calculated using NBO analysis. In addition, MEP and atomic charges of carbon, nitrogen, oxygen and hydrogen were calculated using B3LYP/6-311++G(d, p) level theory. Moreover, thermodynamic properties (heat capacities, entropy and enthalpy) of the title compound at different temperatures were calculated in gas phase. Copyright © 2015 Elsevier B.V. All rights reserved.
Bokarev, Sergey I; Dantz, Marcus; Suljoti, Edlira; Kühn, Oliver; Aziz, Emad F
2013-08-23
Nonradiative decay channels in the L-edge fluorescence yield spectra from transition-metal-aqueous solutions give rise to spectral distortions with respect to x-ray transmission spectra. Their origin is unraveled here using partial and inverse partial fluorescence yields on the microjet combined with multireference ab initio electronic structure calculations. Comparing Fe2+, Fe3+, and Co2+ systems we demonstrate and quantify unequivocally the state-dependent electron delocalization within the manifold of d orbitals as one origin of this observation.
Unraveling the structure of the h-BN/Rh(111) nanomesh with ab initio calculations
International Nuclear Information System (INIS)
Laskowski, R; Blaha, P
2008-01-01
The properties of a single layer of h-BN on top of a Rh(111) surface are discussed in terms of an ab initio generated force field approach as well as by direct ab initio density-functional theory (DFT) calculations. A single-layer model for the h-BN/Rh(111) nanomesh, in contrast to a previously considered (incomplete) double-layer model of h-BN, can explain the experimental data. The main focus of this work is to compare a force field approach described earlier in (Laskowski et al 2007 Phys. Rev. Lett. 98 106802) with direct ab initio calculations. The calculated geometry of the h-BN layer is very similar to the structure predicted by the force field approach. The ab initio calculated density of states projected on N-p x,y of BN corresponding to 'low' and 'high' regions with respect to the Rh surface shows a 1 eV splitting and thus explains the observed σ-band splitting. Moreover, we find good agreement between calculated and experimental scanning tunneling microscope (STM) images of this system
Energy Technology Data Exchange (ETDEWEB)
Matar, Samir F. [CNRS, ICMCB, UPR 9048, F‐33600 Pessac (France); Université de Bordeaux, ICMCB, UPR 9048, F‐33600 Pessac (France); Al-Alam, Adel; Ouaini, Naïm [Université Saint-Esprit de Kaslik (USEK), Groupe OCM (Optimization et Caractérisation des Matériaux), CSR-USEK, CNRS-L, Jounieh (Lebanon); Pöttgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstraße 30, D-48149 Münster (Germany)
2013-06-15
The electronic structures of the metal-rich phosphides LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7} were studied by DFT calculations. Both phosphides consist of three-dimensional [Co{sub 6}P{sub 4}] and [Co{sub 12}P{sub 7}] polyanionic networks which leave hexagonal channels for the lithium atoms. COOP data show strong Co–P and Co–Co bonding within the polyanions. The lithium atoms have trigonal prismatic phosphorus coordination. Total energy calculations indicate stability upon de-lithiation towards the Co{sub 6}P{sub 4} and Co{sub 12}P{sub 7} substructures - Graphical abstract: The cobalt–phosphorus networks in LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}. - Highlights: • Chemical bonding resolved in the metal-rich phosphides LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}. • Strong covalent Co–P bonding character in the [Co{sub 6}P{sub 4}] and [Co{sub 12}P{sub 7}] substructures. • Total energy calculations indicate stability of the de-lithiated substructures.
International Nuclear Information System (INIS)
CalderIn, L; Gonzalez, L E; Gonzalez, D J
2011-01-01
Fluid Hg undergoes a metal-nonmetal (M-NM) transition when expanded toward a density of around 9 g cm -3 . We have performed ab initio molecular dynamics simulations for several thermodynamic states around the M-NM transition range and the associated static, dynamic and electronic properties have been analyzed. The calculated static structure shows a good agreement with the available experimental data. It is found that the volume expansion decreases the number of nearest neighbors from 10 (near the triple point) to around 8 at the M-NM transition region. Moreover, these neighbors are arranged into two subshells and the decrease in the number of neighbors occurs in the inner subshell. The calculated dynamic structure factors agree fairly well with their experimental counterparts obtained by inelastic x-ray scattering experiments, which display inelastic side peaks. The derived dispersion relation exhibits some positive dispersion for all the states, although its value around the M-NM transition region is not as marked as suggested by the experiment. We have also calculated the electronic density of states, which shows the appearance of a gap at a density of around 8.3 g cm -3 . (paper)
Accuracy of ab initio electron correlation and electron densities in vanadium dioxide
Kylänpää, Ilkka; Balachandran, Janakiraman; Ganesh, Panchapakesan; Heinonen, Olle; Kent, Paul R. C.; Krogel, Jaron T.
2017-11-01
Diffusion quantum Monte Carlo results are used as a reference to analyze properties related to phase stability and magnetism in vanadium dioxide computed with various formulations of density functional theory. We introduce metrics related to energetics, electron densities and spin densities that give us insight on both local and global variations in the antiferromagnetic M1 and R phases. Importantly, these metrics can address contributions arising from the challenging description of the 3 d orbital physics in this material. We observe that the best description of energetics between the structural phases does not correspond to the best accuracy in the charge density, which is consistent with observations made recently by Medvedev et al. [Science 355, 371 (2017), 10.1126/science.aag0410] in the context of isolated atoms. However, we do find evidence that an accurate spin density connects to correct energetic ordering of different magnetic states in VO2, although local, semilocal, and meta-GGA functionals tend to erroneously favor demagnetization of the vanadium sites. The recently developed SCAN functional stands out as remaining nearly balanced in terms of magnetization across the M1-R transition and correctly predicting the ground state crystal structure. In addition to ranking current density functionals, our reference energies and densities serve as important benchmarks for future functional development. With our reference data, the accuracy of both the energy and the electron density can be monitored simultaneously, which is useful for functional development. So far, this kind of detailed high accuracy reference data for correlated materials has been absent from the literature.
Ab-initio electronic and magnetic properties of Fe-Al alloys
Directory of Open Access Journals (Sweden)
Apiñaniz, E.
2000-06-01
Full Text Available This work presents ab-initio self-consistent calculations performed with the TB-LMTO code to study the different phases of the Fe-Al phase diagram, corresponding to the ordered structures B2, DO3 and B32 and for Fe50Al50 and Fe3Al compositions. Both, unpolarized and spin-polarized calculations have been performed to deduce the energetic difference between the paramagnetic and ferromagnetic state of the corresponding structure. Calculations for the disordered structures have also been performed for the previously mentioned compositions. These results show that by disordering the alloy magnetism is enhanced and that the equilibrium lattice parameter increases.
En este trabajo se presentan cálculos autoconsistentes ab-initio realizados con el método TB-LMTO (Tight Binding Linear Muffin Tin Orbital con el fin de estudiar las diferentes estructuras que se presentan en el diagrama de fases de las aleaciones Fe-Al. Se han estudiado las estructuras ordenadas B2, DO3 y B32 para las siguientes concentraciones: Fe50Al50 y Fe3Al. Asimismo, se han realizado cálculos teniendo y sin tener en cuenta la polarización de spin con el fin de poder deducir la diferencia energética entre los estados ferromágneticos y paramágneticos de la misma estructura. Por otra parte se han realizado estos mismos cálculos para estructuras desordenadas y las mismas concentraciones. Los resultados muestran que mediante el desorden aumenta el magnetismo de estas aleaciones y crece el parámetro de red.
Djordjević, Tijana; Radović, Ivan; Despoja, Vito; Lyon, Keenan; Borka, Duško; Mišković, Zoran L
2018-01-01
We present an analytical modeling of the electron energy loss (EEL) spectroscopy data for free-standing graphene obtained by scanning transmission electron microscope. The probability density for energy loss of fast electrons traversing graphene under normal incidence is evaluated using an optical approximation based on the conductivity of graphene given in the local, i.e., frequency-dependent form derived by both a two-dimensional, two-fluid extended hydrodynamic (eHD) model and an ab initio method. We compare the results for the real and imaginary parts of the optical conductivity in graphene obtained by these two methods. The calculated probability density is directly compared with the EEL spectra from three independent experiments and we find very good agreement, especially in the case of the eHD model. Furthermore, we point out that the subtraction of the zero-loss peak from the experimental EEL spectra has a strong influence on the analytical model for the EEL spectroscopy data. Copyright © 2017 Elsevier B.V. All rights reserved.
Electronic structure and optical properties of solid C60
International Nuclear Information System (INIS)
Mattesini, M.; Ahuja, R.; Sa, L.; Hugosson, H.W.; Johansson, B.; Eriksson, O.
2009-01-01
The electronic structure and the optical properties of face-centered-cubic C 60 have been investigated by using an all-electron full-potential method. Our ab initio results show that the imaginary dielectric function for high-energy values looks very similar to that of graphite, revealing close electronic structure similarities between the two systems. We have also identified the origin of different peaks in the dielectric function of fullerene by means of the calculated electronic density of states. The computed optical spectrum compares fairly well with the available experimental data for the Vis-UV absorption spectrum of solid C 60 .
Faas, S.; Snijders, Jaap; van Lenthe, J.H.; HernandezLaguna, A; Maruani, J; McWeeny, R; Wilson, S
2000-01-01
In this paper we present the first application of the ZORA (Zeroth Order Regular Approximation of the Dirac Fock equation) formalism in Ab Initio electronic structure calculations. The ZORA method, which has been tested previously in the context of Density Functional Theory, has been implemented in
Ab initio pseudopotential theory
International Nuclear Information System (INIS)
Yin, M.T.; Cohen, M.L.
1982-01-01
The ab initio norm-conserving pseudopotential is generated from a reference atomic configuration in which the pseudoatomic eigenvalues and wave functions outside the core region agree with the corresponding ab initio all-electron results within the density-functional formalism. This paper explains why such pseudopotentials accurately reproduce the all-electron results in both atoms and in multiatomic systems. In particular, a theorem is derived to demonstrate the energy- and perturbation-independent properties of ab initio pseudopotentials
Electronic structure and formation energy of a vacancy in aluminum
International Nuclear Information System (INIS)
Chakraborty, B.; Siegel, R.W.
1981-11-01
The electronic structure of a vacancy in Al was calculated self-consistently using norm-conserving ionic pseudopotentials obtained from ab initio atomic calculations. A 27-atom-site supercell containing 1 vacancy and 26 atoms was used to simulate the environment of the vacancy. A vacancy formation energy of 1.5 eV was also calculated (cf. the experimental value of 0.66 eV). The effects of the supercell and the nature of the ionic potential on the resulting electronic structure and formation energy are discussed. Results for the electronic structure of a divacancy are also presented. 3 figures
Computational prediction of muon stopping sites using ab initio random structure searching (AIRSS)
Liborio, Leandro; Sturniolo, Simone; Jochym, Dominik
2018-04-01
The stopping site of the muon in a muon-spin relaxation experiment is in general unknown. There are some techniques that can be used to guess the muon stopping site, but they often rely on approximations and are not generally applicable to all cases. In this work, we propose a purely theoretical method to predict muon stopping sites in crystalline materials from first principles. The method is based on a combination of ab initio calculations, random structure searching, and machine learning, and it has successfully predicted the MuT and MuBC stopping sites of muonium in Si, diamond, and Ge, as well as the muonium stopping site in LiF, without any recourse to experimental results. The method makes use of Soprano, a Python library developed to aid ab initio computational crystallography, that was publicly released and contains all the software tools necessary to reproduce our analysis.
Ab initio study on structural stability of uranium carbide
International Nuclear Information System (INIS)
Sahoo, B.D.; Joshi, K.D.; Gupta, Satish C.
2013-01-01
First principles calculations have been performed using plane wave pseudopotential and full potential linearized augmented plane wave (FP-LAPW) methods to analyze structural, elastic and dynamic stability of UC under hydrostatic compression. Our calculations within pseudopotential method suggest that the rocksalt (B1) structure will transform to body centered orthorhombic (bco) structure at ∼21.5 GPa. The FP-LAPW calculations put this transition at 23 GPa. The transition pressures determined from our calculations though agree reasonably with the experimental value of 27 GPa, the high pressure bco structure suggested by theory differs slightly from the experimentally reported pseudo bco phase. The elastic stability analysis of B1 phase suggests that the B1 to bco transition is driven by the failure of C 44 modulus. This finding is further substantiated by the lattice dynamic calculations which demonstrate that the B1 phase becomes dynamically unstable around the transition pressure and the instability is of long wavelength nature
International Nuclear Information System (INIS)
Manikandan, M.; Santhosh, M.; Rajeswarapalanichamy, R.
2016-01-01
Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of actinide carbides AnC (An=U, Np) for three different crystal structures, namely NaCl, CsCl and ZnS. Among the considered structures, NaCl structure is found to be the most stable structure for these carbides at normal pressure. A pressure induced structural phase transition from NaCl to ZnS is observed. The electronic structure reveals that these carbides are metals. The calculated elastic constants indicate that these carbides are mechanically stable at normal pressure.
A nonlocal, ab initio model of dissociative electron attachment and vibrational excitation of NO
International Nuclear Information System (INIS)
Trevisan, Cynthia S.; Houfek, Karel; Zhang, Zhiyong; Orel, Ann E.; McCurdy, C. William; Rescigno, Thomas N.
2005-01-01
We present the results of an ab initio study of elastic scattering and vibrational excitation of NO by electron impact in the loW--energy (0-2 eV) region where the cross sections are dominated by resonance contributions. The 3Sigma-, 1Delta and 1Sigma+ NO- resonance lifetimes are taken from our earlier study [Phys. Rev. A 69, 062711 (2004)], but the resonance energies used here are obtained from new configuration-interaction studies. Here we employ a more elaborate nonlocal treatment of the nuclear dynamics, which is found to remedy the principal deficiencies of the local complex potential model we employed in our earlier study, and gives cross sections in better agreement with the most recent experiments. We also present cross sections for dissociative electron attachment to NO leading to groundstate products. The calculations show that, while the peak cross sections starting from NO in its ground vibrational state are very small, the cross sections are extremely sensitive to vibrational excitation of the target and should be readily observable for target NO molecules excited to v = 10 and above
Ab-initio theoretical predictions of structural properties of semiconductors
International Nuclear Information System (INIS)
Rodriguez, C.O.; Peltzer y Blanca, E.L.; Cappannini, O.M.
1983-01-01
Calculations of the total energies of Si, GaP and C together with related structural properties are presented. The results show good agreement with experimental values (differences of less than 6%). They also agree with other recent theoretical results. Calculations for Si and GaP have already been reported and are given here as a reference. (L.C.) [pt
Ab-initio theoretical predictions of structure properties of semiconductors
International Nuclear Information System (INIS)
Rodriguez, C.O.; Peltzer y Blanca, E.L.; Cappannini, O.M.
1983-01-01
In this paper, calculations of the total energies and related structural properties of Si, GaP and C are presented showing good agreement with experimental values. The total energy is calculated within the local-density functional formalism using first principles non-local pseudopotentials. (A.C.A.S.) [pt
Structure of hydrogenated amorphous silicon from ab initio molecular dynamics
Energy Technology Data Exchange (ETDEWEB)
Buda, F. (Department of Physics, The Ohio State University, 174 West 18th Avenue, Columbus, Ohio (USA)); Chiarotti, G.L. (International School for Advanced Studies, Strada Costiera 11, I-34014 Trieste (Italy) Laboratorio Tecnologie Avanzate Superfici e Catalisi del Consorzio Interuniversitario Nazionale di Fisica della Materia, Padriciano 99, I-34012 Trieste (Italy)); Car, R. (International School for Advanced Studies, Strada Costiera 11, I-34014 Trieste (Italy) Institut Romard de Recherche Numerique en Physique des Materiaux, CH-1015 Lausanne, Switzerland Department of Condensed Matter Physics, University of Geneva, CH-1211 Geneva (Switzerland)); Parrinello, M. (IBM Research Division, Zurich Research Laboratory, CH-8803 Rueschlikon (Switzerland))
1991-09-15
We have generated a model of hydrogenated amorphous silicon by first-principles molecular dynamics. Our results are in good agreement with the available experimental data and provide new insight into the microscopic structure of this material. The calculation lends support to models in which monohydride complexes are prevalent, and indicates a strong tendency of hydrogen to form small clusters.
Ab initio structure determination via powder X-ray diffraction
Indian Academy of Sciences (India)
Unknown
Although the method of structure completion when once the starting model is provided is ... In this article a survey of the recent development in this area is ..... The Monte Carlo method 4,9 differs from the traditional approaches as it operates in.
Ab initio MCHF structural calculations of Mg-like cerium
Wajid, Abdul; Jabeen, S.; Husain, Abid
2018-05-01
Energy levels and emission line wavelengths of high-Z materials are useful for impurity diagnostics in the next generation fusion devices. For this here we have calculated E1, M2 transitions, oscillator strengths, and transition probabilities for transitions among the terms belonging to the 2p63s2, 2p63s3p, 2p63p2 and 2p63s3d for the Magnesium like cerium (Ce XLVII) using the GRASP2K package based on the fully relativistic multi-configuration Dirac-Fock method. The electron correlation effects, Breit interaction and quantum electrodynamics effects to the atomic state wave functions and the corresponding energies have been taken into account.
Electric dipole, polarizability and structure of cesium chloride clusters with one-excess electron
International Nuclear Information System (INIS)
Jraij, A.; Allouche, A.R.; Rabilloud, F.; Korek, M.; Aubert-Frecon, M.; Rayane, D.; Compagnon, I.; Antoine, R.; Broyer, M.; Dugourd, Ph.
2006-01-01
The measurement of the electric dipole of gas phase one-excess electron Cs n Cl n-1 clusters is reported together with a theoretical ab initio prediction of stable structures, dipole moments and electronic polarizabilities for these species in their ground state. Results are in agreement with NaCl cubic structures
Direct observations of the MOF (UiO-66) structure by transmission electron microscopy
Zhu, Liangkui
2013-01-01
As a demonstration of ab initio structure characterizations of nano metal organic framework (MOF) crystals by high resolution transmission electron microscopy (HRTEM) and electron diffraction tomography methods, a Zr-MOF (UiO-66) structure was determined and further confirmed by Rietveld refinements of powder X-ray diffraction. HRTEM gave direct imaging of the channels. © 2013 The Royal Society of Chemistry.
Ramsdellite-structured LiTiO 2: A new phase predicted from ab initio calculations
Koudriachova, M. V.
2008-06-01
A new phase of highly lithiated titania with potential application as an anode in Li-rechargeable batteries is predicted on the basis of ab initio calculations. This phase has a composition LiTiO2 and may be accessed through electrochemical lithiation of ramsdellite-structured TiO2 at the lowest potential reported for titanium dioxide based materials. The potential remains constant over a wide range of Li-concentrations. The new phase is metastable with respect to a tetragonally distorted rock salt structure, which hitherto has been the only known polymorph of LiTiO2.
Directory of Open Access Journals (Sweden)
Hirokazu Takaki
2014-01-01
Full Text Available We present an efficient computation technique for ab-initio electron transport calculations based on density functional theory and the nonequilibrium Green’s function formalism for application to heterostructures with two-dimensional (2D interfaces. The computational load for constructing the Green’s functions, which depends not only on the energy but also on the 2D Bloch wave vector along the interfaces and is thus catastrophically heavy, is circumvented by parallel computational techniques with the message passing interface, which divides the calculations of the Green’s functions with respect to energy and wave vectors. To demonstrate the computational efficiency of the present code, we perform ab-initio electron transport calculations of Al(100-Si(100-Al(100 heterostructures, one of the most typical metal-semiconductor-metal systems, and show their transmission spectra, density of states (DOSs, and dependence on the thickness of the Si layers.
International Nuclear Information System (INIS)
Spassova, Milena; Enchev, Venelin
2004-01-01
An ab initio HF and MP2 study of the static (hyper)polarizabilities of 2,4-substituted imidazoles and thiazoles is presented. The comparison of the two types of five-membered heterocycles suggests, that the exocyclic heteroatoms have much more influence upon the calculated hyperpolarizabilities, than the ring heteroatoms. It has been found, that adding diffuse functions to the 6-31G** basis set and inclusion of the electron correlation result in drastic changes in the second hyperpolarizability. The changes are more pronounced for the structures with larger number of sulfur atoms. A HF/6-31G** investigation of a push-pull system, in which thiorhodanine has been chosen as acceptor fragment shows an enhancement of the molecular polarizabilities with respect to the corresponding typical donor-acceptor NH 2 /NO 2 polyene
Bisri, Satria Zulkarnaen; Degoli, Elena; Spallanzani, Nicola; Krishnan, Gopi; Kooi, Bart Jan; Ghica, Corneliu; Yarema, Maksym; Heiss, Wolfgang; Pulci, Olivia; Ossicini, Stefano; Loi, Maria Antonietta
2014-08-27
Colloidal nanocrystals electronic energy levels are determined by strong size-dependent quantum confinement. Understanding the configuration of the energy levels of nanocrystal superlattices is vital in order to use them in heterostructures with other materials. A powerful method is reported to determine the energy levels of PbS nanocrystal assemblies by combining the utilization of electric-double-layer-gated transistors and advanced ab-initio theory. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Czech Academy of Sciences Publication Activity Database
Čársky, Petr
2010-01-01
Roč. 43, č. 17 (2010), s. 175204 ISSN 0953-4075 R&D Projects: GA MŠk OC09079; GA MŠk(CZ) OC10046; GA ČR GA202/08/0631 Institutional research plan: CEZ:AV0Z40400503 Keywords : ab initio calculations * electron scattering * polyatomic molecules Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.902, year: 2010
Ab-initio study of magnetism behavior in TiO{sub 2} semiconductor with structural defects
Energy Technology Data Exchange (ETDEWEB)
Zarhri, Z., E-mail: z.zarhri@gmail.com; Houmad, M.; Ziat, Y.; El Rhazouani, O.; Slassi, A.; Benyoussef, A.; El Kenz, A.
2016-05-15
Magnetic, electronic and structural properties of titanium dioxide material with different structural defects are studied using the first-principles ab-initio calculations and the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA) method in connection with the local density approximation (LDA). We investigated all structural defects in rutile TiO{sub 2} such as Titanium interstitial (Ti{sub i}), Titanium anti-sites (Ti{sub o}), Titanium vacancies (V{sub Ti}), Oxygen interstitial (O{sub i}), Oxygen anti-sites (O{sub Ti}) and oxygen vacancies (V{sub o}). Mechanisms of hybridization and interaction between magnetic atoms are investigated. The transition temperature is computed using the Mean Field Approximation (MFA).Magnetic stability energy of ferromagnetic and disordered local moment states is calculated to determine the most stable state. Titanium anti-sites have a half-metallic aspect. We also studied the change type caused by structural defects in this material. - Highlights: • Green function technique is used to study disordered systems. • We used DFT to study electronic structure of TiO{sub 2} perturbed by defects. • TiO{sub 2} with titanium antisite defect posesses a magnetic behavior. • The transition temperature is computed using the Mean Field Approximation.
Ab initio study of structural and mechanical property of solid molecular hydrogens
Ye, Yingting; Yang, Li; Yang, Tianle; Nie, Jinlan; Peng, Shuming; Long, Xinggui; Zu, Xiaotao; Du, Jincheng
2015-06-01
Ab initio calculations based on density functional theory (DFT) were performed to investigate the structural and the elastic properties of solid molecular hydrogens (H2). The influence of molecular axes of H2 on structural relative stabilities of hexagonal close-packed (hcp) and face-centered cubic (fcc) structured hydrogen molecular crystals were systematically investigated. Our results indicate that for hcp structures, disordered hydrogen molecule structure is more stable, while for fcc structures, Pa3 hydrogen molecular crystal is most stable. The cohesive energy of fcc H2 crystal was found to be lower than hcp. The mechanical properties of fcc and hcp hydrogen molecular crystals were obtained, with results consistent with previous theoretical calculations. In addition, the effects of zero point energy (ZPE) and van der Waals (vdW) correction on the cohesive energy and the stability of hydrogen molecular crystals were systematically studied and discussed.
Ab initio study of isomerism in molecular Li2AB+ ions with 12 and 14 valence electrons
International Nuclear Information System (INIS)
Charkin, O.P.; Klimenko, N.M.; Mak-Ki, M.L.; Shlojer, P.R.
1997-01-01
Ab initio calculations of potential energy surfaces (PES) of molecular ions Li 2 AB + with 12 and 14 valence electrons have been made in the framework of approximations MP2/6-31G*//HF/6-31G*+ZPE(HF/6-31G*) and MP4SDTQ/6-31*//MP2/6-31G*+ZPE(MP2/6-31G*). The following most favourable structures have been found: a double-terminal linear for LiNO + (a triplet); a plane bicyclic one for Li 2 OF + , Li 2 SCl + , Li 2 NO + (a singlet) and Li 2 PS + (a singlet), where both cations are coordinated to A-B bond; rectangular (T-shaped) for Li 2 OCl + and SFLi + , as well as for LiNS + and POLi 2 + ions in singlet and triplet states; in the form of a half-opened butterfly for Li 2 PS + (a triplet) and Li 2 SCl +
International Nuclear Information System (INIS)
Yamamoto, S.; Yamaguchi, K.; Nasu, K.
1990-01-01
Ab initio molecular-orbital calculations for CuO 6 clusters have been performed to elucidate the electronic structures of undoped and doped copper oxides, which are of current interest in relation to high-T c superconductivity. The electron correlation effects for these species are thoroughly investigated by the full-valence configuration-interaction method and the complete-active-space self-consistent-field method. The electron correlation effect is relatively simple for the A g state (σ hole), whereas pair excitations and spin-flip excitations give sizable contributions to the configuration-interaction wave function for the B state (in-plane π hole). Implications of these results are discussed in relation to the mechanisms of the high-T c superconductivity
International Nuclear Information System (INIS)
Goumri-Said, Souraya; Kanoun, Mohammed Benali
2010-01-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties.
Goumri-Said, Souraya
2010-08-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties. © 2010 Elsevier B.V. All rights reserved.
Sumowski, Chris Vanessa; Hanni, Matti; Schweizer, Sabine; Ochsenfeld, Christian
2014-01-14
The structural sensitivity of NMR chemical shifts as computed by quantum chemical methods is compared to a variety of empirical approaches for the example of a prototypical peptide, the 38-residue kaliotoxin KTX comprising 573 atoms. Despite the simplicity of empirical chemical shift prediction programs, the agreement with experimental results is rather good, underlining their usefulness. However, we show in our present work that they are highly insensitive to structural changes, which renders their use for validating predicted structures questionable. In contrast, quantum chemical methods show the expected high sensitivity to structural and electronic changes. This appears to be independent of the quantum chemical approach or the inclusion of solvent effects. For the latter, explicit solvent simulations with increasing number of snapshots were performed for two conformers of an eight amino acid sequence. In conclusion, the empirical approaches neither provide the expected magnitude nor the patterns of NMR chemical shifts determined by the clearly more costly ab initio methods upon structural changes. This restricts the use of empirical prediction programs in studies where peptide and protein structures are utilized for the NMR chemical shift evaluation such as in NMR refinement processes, structural model verifications, or calculations of NMR nuclear spin relaxation rates.
Ab Initio Study of Electronic Excitation Effects on SrTiO_{3}
Energy Technology Data Exchange (ETDEWEB)
Zhao, Shijun [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Zhang, Yanwen [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States); Weber, William J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
2017-11-14
Interaction of energetic ions or lasers with solids often induces electronic excitations that may modify material properties significantly. In this study, effects of electronic excitations on strontium titanate SrTiO_{3} (STO) are investigated based on first-principles calculations. The lattice structure, electronic properties, lattice vibrational frequencies, and dynamical stabilities are studied in detail. The results suggest that electronic excitation induces charge redistribution that is mainly observed in Ti–O bonds. The electronic band gap increases with increasing electronic excitation, as excitation mainly induces depopulation of Ti 3d states. Phonon analysis indicates that there is a large phonon band gap induced by electronic excitation because of the changes in the vibrational properties of Ti and O atoms. In addition, a new peak appears in the phonon density of states with imaginary frequencies, an indication of lattice instability. Further dynamics simulations confirm that STO undergoes transition to an amorphous structure under strong electronic excitations. In conclusion, the optical properties of STO under electronic excitation are consistent with the evolution of atomic and electronic structures, which suggests a possibility to probe the properties of STO in nonequilibrium state using optical measurement.
Simple synthesis, structure and ab initio study of 1,4-benzodiazepine-2,5-diones
Jadidi, Khosrow; Aryan, Reza; Mehrdad, Morteza; Lügger, Thomas; Ekkehardt Hahn, F.; Ng, Seik Weng
2004-04-01
A simple procedure for the synthesis of pyrido[2,1-c][1,4] benzodiazepine-6,12-dione ( 1) and 1,4-benzodiazepine-2,5-diones ( 2a- 2d), using microwave irradiation and/or conventional heating is reported. The configuration of 1 was determined by single-crystal X-ray diffraction. A detailed ab initio B3LYP/6-31G* calculation of structural parameters and substituent effects on ring inversion barriers (Δ G#) and also free energy differences (Δ G0) for benzodiazepines are reported.
Electronic structure of silicene
International Nuclear Information System (INIS)
Voon, L. C. Lew Yan
2015-01-01
In this topical review, we discuss the electronic structure of free-standing silicene by comparing results obtained using different theoretical methods. Silicene is a single atomic layer of silicon similar to graphene. The interest in silicene is the same as for graphene, in being two-dimensional and possessing a Dirac cone. One advantage of silicene is due to its compatibility with current silicon electronics. Both empirical and first-principles techniques have been used to study the electronic properties of silicene. We will provide a brief overview of the parameter space for first-principles calculations. However, since the theory is standard, no extensive discussion will be included. Instead, we will emphasize what empirical methods can provide to such investigations and the current state of these theories. Finally, we will review the properties computed using both types of theories for free-standing silicene, with emphasis on areas where we have contributed. Comparisons to graphene is provided throughout. (topical review)
Integration of QUARK and I-TASSER for Ab Initio Protein Structure Prediction in CASP11.
Zhang, Wenxuan; Yang, Jianyi; He, Baoji; Walker, Sara Elizabeth; Zhang, Hongjiu; Govindarajoo, Brandon; Virtanen, Jouko; Xue, Zhidong; Shen, Hong-Bin; Zhang, Yang
2016-09-01
We tested two pipelines developed for template-free protein structure prediction in the CASP11 experiment. First, the QUARK pipeline constructs structure models by reassembling fragments of continuously distributed lengths excised from unrelated proteins. Five free-modeling (FM) targets have the model successfully constructed by QUARK with a TM-score above 0.4, including the first model of T0837-D1, which has a TM-score = 0.736 and RMSD = 2.9 Å to the native. Detailed analysis showed that the success is partly attributed to the high-resolution contact map prediction derived from fragment-based distance-profiles, which are mainly located between regular secondary structure elements and loops/turns and help guide the orientation of secondary structure assembly. In the Zhang-Server pipeline, weakly scoring threading templates are re-ordered by the structural similarity to the ab initio folding models, which are then reassembled by I-TASSER based structure assembly simulations; 60% more domains with length up to 204 residues, compared to the QUARK pipeline, were successfully modeled by the I-TASSER pipeline with a TM-score above 0.4. The robustness of the I-TASSER pipeline can stem from the composite fragment-assembly simulations that combine structures from both ab initio folding and threading template refinements. Despite the promising cases, challenges still exist in long-range beta-strand folding, domain parsing, and the uncertainty of secondary structure prediction; the latter of which was found to affect nearly all aspects of FM structure predictions, from fragment identification, target classification, structure assembly, to final model selection. Significant efforts are needed to solve these problems before real progress on FM could be made. Proteins 2016; 84(Suppl 1):76-86. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
International Nuclear Information System (INIS)
Masrour, R.; Jabar, A.; Hlil, E.K.; Hamedoun, M.; Benyoussef, A.; Hourmatallah, A.; Rezzouk, A.; Bouslykhane, K.; Benzakour, N.
2017-01-01
Self-consistent ab initio calculations, based on Density Functional Theory (DFT) approach and using Full potential Linear Augmented Plane Wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Mn 2 NiAl. Magnetic moment considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for Monte Carlo simulations to compute other magnetic parameters. Also, the magnetic properties of Mn 2 NiAl are studied using the Monte Carlo simulations. The variation of magnetization and magnetic susceptibility with the reduced temperature of Mn 2 NiAl are investigated. The transition temperature of this system is deduced for different values exchange interaction and crystal field. The thermal total magnetization has been obtained, and the magnetic hysteresis cycle is established. The total magnetic moment is superior to those obtained by the other method and is mainly determined by the antiparallel aligned Mn I , Mn II and Ni spin moments. The superparamagnetic phase is found at the neighborhood of transition temperature. - Highlights: • Ab initio calculations are used to study magnetic and electronic properties of Mn 2 NiX. • The transition temperature of Mn 2 NiX is established. • The magnetic hysteresis cycle of M n2 NiX (X = Al, Ga, In, Sn) is deduced. • The magnetic coercive field of Mn 2 NiX (X = Al, Ga, In, Sn) is given.
International Nuclear Information System (INIS)
Grosso, G.
1986-01-01
The aim of this chapter is to present, in detail, some theoretical methods used to calculate electronic band structures in crystals. The basic strategies employed to attack the problem of electronic-structure calculations are presented. Successive sections present the basic formulations of the tight-binding, orthogonalized-plane-wave, Green'sfunction, and pseudopotential methods with a discussion of their application to perfect solids. Exemplifications in the case of a few selected problems provide further insight by the author into the physical aspects of the different methods and are a guide to the use of their mathematical techniques. A discussion is offered of completely a priori Hartree-Fock calculations and attempts to extend them. Special aspects of the different methods are also discussed in light of recently published related work
Goumri-Said, Souraya; Kanoun, Mohammed
2010-01-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance
Evolution of local atomic structure during solidification of Al2Au liquid: An ab initio study
International Nuclear Information System (INIS)
Xiong, L.H.; Lou, H.B.; Wang, X.D.; Debela, T.T.; Cao, Q.P.; Zhang, D.X.; Wang, S.Y.; Wang, C.Z.; Jiang, J.Z.
2014-01-01
The local atomic structure evolution in Al 2 Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt–Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al 2 Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of 〈0, 4, 4, 0〉, 〈0, 3, 6, 0〉 and 〈0, 4, 4, 2〉 with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF 2 -type Al 2 Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al 2 Au alloy
Evolution of local atomic structure during solidification of Al2Au liquid: An ab initio study
Energy Technology Data Exchange (ETDEWEB)
Xiong, L H; Lou, H B; Wang, X D; Debela, T T; Cao, Q P; Zhang, D X; Wang, S Y; Wang, C Z; Jiang, J Z
2014-04-01
The local atomic structure evolution in Al2Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt-Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al2Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of < 0,4,4,0 >, < 0,3, 6,0 > and < 0,4,4,2 > with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF2-type Al2Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al2Au alloy. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Ab initio study of vibronic transitions between x2π and 12Σ+ electronic states of HCP+ ion
Directory of Open Access Journals (Sweden)
Stojanović Ljiljana
2013-01-01
Full Text Available The ground and low-lying excited doublet electronic states of the HCP+ ion were studied by means of multireference configuration interaction method. Vibronic energy levels of the X2Π state of Σ, Π, Δ, and Φ symmetry, up to the 2500 cm-1, have been calculated variationally, employing previously developed ab initio methods which take into account vibronic and spin-orbit interactions. Obtained vibronic wave functions were used to estimate transition moments between vibronic energy levels of the X2Π and 12Σ+ electronic states. Results were compared to available experimental and theoretical data. [Projekat Ministarstva nauke Republike Srbije, br. 172040
Ab initio calculation of the electronic and optical properties of solid pentacene
International Nuclear Information System (INIS)
Tiago, Murilo L.; Northrup, John E.; Louie, Steve G.
2002-01-01
The optical and electronic properties of crystalline pentacene are studied, using a first-principles Green's-function approach. The quasiparticle energies are calculated within the GW approximation and the electron-hole excitations are computed by solving the Bethe-Salpeter equation. We investigate the role of polymorphism on the electronic energy gap and linear optical spectrum by studying two different crystalline phases: the solution-phase structure and the vapor-phase structure. charge-transfer excitons are found to dominate the optical spectrum. Excitons with sizable binding energies are predicted for both phases
Band structure and unconventional electronic topology of CoSi
Pshenay-Severin, D. A.; Ivanov, Y. V.; Burkov, A. A.; Burkov, A. T.
2018-04-01
Semimetals with certain crystal symmetries may possess unusual electronic structure topology, distinct from that of the conventional Weyl and Dirac semimetals. Characteristic property of these materials is the existence of band-touching points with multiple (higher than two-fold) degeneracy and nonzero Chern number. CoSi is a representative of this group of materials exhibiting the so-called ‘new fermions’. We report on an ab initio calculation of the electronic structure of CoSi using density functional methods, taking into account the spin-orbit interactions. The linearized \
International Nuclear Information System (INIS)
Komaguchi, Kenji; Shiotani, Masaru; Ishikawa, Mitsuo
1995-01-01
The σ-type radical cations generated by one electron oxidation of the saturated hydrocarbon have been attracted much attention because of their fundamental importance as primary reactant species in radiation chemistry. Our studies on σ-type radical cations were recently extended to the silacyclohexane (cSiC5), silacyclopentane (cSiC4), and silacyclobutane (cSiC3) radical cations. Their electronic structure, dynamics, and reactions were investigated by means of low temperature matrix isolation ESR technique combined with ionizing radiation (γ-rays from 60 Co). In the preceding paper, the 1-methylsilacyclohexane (1-Me-cSiC5) radical cation has been found to take an asymmetrically distorted C 1 structure with one of two Si-C bonds elongated in which the unpaired electron mainly resides ( 2 A in C 1 ). This conclusion was based on the 4.2 K ESR spectra of radical cations of selectively deuteriated and/or methylsubstituted silacyclohexanes, i.e., cSiC5-2,2,6,6-d 4 + , 1-Me-cSiC5 + , 1-Me-cSiC5-2,2-d 2 + , 1-Me-cSiC5-2,2,6,6-d 4 + , 1,1-Me 2 -cSiC5 + , and 4,4-Me 2 -cSiC5 + , in a frozen CF 3 -cC 6 F 11 matrix. Here we report further experimental and theoretical results on 1-methylsilacyclohexane radical cation, especially on the ab initio MO results and matrix effects on the structural distortion, as well as thermal reactions of the radical cations. The results will make it clear that the distorted C 1 structure of the 1-Me-cSiC5 + is the intrinsic nature at the ground electronic state. (J.P.N.)
Vanicek, Jiri
2014-03-01
Rigorous quantum-mechanical calculations of coherent ultrafast electronic spectra remain difficult. I will present several approaches developed in our group that increase the efficiency and accuracy of such calculations: First, we justified the feasibility of evaluating time-resolved spectra of large systems by proving that the number of trajectories needed for convergence of the semiclassical dephasing representation/phase averaging is independent of dimensionality. Recently, we further accelerated this approximation with a cellular scheme employing inverse Weierstrass transform and optimal scaling of the cell size. The accuracy of potential energy surfaces was increased by combining the dephasing representation with accurate on-the-fly ab initio electronic structure calculations, including nonadiabatic and spin-orbit couplings. Finally, the inherent semiclassical approximation was removed in the exact quantum Gaussian dephasing representation, in which semiclassical trajectories are replaced by communicating frozen Gaussian basis functions evolving classically with an average Hamiltonian. Among other examples I will present an on-the-fly ab initio semiclassical dynamics calculation of the dispersed time-resolved stimulated emission spectrum of the 54-dimensional azulene. This research was supported by EPFL and by the Swiss National Science Foundation NCCR MUST (Molecular Ultrafast Science and Technology) and Grant No. 200021124936/1.
International Nuclear Information System (INIS)
Izquierdo, J.; Vega, A.; Balbas, L. C.; Sanchez-Portal, Daniel; Junquera, Javier; Artacho, Emilio; Soler, Jose M.; Ordejon, Pablo
2000-01-01
We present a theoretical study of the electronic and magnetic properties of iron systems in different environments: pure iron systems [dimer, bcc bulk, (100) surface, and free-standing iron monolayer], and low-dimensional iron systems deposited on Ag (100) surface (monoatomic linear wires, iron monolayer, planar, and three-dimensional clusters). Electronic and magnetic properties have been calculated using a recently developed total-energy first-principles method based on density-functional theory with numerical atomic orbitals as a basis set for the description of valence electrons and nonlocal pseudopotentials for the atomic core. The Kohn-Sham equations are solved self-consistently within the generalized gradient approximation for the exchange-correlation potential. Tests on the pseudopotential, the basis set, grid spacing, and k sampling are carefully performed. This technique, which has been proved to be very efficient for large nonmagnetic systems, is applied in this paper to calculate electronic and magnetic properties of different iron nanostructures. The results compare well with previous ab initio all-electron calculations and with experimental data. The method predicts the correct trends in the magnetic moments of Fe systems for a great variety of environments and requires a smaller computational effort than other ab initio methods. (c) 2000 The American Physical Society
Energy Technology Data Exchange (ETDEWEB)
Izquierdo, J. [Departamento de Fisica Teorica, Universidad de Valladolid, E-47011 Valladolid, (Spain); Vega, A. [Departamento de Fisica Teorica, Universidad de Valladolid, E-47011 Valladolid, (Spain); Balbas, L. C. [Departamento de Fisica Teorica, Universidad de Valladolid, E-47011 Valladolid, (Spain); Sanchez-Portal, Daniel [Department of Physics and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States); Junquera, Javier [Departamento de Fisica de la Materia Condensada, C-III, and Institut Nicolas Cabrera, Universidad Autonoma de Madrid, 28049 Madrid, (Spain); Artacho, Emilio [Departamento de Fisica de la Materia Condensada, C-III, and Institut Nicolas Cabrera, Universidad Autonoma de Madrid, 28049 Madrid, (Spain); Soler, Jose M. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Ordejon, Pablo [Institut de Ciencia de Materials de Barcelona (CSIC), Campus de la U.A.B., Bellaterra, E-08193 Barcelona, (Spain)
2000-05-15
We present a theoretical study of the electronic and magnetic properties of iron systems in different environments: pure iron systems [dimer, bcc bulk, (100) surface, and free-standing iron monolayer], and low-dimensional iron systems deposited on Ag (100) surface (monoatomic linear wires, iron monolayer, planar, and three-dimensional clusters). Electronic and magnetic properties have been calculated using a recently developed total-energy first-principles method based on density-functional theory with numerical atomic orbitals as a basis set for the description of valence electrons and nonlocal pseudopotentials for the atomic core. The Kohn-Sham equations are solved self-consistently within the generalized gradient approximation for the exchange-correlation potential. Tests on the pseudopotential, the basis set, grid spacing, and k sampling are carefully performed. This technique, which has been proved to be very efficient for large nonmagnetic systems, is applied in this paper to calculate electronic and magnetic properties of different iron nanostructures. The results compare well with previous ab initio all-electron calculations and with experimental data. The method predicts the correct trends in the magnetic moments of Fe systems for a great variety of environments and requires a smaller computational effort than other ab initio methods. (c) 2000 The American Physical Society.
Electronic structure of point defects in semiconductors
International Nuclear Information System (INIS)
Bruneval, Fabien
2014-01-01
This 'Habilitation a diriger des Recherches' memoir presents most of my scientific activities during the past 7 years, in the field of electronic structure calculations of defects in solids. Point defects (vacancies, interstitials, impurities) in functional materials are a key parameter to determine if these materials will actually fill the role they have been assigned or not. Indeed, the presence of defects cannot be avoided when the temperature is increased or when the material is subjected to external stresses, such as irradiation in the nuclear reactors and in artificial satellites with solar radiations. However, in many cases, defects are introduced in the materials on purpose to tune the electronic transport, optical or even magnetic properties. This procedure is called the doping of semiconductors, which is the foundation technique for transistors, diodes, or photovoltaic cells. However, doping is not always straightforward and unexpected features may occur, such as doping asymmetry or Fermi level pinning, which can only be explained by complex phenomena involving different types of defects or complexes of defects. In this context, the calculations of electronic structure ab initio is an ideal tool to complement the experimental observations, to gain the understanding of phenomena at the atomic level, and even to predict the properties of defects. The power of the ab initio calculations comes from their ability to describe any system of electrons and nuclei without any specific adjustment. But although there is a strong need for numerical simulations in this field, the ab initio calculations for defects are still under development as of today. The work presented in this memoir summarizes my contributions to methodological developments on this subject. These developments have followed two main tracks. The first topic is the better understanding of the unavoidable finite size effects. Indeed, defects in semiconductors or insulators are generally present in
2015-05-08
Supplementary material for “Finding the stable structures of N1−xWX with an ab - initio high-throughput approach” Michael J. Mehl∗ Center for...AND SUBTITLE Supplementary Material for ’Finding the Stable Structures of N1-xWX with an ab - initio High-throughput Approach’ 5a. CONTRACT NUMBER 5b...and J. Hafner, Ab initio molecular dynamics for open-shell transition metals, Phys. Rev. B 48, 13115–13118 (1993). 2 G. Kresse and J. Hafner, Ab initio
The electronic structures of solids
Coles, B R
2013-01-01
The Electronic Structures of Solids aims to provide students of solid state physics with the essential concepts they will need in considering properties of solids that depend on their electronic structures and idea of the electronic character of particular materials and groups of materials. The book first discusses the electronic structure of atoms, including hydrogen atom and many-electron atom. The text also underscores bonding between atoms and electrons in metals. Discussions focus on bonding energies and structures in the solid elements, eigenstates of free-electron gas, and electrical co
An ab initio model of electron transport in hematite (a-Fe2O3) basal planes
International Nuclear Information System (INIS)
Rosso, Kevin M.; Smith, Dayle MA; Dupuis, Michel
2003-01-01
Transport of conduction electrons through basal planes of the hematite lattice was modeled as a valence alternation of iron cations using ab initio molecular orbital calculations and electron transfer theory. A cluster approach was successfully implemented to compute electron transfer rate-controlling quantities such as the reorganization energy and electronic coupling matrix element. Localization of a conduction electron at an iron lattice site is accompanied by large iron/oxygen bond length increases that give rise to a large inner-sphere component of the reorganization energy. The interaction between the reactant and product electronic states in the crossing?point configuration is substantial and leads to an adiabatic electron transfer system. Electron transfer is predicted to possess a small positive activation energy that turns out to be in excellent agreement with values deduced from conductivity measurements. Measured electron mobility can be explained in terms of nearest neighbor electron hops without significant contribution from iron atoms further away. Comparison of the predicted maximum polaron binding energy with the predicted half bandwidth indicates compliance with the small polaron condition. Therefore the localized electron treatment is appropriate to describe electron transport in this system
Structural properties of iron nitride on Cu(100): An ab-initio molecular dynamics study
Heryadi, Dodi
2011-01-01
Due to their potential applications in magnetic storage devices, iron nitrides have been a subject of numerous experimental and theoretical investigations. Thin films of iron nitride have been successfully grown on different substrates. To study the structural properties of a single monolayer film of FeN we have performed an ab-initio molecular dynamics simulation of its formation on a Cu(100) substrate. The iron nitride layer formed in our simulation shows a p4gm(2x2) reconstructed surface, in agreement with experimental results. In addition to its structural properties, we are also able to determine the magnetization of this thin film. Our results show that one monolayer of iron nitride on Cu(100) is ferromagnetic with a magnetic moment of 1.67 μ B. © 2011 Materials Research Society.
Atomic and electronic structure of exfoliated black phosphorus
International Nuclear Information System (INIS)
Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre; Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J.
2015-01-01
Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO 3 or H 3 PO 3 during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time
Atomic and electronic structure of exfoliated black phosphorus
Energy Technology Data Exchange (ETDEWEB)
Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
2015-11-15
Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.
International Nuclear Information System (INIS)
Nakayama, Akira; Taketsugu, Tetsuya; Shiga, Motoyuki
2009-01-01
Efficiency of the ab initio hybrid Monte Carlo and ab initio path integral hybrid Monte Carlo methods is enhanced by employing an auxiliary potential energy surface that is used to update the system configuration via molecular dynamics scheme. As a simple illustration of this method, a dual-level approach is introduced where potential energy gradients are evaluated by computationally less expensive ab initio electronic structure methods. (author)
Electronic, vibrational and related properties of group IV metal oxides by ab initio calculations
International Nuclear Information System (INIS)
Leite Alves, H.W.; Silva, C.C.; Lino, A.T.; Borges, P.D.; Scolfaro, L.M.R.; Silva, E.F. da
2008-01-01
We present our theoretical results for the structural, electronic, vibrational and optical properties of MO 2 (M = Sn, Zr, Hf and Ti) obtained by first-principles calculations. Relativistic effects are demonstrated to be important for a realistic description of the detailed structure of the electronic frequency-dependent dielectric function, as well as of the carrier effective masses. Based on our results, we found that the main contribution of the high values calculated for the oxides dielectric constants arises from the vibrational properties of these oxides, and the vibrational static dielectric constant values diminish with increasing pressure
Nahar, S. N.
2003-01-01
Most astrophysical plasmas entail a balance between ionization and recombination. We present new results from a unified method for self-consistent and ab initio calculations for the inverse processes of photoionization and (e + ion) recombination. The treatment for (e + ion) recombination subsumes the non-resonant radiative recombination and the resonant dielectronic recombination processes in a unified scheme (S.N. Nahar and A.K. Pradhan, Phys. Rev. A 49, 1816 (1994);H.L. Zhang, S.N. Nahar, and A.K. Pradhan, J.Phys.B, 32,1459 (1999)). Calculations are carried out using the R-matrix method in the close coupling approximation using an identical wavefunction expansion for both processes to ensure self-consistency. The results for photoionization and recombination cross sections may also be compared with state-of-the-art experiments on synchrotron radiation sources for photoionization, and on heavy ion storage rings for recombination. The new experiments display heretofore unprecedented detail in terms of resonances and background cross sections and thereby calibrate the theoretical data precisely. We find a level of agreement between theory and experiment at about 10% for not only the ground state but also the metastable states. The recent experiments therefore verify the estimated accuracy of the vast amount of photoionization data computed under the OP, IP and related works. features. Present work also reports photoionization cross sections including relativistic effects in the Breit-Pauli R-matrix (BPRM) approximation. Detailed features in the calculated cross sections exhibit the missing resonances due to fine structure. Self-consistent datasets for photoionization and recombination have so far been computed for approximately 45 atoms and ions. These are being reported in a continuing series of publications in Astrophysical J. Supplements (e.g. references below). These data will also be available from the electronic database TIPTOPBASE (http://heasarc.gsfc.nasa.gov)
International Nuclear Information System (INIS)
Closser, Kristina D.; Head-Gordon, Martin; Gessner, Oliver
2014-01-01
The dynamics resulting from electronic excitations of helium clusters were explored using ab initio molecular dynamics. The simulations were performed with configuration interaction singles and adiabatic classical dynamics coupled to a state-following algorithm. 100 different configurations of He 7 were excited into the 2s and 2p manifold for a total of 2800 trajectories. While the most common outcome (90%) was complete fragmentation to 6 ground state atoms and 1 excited state atom, 3% of trajectories yielded bound, He 2 * , and <0.5% yielded an excited helium trimer. The nature of the dynamics, kinetic energy release, and connections to experiments are discussed
International Nuclear Information System (INIS)
Bako, Imre; Megyes, Tuende; Palinkas, Gabor
2005-01-01
In this work, we present a study on water-acetonitrile (AN) mixtures by molecular dynamics ab initio and X-ray diffraction techniques. Comparison of the experimental total G(r) functions of the mixtures with the results of molecular dynamics simulation shows an overall good agreement. The properties of hydrogen bonded clusters (water clusters, and water-AN clusters) in these mixtures have been determined. Two different types of AN-water dimers were identified by ab initio quantum chemical calculation. One of these structures proved to be a true H-bonded dimer and the other a dipole bound dimer
Electronic structure of divacancy-hydrogen complexes in silicon
International Nuclear Information System (INIS)
Coutinho, J; Torres, V J B; Jones, R; Oeberg, S; Briddon, P R
2003-01-01
Divacancy-hydrogen complexes (V 2 H and V 2 H 2 ) in Si are studied by ab initio modelling using large supercells. Here we pay special attention to their electronic structure, showing that these defects produce deep carrier traps. Calculated electrical gap levels indicate that V 2 H 2 is an acceptor, whereas V 2 H is amphoteric, with levels close to those of the well known divacancy. Finally our results are compared with the available data from deep level transient spectroscopy and electron paramagnetic resonance experiments
Electronic structure of superlattices of graphene and hexagonal boron nitride
Kaloni, Thaneshwor P.
2011-11-14
We study the electronic structure of superlattices consisting of graphene and hexagonal boron nitride slabs, using ab initio density functional theory. We find that the system favors a short C–B bond length at the interface between the two component materials. A sizeable band gap at the Dirac point is opened for superlattices with single graphene layers but not for superlattices with graphene bilayers. The system is promising for applications in electronic devices such as field effect transistors and metal-oxide semiconductors.
Electronic structure of superlattices of graphene and hexagonal boron nitride
Kaloni, Thaneshwor P.; Cheng, Yingchun; Schwingenschlö gl, Udo
2011-01-01
We study the electronic structure of superlattices consisting of graphene and hexagonal boron nitride slabs, using ab initio density functional theory. We find that the system favors a short C–B bond length at the interface between the two component materials. A sizeable band gap at the Dirac point is opened for superlattices with single graphene layers but not for superlattices with graphene bilayers. The system is promising for applications in electronic devices such as field effect transistors and metal-oxide semiconductors.
Energy Technology Data Exchange (ETDEWEB)
Sharma, Yamini, E-mail: sharma.yamini62@gmail.com [Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P. (India); Srivastava, Pankaj [Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P. (India)
2012-08-15
Spinel indium sulphide exists in three phases. The tetragonal {beta}-phase transforms to the cubic {alpha}-phase at 420 Degree-Sign C which further transforms to the trigonal {gamma}-phase at 754 Degree-Sign C. Due to wide energy bandgap, the phases of indium sulphide have possibilities of applications in photo-electrochemical solar cell devices as a replacement of toxic CdS. The electronic, optical and transport properties of the three phases have therefore been investigated using full potential linear augmented plane wave (FP-LAPW) + local orbitals (lo) scheme, in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) for the purpose of exchange-correlation energy functional. We present the structure, energy bands and density of states (DOS) for {alpha}-, {beta}- and {gamma}-phases. The partial density of states (PDOS) of {beta}-In{sub 2}S{sub 3} is in good agreement with experiment and earlier ab initio calculations. To obtain the fundamental characteristics of these phases we have analysed their linear optical properties such as the dynamic dielectric function in the energy range of 0-15 eV. From the dynamic dielectric function it is seen that there is no directional anisotropy for {alpha}-phase since the longitudinal and transverse components are almost identical, however the {beta} and {gamma}-phases show birefringence. The optical absorption profiles clearly indicate that {beta}-phase has possibility of greater multiple direct and indirect interband transitions in the visible regions compared to the other phases. To study the existence of interesting thermoelectric properties, transport properties like electrical and thermal conductivities, Seebeck and Hall coefficients etc. are also calculated. Good agreements are found with the available experimental results. -- Highlights: Black-Right-Pointing-Pointer The electronic properties of phases of In{sub 2}S{sub 3} have been investigated. Black-Right-Pointing-Pointer The
International Nuclear Information System (INIS)
Gil, T.J.; McCurdy, C.W.; Rescigno, T.N.; Lengsfield, B.H. III
1994-01-01
The authors are reporting results of ab-initio calculations of electron-impact excitation of water and methane occurring at scattering energies up to 60 eV. The authors consider dissociative excited states of both systems since the understanding of their chemistry has considerable importance in plasma technology and atmospheric research. In the case of methane the authors are dealing with the promotion of a valence electron into Rydberg orbitals, while in water the excited states have one electron in an antibonding unoccupied valence orbital and support Feshbach resonances. The authors discuss issues related to convergence of the close-coupling expansion in the case of Rydberg excitation, where the authors have coupled up to 16 channels. The practical realization of the calculation within the framework of the complex Kohn variational principle represents merging of quantum chemistry and quantum scattering theory and is also discussed
CONFOLD2: improved contact-driven ab initio protein structure modeling.
Adhikari, Badri; Cheng, Jianlin
2018-01-25
Contact-guided protein structure prediction methods are becoming more and more successful because of the latest advances in residue-residue contact prediction. To support contact-driven structure prediction, effective tools that can quickly build tertiary structural models of good quality from predicted contacts need to be developed. We develop an improved contact-driven protein modelling method, CONFOLD2, and study how it may be effectively used for ab initio protein structure prediction with predicted contacts as input. It builds models using various subsets of input contacts to explore the fold space under the guidance of a soft square energy function, and then clusters the models to obtain the top five models. CONFOLD2 obtains an average reconstruction accuracy of 0.57 TM-score for the 150 proteins in the PSICOV contact prediction dataset. When benchmarked on the CASP11 contacts predicted using CONSIP2 and CASP12 contacts predicted using Raptor-X, CONFOLD2 achieves a mean TM-score of 0.41 on both datasets. CONFOLD2 allows to quickly generate top five structural models for a protein sequence when its secondary structures and contacts predictions at hand. The source code of CONFOLD2 is publicly available at https://github.com/multicom-toolbox/CONFOLD2/ .
International Nuclear Information System (INIS)
Wang Yubing; Zhao Gang; Liu Changsong; Zhu Zhengang
2010-01-01
Using ab initio molecular dynamics simulations and inherent structure formalism, the local atomic structure and electronic properties of liquid Si 15 Te 85 alloy were studied at eight different temperatures from 673 to 1373 K. In comparison with available experimental data, our calculated structure factors are acceptable. With increasing temperature from 773 to 1173 K, the calculated total coordination number N Total increases gradually in contrast to the behavior of a classical isotropic fluid. Our results of pair-correlation functions, bond-angle distribution functions and angular limited triplet correlation functions suggest that the temperature-dependence of the preserved sp 3 hybridization of Si atoms and Peierls-type distorted local structure around Te atoms both play important roles in the structural change of Si 15 Te 85 characterized by thermodynamic anomalies.
Energy Technology Data Exchange (ETDEWEB)
Wang Yubing, E-mail: ybwang1985@gmail.co [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Post Office 1129, Hefei 230031 (China); Zhao Gang [Department of Physics and Electronic Engineering, Ludong University, Hongqi Road, No. 186, Yantai 264025 (China); Liu Changsong; Zhu Zhengang [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Post Office 1129, Hefei 230031 (China)
2010-01-15
Using ab initio molecular dynamics simulations and inherent structure formalism, the local atomic structure and electronic properties of liquid Si{sub 15}Te{sub 85} alloy were studied at eight different temperatures from 673 to 1373 K. In comparison with available experimental data, our calculated structure factors are acceptable. With increasing temperature from 773 to 1173 K, the calculated total coordination number N{sub Total} increases gradually in contrast to the behavior of a classical isotropic fluid. Our results of pair-correlation functions, bond-angle distribution functions and angular limited triplet correlation functions suggest that the temperature-dependence of the preserved sp{sup 3} hybridization of Si atoms and Peierls-type distorted local structure around Te atoms both play important roles in the structural change of Si{sub 15}Te{sub 85} characterized by thermodynamic anomalies.
DEFF Research Database (Denmark)
Åstrand, Per-Olof; Ramanujam, P.S.; Hvilsted, Søren
2000-01-01
Electronic excitation energies of 16 azobenzene dyes have been calculated by ab initio methods within the second-order polarization propagator approximation (SOPPA). Good agreement with expriment is found for the lowest singlet and triplet states for both the trans- and cis-azobenzene molecules......, the experimental singlet π → π* transitions are reproduced for a set of azobenzene dyes with different electron donor and acceptor groups and the correct shifts in excitation energy are obtained for the different substituents. It has also been demonstrated that ab initio methods can be used to determine suitable...
Research of electronic absorption spectra of benzazols derivatives by ab initio calculations
Irgibaeva, I. S.; Birimzhanova, D. A.; Barashkov, N. N.
Using the method of density functional theory in approximating B3LYP with the basis set 6-31G* the computations of structures and UV-vis spectra (TDDFT method) of benzazols derivatives were performed. The comparison of estimated electron spectra with the observed ones was made indicating good agreement of theoretically obtained results with experiment. Moreover these compounds have distinctive spectral-luminescent properties (large stokes shift) because of intramolecular proton transfer in excited state.
Plasmon Lifetime in K: A Case Study of Correlated Electrons in Solids Amenable to Ab Initio Theory
International Nuclear Information System (INIS)
Ku, W.; Eguiluz, A.G.
1999-01-01
We solve the puzzle posed by the anomalous dispersion of the plasmon linewidth in K via all-electron density-response calculations, performed within the framework of time-dependent density-functional theory. The key damping mechanism is shown to be decay into particle-hole pairs involving empty states of d symmetry. While the effect of many-particle correlations is small, the correlations built into the 'final-state' d bands play an important, and novel, role related to the phase-space complexity introduced by these flat bands. Our case study of plasmon lifetime in K illustrates the importance of ab initio paradigms for the study of excitations in correlated-electron systems. copyright 1999 The American Physical Society
International Nuclear Information System (INIS)
Harchaoui, N; Hellal, S; Grosdidier, B; Gasser, J G
2008-01-01
The physical properties of disordered matter depend on the 'atomic structure' i.e. the arrangement of the atoms. This arrangement is described by the structure factor S (q) in reciprocal space and by the pair correlation function g(r) in real space. The structure factor is obtained experimentally while the numerical simulation enables us to obtain the pair correlation function. Liquid sodium is one of the elements the most studied and one can wonder about new scientific contribution appropriateness. The majority of theoretical calculations are compared with the experiment of Waseda. However two other posterior measurements have been published and give different results, in particular with regard to the height of the first peak of the structure factor. Three models of pseudopotential are considered to describe the electron-ion interaction. The first is a local pseudopotential with the alternative known as 'individual' of the model suggested by Fiolhais et al. The second model considered is that of Bachelet et al. This one, ab-initio and 'norm conserving', is non local. The last model is that proposed by Shaw known as 'first principles' and 'energy dependent'. Various static dielectric functions characteristic of the effects of exchange and correlation have been used and developed by Hellal et al. We calculated the form factors (pseudopotential in reciprocal space) and deduce the normalized energy-wave-number characteristic F N (q), the interatomic pair potential V eff (r), then the pair correlation function g(r) by molecular dynamics. The structure factor S(q) is obtained by Fourier transform and is compared with the experiment. Our calculations with the Bachelet and Shaw pseudopotentials are close to the last experiments of Greenfield et al. and of Huijben et al. Our results are discussed
Electronic structure of the antiferromagnetic phase of Sr2Co2O5
International Nuclear Information System (INIS)
Pardo, V.; Botta, P.M.; Baldomir, D.; Rivas, J.; Pineiro, A.; Calle, C. de la; Alonso, J.A.; Arias, J.E.
2008-01-01
Ab initio calculations analyze the properties of the G-type antiferromagnetic Sr 2 Co 2 O 5 as a high-spin system. The description of the electronic structure is given; all the Co atoms are in a high-spin state with a small unquenched orbital angular momentum. Thermal analysis on a polycrystalline sample shows a magnetic phase transition at high temperatures
Miniworkshop on Methods of Electronic Structure Calculations and Working Group on Disordered Alloys
Andersen, O K; Mookerjee, A
1994-01-01
Developments in the density functional theory and the methods of electronic structure calculations have made it possible to carry out ab-initio studies of a variety of materials efficiently and at a predictable level. This book covers many of those state-of-the-art developments and their applications to ordered and disordered materials, surfaces and interfaces and clusters, etc.
Electronic and magnetic properties of modified silicene/graphene hybrid: Ab initio study
Energy Technology Data Exchange (ETDEWEB)
Chowdhury, Suman; Jana, Debnarayan, E-mail: cujanad@yahoo.com
2016-11-01
Among other two-dimensional (2D) novel materials, graphene and silicene both have drawn intense research interest among the researchers because they possess some unique intriguing properties which can change the scenario of the current electronic industry. In this work we have studied the electronic and the magnetic properties of a new kind of materials which is the hybrid of these two materials. Density functional theory (DFT) has been employed to calculate the relevant electronic and magnetic properties of this hybrid material. The pristine structure is modified by substitutional doping or by creating vacancy (Y-X, where one Y atom (Si or C) has been replaced by one X atom (B, N, Al, P or void)). The calculations have revealed that void systems are unstable while Si-B and Si-N are most stable ones. It has been noticed that some of these doped structures are magnetic in nature having induced mid-gap states in the system. In particular, Si-void structure is unstable yet it possess the highest magnetic moment of the order of 4 μ{sub B} (μ{sub B} being the Bohr magneton). The estimated band gaps of modified silicene/graphene hybrid from spin polarized partial density of states (PDOS) vary between 1.43–2.38 eV and 1.58–2.50 eV for spin-up and spin-down channel respectively. The implication of midgap states has been critically analysed in the light of magnetic nature. This study may be useful to build hybrid spintronic devices with controllable gap for spin up and spin down states. - Graphical abstract: We have studied the electronic and magnetic properties of silicene/graphene hybrid by employing density functional theory (DFT). - Highlights: • Electronic and magnetic properties of two dimensional graphene/silicene hybrid have been explored. • There is no magnetism in the system for a single carbon atom vacancy. • A net magnetic moment of 4.0 Bohr magneton is observed for a single silicon atom vacancy. • Unpaired electrons introduce mid-gap states which
SGO: A fast engine for ab initio atomic structure global optimization by differential evolution
Chen, Zhanghui; Jia, Weile; Jiang, Xiangwei; Li, Shu-Shen; Wang, Lin-Wang
2017-10-01
As the high throughout calculations and material genome approaches become more and more popular in material science, the search for optimal ways to predict atomic global minimum structure is a high research priority. This paper presents a fast method for global search of atomic structures at ab initio level. The structures global optimization (SGO) engine consists of a high-efficiency differential evolution algorithm, accelerated local relaxation methods and a plane-wave density functional theory code running on GPU machines. The purpose is to show what can be achieved by combining the superior algorithms at the different levels of the searching scheme. SGO can search the global-minimum configurations of crystals, two-dimensional materials and quantum clusters without prior symmetry restriction in a relatively short time (half or several hours for systems with less than 25 atoms), thus making such a task a routine calculation. Comparisons with other existing methods such as minima hopping and genetic algorithm are provided. One motivation of our study is to investigate the properties of magnetic systems in different phases. The SGO engine is capable of surveying the local minima surrounding the global minimum, which provides the information for the overall energy landscape of a given system. Using this capability we have found several new configurations for testing systems, explored their energy landscape, and demonstrated that the magnetic moment of metal clusters fluctuates strongly in different local minima.
Electronic and optical properties of graphene-like InAs: An ab initio study
Sohrabi, Leila; Boochani, Arash; Ali Sebt, S.; Mohammad Elahi, S.
2018-03-01
The present work initially investigates structural, optical, and electronic properties of graphene-like InAs by using the full potential linear augmented plane wave method in the framework of density functional theory and is then compared with the bulk Indium Arsenide in the wurtzite phase. The lattice parameters are optimized with GGA-PBE and LDA approximations for both 2D- and 3D-InAs. In order to study the electronic properties of graphene-like InAs and bulk InAs in the wurtzite phase, the band gap is calculated by GGA-PBG and GGA-EV approximations. Moreover, optical parameters of graphene-like InAs and bulk InAs such as the real and imaginary parts of dielectric function, electron energy loss function, refractivity, extinction and absorption coefficients, and optical conductivity are investigated. Plasmonic frequencies of 2D- and 3D-InAs are also calculated by using maximum electron energy loss function and the roots of the real part of the dielectric function.
Ab-initio theoretical study of electronic excitations and optical properties in nanostructures
Marchesín, Federico
2017-01-01
218 p. La miniaturización de los dispositivos electrónicos para la transferencia de información y procesado de señales ha impulsado el estudio de las propiedades electrónicas y la dinámica de excitaciones electrónicas en nanoestructuras. En particular, los cálculos ab-initio de las repuestas ópticas y los modos plasmónicos colectivos de nanoestructuras metálicas y de grafeno, han permitido profundizar en el conocimiento de la física y así poder avanzar hacia aplicaciones industriales en mu...
A theoretical-spectroscopy, ab initio-based study of the electronic ground state of 121SbH3
International Nuclear Information System (INIS)
Yurchenko, Sergei N.; Carvajal, Miguel; Yachmenev, Andrey; Thiel, Walter; Jensen, Per
2010-01-01
For the stibine isotopologue 121 SbH 3 , we report improved theoretical calculations of the vibrational energies below 8000 cm -1 and simulations of the rovibrational spectrum in the 0-8000 cm -1 region. The calculations are based on a refined ab initio potential energy surface and on a new dipole moment surface obtained at the coupled cluster CCSD(T) level. The theoretical results are compared with the available experimental data in order to validate the ab initio surfaces and the TROVE computational method [Yurchenko SN, Thiel W, Jensen P. J Mol Spectrosc 2007;245:126-40] for calculating rovibrational energies and simulating rovibrational spectra of arbitrary molecules in isolated electronic states. A number of predicted vibrational energies of 121 SbH 3 are provided in order to stimulate new experimental investigations of stibine. The local-mode character of the vibrations in stibine is demonstrated through an analysis of the results in terms of local-mode theory.
Zhang, Yang
2014-02-01
We develop and test a new pipeline in CASP10 to predict protein structures based on an interplay of I-TASSER and QUARK for both free-modeling (FM) and template-based modeling (TBM) targets. The most noteworthy observation is that sorting through the threading template pool using the QUARK-based ab initio models as probes allows the detection of distant-homology templates which might be ignored by the traditional sequence profile-based threading alignment algorithms. Further template assembly refinement by I-TASSER resulted in successful folding of two medium-sized FM targets with >150 residues. For TBM, the multiple threading alignments from LOMETS are, for the first time, incorporated into the ab initio QUARK simulations, which were further refined by I-TASSER assembly refinement. Compared with the traditional threading assembly refinement procedures, the inclusion of the threading-constrained ab initio folding models can consistently improve the quality of the full-length models as assessed by the GDT-HA and hydrogen-bonding scores. Despite the success, significant challenges still exist in domain boundary prediction and consistent folding of medium-size proteins (especially beta-proteins) for nonhomologous targets. Further developments of sensitive fold-recognition and ab initio folding methods are critical for solving these problems. Copyright © 2013 Wiley Periodicals, Inc.
Belmonte, Donato; Gatti, Carlo; Ottonello, Giulio; Richet, Pascal; Vetuschi Zuccolini, Marino
2016-11-10
Thermodynamic and thermophysical properties of Na 2 SiO 3 in the Cmc2 1 structural state are computed ab initio using the hybrid B3LYP density functional method. The static properties at the athermal limit are first evaluated through a symmetry-preserving relaxation procedure. The thermodynamic properties that depend on vibrational frequencies, viz., heat capacities, thermal expansion, thermal derivative of the bulk modulus, thermal correction to internal energy, enthalpy, and Gibbs free energy, are then computed in the framework of quasi-harmonic approximation. Acoustic branches are computed by solving the Christoffel determinant and are assumed to follow sine wave dispersion when traveling within the Brillouin zone. The procedure generates several thermo-physical properties of interest in materials science and geophysics (transverse and longitudinal wave velocities, shear modulus, Young modulus, Poisson ratio) all consistent with experimentally determined properties. A representative cluster is then abstracted from the cell and a detailed electron localization/delocalization analysis is performed on it, in the ground state geometry, and on deformed states imposed by two peculiar mixed asymmetric stretching/bending modes affecting the silicate chain that, according to literature data, have anomalous mode Grüneisen parameters. A Bader analysis reveals an intriguing feature associated with these deformations: an increase in the covalence of the Si-O bond that strengthens the linkage opposing the weakening induced by thermal stress. Finally, on the same cluster, the Ramsey contributions to the J NM coupling are evaluated by the gauge-independent atomic orbital method. The calculated isotropic chemical shifts of both 23 Na and 29 Si are again in substantial agreement with observations.
Genova, Alessandro; Ceresoli, Davide; Pavanello, Michele
2016-06-21
In this work we achieve three milestones: (1) we present a subsystem DFT method capable of running ab-initio molecular dynamics simulations accurately and efficiently. (2) In order to rid the simulations of inter-molecular self-interaction error, we exploit the ability of semilocal frozen density embedding formulation of subsystem DFT to represent the total electron density as a sum of localized subsystem electron densities that are constrained to integrate to a preset, constant number of electrons; the success of the method relies on the fact that employed semilocal nonadditive kinetic energy functionals effectively cancel out errors in semilocal exchange-correlation potentials that are linked to static correlation effects and self-interaction. (3) We demonstrate this concept by simulating liquid water and solvated OH(•) radical. While the bulk of our simulations have been performed on a periodic box containing 64 independent water molecules for 52 ps, we also simulated a box containing 256 water molecules for 22 ps. The results show that, provided one employs an accurate nonadditive kinetic energy functional, the dynamics of liquid water and OH(•) radical are in semiquantitative agreement with experimental results or higher-level electronic structure calculations. Our assessments are based upon comparisons of radial and angular distribution functions as well as the diffusion coefficient of the liquid.
International Nuclear Information System (INIS)
Genova, Alessandro; Pavanello, Michele; Ceresoli, Davide
2016-01-01
In this work we achieve three milestones: (1) we present a subsystem DFT method capable of running ab-initio molecular dynamics simulations accurately and efficiently. (2) In order to rid the simulations of inter-molecular self-interaction error, we exploit the ability of semilocal frozen density embedding formulation of subsystem DFT to represent the total electron density as a sum of localized subsystem electron densities that are constrained to integrate to a preset, constant number of electrons; the success of the method relies on the fact that employed semilocal nonadditive kinetic energy functionals effectively cancel out errors in semilocal exchange–correlation potentials that are linked to static correlation effects and self-interaction. (3) We demonstrate this concept by simulating liquid water and solvated OH • radical. While the bulk of our simulations have been performed on a periodic box containing 64 independent water molecules for 52 ps, we also simulated a box containing 256 water molecules for 22 ps. The results show that, provided one employs an accurate nonadditive kinetic energy functional, the dynamics of liquid water and OH • radical are in semiquantitative agreement with experimental results or higher-level electronic structure calculations. Our assessments are based upon comparisons of radial and angular distribution functions as well as the diffusion coefficient of the liquid.
Fang, CM; deGroot, RA; Wiegers, GA; Haas, C
1996-01-01
In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)(1.20)TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar
Fang, C.M.; Groot, R.A. de; Wiegers, G.A.; Haas, C.
1996-01-01
In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)1.20TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar
Unique electron transport in ultrathin black phosphorene: Ab-initio study
International Nuclear Information System (INIS)
Srivastava, Anurag; Khan, Md. Shahzad; Gupta, Sanjeev Kumar; Pandey, Ravindra
2015-01-01
Graphical abstract: Charge transfer configuration for NH 3 and NO 2 adsorbed 2D black-phospherene. - Highlights: • Ultrathin black phosphorene has been investigated, in terms of its optical and ballistic quantum transport properties. • The device performance subtaintially increases in armchair direction of black phosphorene. • Maximum reflectivity (43%) is observed at 1.85 eV (670 nm) and the reflective spectrum dispersed in visible range. • At low bias semiconducting and higher bias ohmic nature pointing black phospherene a promising material for high perfomrance device applications. • For NO 2 gas, this quasi 2D-black phosphorene surface shows strong affinity followed with substantial charge tranfer. - Abstract: We present first principle structural, electronic, optical and transport analysis of black phosphorene a 2D layered material. The studied configuration shows semiconducting nature and the states around the Fermi energy are mainly contributed by the p-orbitals of atoms. In optical properties, the reflective spectrum is approximately dispersed in visible range suggesting that this 2D-nanostructure can be considered as shielding for visible region. Due to the anisotropy of the electronic structure of black phosphorene, the device performance is subtaintially preferable in armchair direction. Zero-bias transmission shows no conductance channel near Fermi level but in far region prominent spectra for the same is observed for black-phospherene. The studied configurations show non-linear current–voltage (I–V) characteristics. The sensitivity for NH 3 and NO 2 gas molecule is explored using electronic and current–voltage (I–V) characteristics. Investigations show that the black phosphorene has strong affinity for electron seeking NO 2 molecule, thus providing an opportunity for its sensor application.
Unique electron transport in ultrathin black phosphorene: Ab-initio study
Energy Technology Data Exchange (ETDEWEB)
Srivastava, Anurag, E-mail: profanurag@gmail.com [Advanced Materials Research Group, Computational Nanoscience & Technology Lab, ABV-Indian Institute of Information Technology and Management, Gwalior (M.P.) 474010 India (India); Khan, Md. Shahzad [Advanced Materials Research Group, Computational Nanoscience & Technology Lab, ABV-Indian Institute of Information Technology and Management, Gwalior (M.P.) 474010 India (India); Gupta, Sanjeev Kumar [Department of Physics, St. Xavier' s College, Ahmedabad 380009 (India); Pandey, Ravindra [Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 (United States)
2015-11-30
Graphical abstract: Charge transfer configuration for NH{sub 3} and NO{sub 2} adsorbed 2D black-phospherene. - Highlights: • Ultrathin black phosphorene has been investigated, in terms of its optical and ballistic quantum transport properties. • The device performance subtaintially increases in armchair direction of black phosphorene. • Maximum reflectivity (43%) is observed at 1.85 eV (670 nm) and the reflective spectrum dispersed in visible range. • At low bias semiconducting and higher bias ohmic nature pointing black phospherene a promising material for high perfomrance device applications. • For NO{sub 2} gas, this quasi 2D-black phosphorene surface shows strong affinity followed with substantial charge tranfer. - Abstract: We present first principle structural, electronic, optical and transport analysis of black phosphorene a 2D layered material. The studied configuration shows semiconducting nature and the states around the Fermi energy are mainly contributed by the p-orbitals of atoms. In optical properties, the reflective spectrum is approximately dispersed in visible range suggesting that this 2D-nanostructure can be considered as shielding for visible region. Due to the anisotropy of the electronic structure of black phosphorene, the device performance is subtaintially preferable in armchair direction. Zero-bias transmission shows no conductance channel near Fermi level but in far region prominent spectra for the same is observed for black-phospherene. The studied configurations show non-linear current–voltage (I–V) characteristics. The sensitivity for NH{sub 3} and NO{sub 2} gas molecule is explored using electronic and current–voltage (I–V) characteristics. Investigations show that the black phosphorene has strong affinity for electron seeking NO{sub 2} molecule, thus providing an opportunity for its sensor application.
Structural insights and ab initio sequencing within the DING proteins family
International Nuclear Information System (INIS)
Elias, Mikael; Liebschner, Dorothee; Gotthard, Guillaume; Chabriere, Eric
2011-01-01
DING proteins constitute a recently discovered protein family that is ubiquitous in eukaryotes. The structural insights and the physiological involvements of these intriguing proteins are hereby deciphered. DING proteins constitute an intriguing family of phosphate-binding proteins that was identified in a wide range of organisms, from prokaryotes and archae to eukaryotes. Despite their seemingly ubiquitous occurrence in eukaryotes, their encoding genes are missing from sequenced genomes. Such a lack has considerably hampered functional studies. In humans, these proteins have been related to several diseases, like atherosclerosis, kidney stones, inflammation processes and HIV inhibition. The human phosphate binding protein is a human representative of the DING family that was serendipitously discovered from human plasma. An original approach was developed to determine ab initio the complete and exact sequence of this 38 kDa protein by utilizing mass spectrometry and X-ray data in tandem. Taking advantage of this first complete eukaryotic DING sequence, a immunohistochemistry study was undertaken to check the presence of DING proteins in various mice tissues, revealing that these proteins are widely expressed. Finally, the structure of a bacterial representative from Pseudomonas fluorescens was solved at sub-angstrom resolution, allowing the molecular mechanism of the phosphate binding in these high-affinity proteins to be elucidated
Structural insights and ab initio sequencing within the DING proteins family
Energy Technology Data Exchange (ETDEWEB)
Elias, Mikael, E-mail: mikael.elias@weizmann.ac.il [Weizmann Institute of Science, Rehovot (Israel); Liebschner, Dorothee [CRM2, Nancy Université (France); Gotthard, Guillaume; Chabriere, Eric [AFMB, Université Aix-Marseille II (France)
2011-01-01
DING proteins constitute a recently discovered protein family that is ubiquitous in eukaryotes. The structural insights and the physiological involvements of these intriguing proteins are hereby deciphered. DING proteins constitute an intriguing family of phosphate-binding proteins that was identified in a wide range of organisms, from prokaryotes and archae to eukaryotes. Despite their seemingly ubiquitous occurrence in eukaryotes, their encoding genes are missing from sequenced genomes. Such a lack has considerably hampered functional studies. In humans, these proteins have been related to several diseases, like atherosclerosis, kidney stones, inflammation processes and HIV inhibition. The human phosphate binding protein is a human representative of the DING family that was serendipitously discovered from human plasma. An original approach was developed to determine ab initio the complete and exact sequence of this 38 kDa protein by utilizing mass spectrometry and X-ray data in tandem. Taking advantage of this first complete eukaryotic DING sequence, a immunohistochemistry study was undertaken to check the presence of DING proteins in various mice tissues, revealing that these proteins are widely expressed. Finally, the structure of a bacterial representative from Pseudomonas fluorescens was solved at sub-angstrom resolution, allowing the molecular mechanism of the phosphate binding in these high-affinity proteins to be elucidated.
A Deep Learning Network Approach to ab initio Protein Secondary Structure Prediction.
Spencer, Matt; Eickholt, Jesse; Jianlin Cheng
2015-01-01
Ab initio protein secondary structure (SS) predictions are utilized to generate tertiary structure predictions, which are increasingly demanded due to the rapid discovery of proteins. Although recent developments have slightly exceeded previous methods of SS prediction, accuracy has stagnated around 80 percent and many wonder if prediction cannot be advanced beyond this ceiling. Disciplines that have traditionally employed neural networks are experimenting with novel deep learning techniques in attempts to stimulate progress. Since neural networks have historically played an important role in SS prediction, we wanted to determine whether deep learning could contribute to the advancement of this field as well. We developed an SS predictor that makes use of the position-specific scoring matrix generated by PSI-BLAST and deep learning network architectures, which we call DNSS. Graphical processing units and CUDA software optimize the deep network architecture and efficiently train the deep networks. Optimal parameters for the training process were determined, and a workflow comprising three separately trained deep networks was constructed in order to make refined predictions. This deep learning network approach was used to predict SS for a fully independent test dataset of 198 proteins, achieving a Q3 accuracy of 80.7 percent and a Sov accuracy of 74.2 percent.
Ab initio structure determination and refinement of a scorpion protein toxin.
Smith, G D; Blessing, R H; Ealick, S E; Fontecilla-Camps, J C; Hauptman, H A; Housset, D; Langs, D A; Miller, R
1997-09-01
The structure of toxin II from the scorpion Androctonus australis Hector has been determined ab initio by direct methods using SnB at 0.96 A resolution. For the purpose of this structure redetermination, undertaken as a test of the minimal function and the SnB program, the identity and sequence of the protein was withheld from part of the research team. A single solution obtained from 1 619 random atom trials was clearly revealed by the bimodal distribution of the final value of the minimal function associated with each individual trial. Five peptide fragments were identified from a conservative analysis of the initial E-map, and following several refinement cycles with X-PLOR, a model was built of the complete structure. At the end of the X-PLOR refinement, the sequence was compared with the published sequence and 57 of the 64 residues had been correctly identified. Two errors in sequence resulted from side chains with similar size while the rest of the errors were a result of severe disorder or high thermal motion in the side chains. Given the amino-acid sequence, it is estimated that the initial E-map could have produced a model containing 99% of all main-chain and 81% of side-chain atoms. The structure refinement was completed with PROFFT, including the contributions of protein H atoms, and converged at a residual of 0.158 for 30 609 data with F >or= 2sigma(F) in the resolution range 8.0-0.964 A. The final model consisted of 518 non-H protein atoms (36 disordered), 407 H atoms, and 129 water molecules (43 with occupancies less than unity). This total of 647 non-H atoms represents the largest light-atom structure solved to date.
Modern quantum chemistry introduction to advanced electronic structure theory
Szabo, Attila
1996-01-01
The aim of this graduate-level textbook is to present and explain, at other than a superficial level, modem ab initio approaches to the calculation of the electronic structure and properties of molecules. The first three chapters contain introductory material culminating in a thorough discussion of the Hartree-Fock approximation.The remaining four chapters describe a variety of more sophisticated approaches, which improve upon this approximation.Among the highlights of the seven chapters are (1) a review of the mathematics (mostly matrix algebra) required for the rest of the book, (2) an intr
Ferreira da Silva, F.; Lange, E.; Limão-Vieira, P.; Jones, N. C.; Hoffmann, S. V.; Hubin-Franskin, M.-J.; Delwiche, J.; Brunger, M. J.; Neves, R. F. C.; Lopes, M. C. A.; de Oliveira, E. M.; da Costa, R. F.; Varella, M. T. do N.; Bettega, M. H. F.; Blanco, F.; García, G.; Lima, M. A. P.; Jones, D. B.
2015-10-01
The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5-10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.
International Nuclear Information System (INIS)
Ferreira da Silva, F.; Lange, E.; Limão-Vieira, P.; Jones, N. C.; Hoffmann, S. V.; Hubin-Franskin, M.-J.; Delwiche, J.; Brunger, M. J.
2015-01-01
The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5–10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range
Energy Technology Data Exchange (ETDEWEB)
Ferreira da Silva, F.; Lange, E. [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt, E-mail: michael.brunger@flinders.edu.au, E-mail: maplima@ifi.unicamp.br [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Jones, N. C.; Hoffmann, S. V. [ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Århus C (Denmark); Hubin-Franskin, M.-J.; Delwiche, J. [Départment de Chimie, Institut de Chimie-Bât. B6C, Université de Liège, B-4000 Liège 1 (Belgium); Brunger, M. J., E-mail: plimaovieira@fct.unl.pt, E-mail: michael.brunger@flinders.edu.au, E-mail: maplima@ifi.unicamp.br [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); and others
2015-10-14
The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5–10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.
International Nuclear Information System (INIS)
Sobolewski, Andrzej L.; Domcke, Wolfgang
2003-01-01
The low-lying 1 ππ* excited states of the 2-aminopyridine dimer have been investigated with multi-reference ab initio methods (CASSCF and MRMP2). The 2-aminopyridine dimer can be considered as a mimetic model of Watson-Crick DNA base pairs. The reaction path and the energy profile for single proton transfer in the lowest 1 ππ* inter-monomer charge-transfer state have been obtained. A weakly avoided crossing of the 1 ππ* surface with the electronic ground-state surface has been found near the single-proton-transfer minimum of the 1 ππ* surface. From the splitting of the adiabatic surfaces at the avoided crossing, an internal-conversion lifetime of the excited state of <100 ps has been estimated. The potential relevance of these results for the rationalization of radiation-induced mutations and the photostability of the genetic code is briefly discussed
International Nuclear Information System (INIS)
Hicks, Latorya D.; Fry, Albert J.; Kurzweil, Vanessa C.
2004-01-01
The electron affinities (EAs) of a training set of 29 monosubstituted benzalacetophenones (chalcones) were computed at the ab initio density functional B3LYP/6-31G * level of theory. The EAs and experimental reduction potentials of the training set are highly linearly correlated (correlation coefficient of 0.969 and standard deviation of 10.8 mV). An additional 72 di-, tri-, and tetrasubstituted chalcones were then synthesized. Their reduction potentials were predicted from computed EAs using the linear correlation derived from the training set. Agreement between the experimental and computed reduction potentials is remarkably good, with a standard deviation of less than 22 mV for this very large set of substances whose potentials extend over a range of almost 700 mV
Pressure induced structural phase transition in SnS—An ab initio study
Indian Academy of Sciences (India)
Unknown
Abstract. The structural behaviour of SnS under pressure has been investigated by first principle density functional ... tural phase transition from orthorhombic type to monoclinic type structure around 17 GPa which is in good agreement with the ... is achieved by performing the electronic structure and total energy calculation ...
Varadwaj, Pradeep Risikrishna
2010-05-01
Spin-restricted DFT (X3LYP and B3LYP) and ab initio (MP2(fc) and CCSD(fc)) calculations in conjunction with the Aug-CC-pVDZ and Aug-CC-pVTZ basis sets were performed on a series of hydrogen bonded complexes PN...HX (X = F, Cl, Br) to examine the variations of their equilibrium gas phase structures, energetic stabilities, electronic properties, and vibrational characteristics in their electronic ground states. In all cases the complexes were predicted to be stable with respect to the constituent monomers. The interaction energy (Delta E) calculated using a super-molecular model is found to be in this order: PN...HF > PN...HCl > PN...HBr in the series examined. Analysis of various physically meaningful contributions arising from the Kitaura-Morokuma (KM) and reduced variational space self-consistent-field (RVS-SCF) energy decomposition procedures shows that the electrostatic energy has significant contribution to the over-all interaction energy. Dipole moment enhancement (Delta mu) was observed in these complexes expected of predominant dipole-dipole electrostatic interaction and was found to follow the trend PN...HF > PN...HCl > PN...HBr at the CCSD level. However, the DFT (X3LYP and B3LYP) and MP2 levels less accurately determined these values (in this order HF 0, nabla(2)rho(c) > 0 and H(c) > 0 at the BCP) whilst the bonds in PN (rho(c) > 0, nabla(2)rho(c) > 0 and H(c) 0, nabla(2)rho(c) BD*(HX) delocalization.
Hao, Xiaohu; Zhang, Guijun; Zhou, Xiaogen
2018-04-01
Computing conformations which are essential to associate structural and functional information with gene sequences, is challenging due to the high dimensionality and rugged energy surface of the protein conformational space. Consequently, the dimension of the protein conformational space should be reduced to a proper level, and an effective exploring algorithm should be proposed. In this paper, a plug-in method for guiding exploration in conformational feature space with Lipschitz underestimation (LUE) for ab-initio protein structure prediction is proposed. The conformational space is converted into ultrafast shape recognition (USR) feature space firstly. Based on the USR feature space, the conformational space can be further converted into Underestimation space according to Lipschitz estimation theory for guiding exploration. As a consequence of the use of underestimation model, the tight lower bound estimate information can be used for exploration guidance, the invalid sampling areas can be eliminated in advance, and the number of energy function evaluations can be reduced. The proposed method provides a novel technique to solve the exploring problem of protein conformational space. LUE is applied to differential evolution (DE) algorithm, and metropolis Monte Carlo(MMC) algorithm which is available in the Rosetta; When LUE is applied to DE and MMC, it will be screened by the underestimation method prior to energy calculation and selection. Further, LUE is compared with DE and MMC by testing on 15 small-to-medium structurally diverse proteins. Test results show that near-native protein structures with higher accuracy can be obtained more rapidly and efficiently with the use of LUE. Copyright © 2018 Elsevier Ltd. All rights reserved.
In-medium no-core shell model for ab initio nuclear structure calculations
International Nuclear Information System (INIS)
Gebrerufael, Eskendr
2017-01-01
In this work, we merge two successful ab initio nuclear-structure methods, the no-core shell model (NCSM) and the multi-reference in-medium similarity renormalization group (IM-SRG), to define a novel many-body approach for the comprehensive description of ground and excited states of closed- and open-shell medium-mass nuclei. Building on the key advantages of the two methods - the decoupling of excitations at the many-body level in the IM-SRG, and the exact diagonalization in the NCSM applicable up to medium-light nuclei - their combination enables fully converged no-core calculations for an unprecedented range of nuclei and observables at moderate computational cost. The efficiency and rapid model-space convergence of the new approach make it ideally suited for ab initio studies of ground and low-lying excited states of nuclei up to the medium-mass regime. Interactions constructed within the framework of chiral effective field theory provide an excellent opportunity to describe properties of nuclei from first principles, i.e., rooted in quantum chromodynamics, they overcome the lack of predictive power of phenomenological potentials. The hard core of these interactions causes strong short-range correlations, which we soften by using the similarity-renormalization-group transformation that accelerates the model-space convergence of many-body calculations. Three-nucleon effects, which are mandatory for the correct description of bulk properties of nuclei, are included in our calculations by using the normal-ordered two-body approximation, which has been shown to be sufficient to capture the main effects of the three-nucleon interaction. Using these interactions, we analyze energies of ground and excited states in the carbon and oxygen isotopic chains, where conventional NCSM calculations are still feasible and provide an important benchmark. Furthermore, we study the Hoyle state in 12 C - a three-alpha cluster state that cannot be converged in standard NCSM
Ab initio valence calculations in chemistry
Cook, D B
1974-01-01
Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge
Gorai, S.; Ghosh, P. S.; Bhattacharya, C.; Arya, A.
2018-04-01
The pressure evolution of phase stability, structural and mechanical properties of Fe3C in ferro-magnetic (FM) and high pressure non magnetic (NM) phase is investigated from first principle calculations. The 2nd order FM to NM phase transition of Fe3C is identified around 60 GPa. Pressure (or density) variation of sound velocities from our ab-initio calculated single crystal elastic constants are determined to predict these parameters at Earth's outer core pressure.
Electronic structure of superlattices
International Nuclear Information System (INIS)
Altarelli, M.
1987-01-01
Calculations of electronic states in semiconductor superlattices are briefly reviewed, with emphasis on the envelope-function method and on comparison with experiments. The energy levels in presence of external magnetic fields are discussed and compared to magneto-optical experiments. (author) [pt
International Nuclear Information System (INIS)
Monteseguro, V.; Rodríguez-Hernández, P.; Muñoz, A.
2015-01-01
The structural, elastic, and vibrational properties of yttrium aluminum garnet Y 3 Al 5 O 12 are studied under high pressure by ab initio calculations in the framework of the density functional theory. The calculated ground state properties are in good agreement with the available experimental data. Pressure dependences of bond length and bulk moduli of the constituent polyhedra are reported. The evolution of the elastic constants and the major elastic properties, Young and shear modulus, Poisson's ratios, and Zener anisotropy ratio, are described. The mechanical stability is analyzed, on the light of “Born generalized stability criteria,” showing that the garnet is mechanically unstable above 116 GPa. Symmetries, frequencies, and pressure coefficients of the Raman-active modes are discussed on the basis of the calculated total and partial phonon density of states, which reflect the dynamical contribution of each atom. The relations between the phonon modes of Y 3 Al 5 O 12 and the internal and external molecular modes of the different polyhedra are discussed. Infrared-active modes, as well as the silent modes, and their pressure dependence are also investigated. No dynamical instabilities were found below 116 GPa
Energy Technology Data Exchange (ETDEWEB)
Saalfrank, Peter [Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam (Germany); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Juaristi, J. I. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20018 Donostia-San Sebastián (Spain); Alducin, M.; Muiño, R. Díez [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Blanco-Rey, M. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20018 Donostia-San Sebastián (Spain)
2014-12-21
Using density functional theory and Ab Initio Molecular Dynamics with Electronic Friction (AIMDEF), we study the adsorption and dissipative vibrational dynamics of hydrogen atoms chemisorbed on free-standing lead films of increasing thickness. Lead films are known for their oscillatory behaviour of certain properties with increasing thickness, e.g., energy and electron spillout change in discontinuous manner, due to quantum size effects [G. Materzanini, P. Saalfrank, and P. J. D. Lindan, Phys. Rev. B 63, 235405 (2001)]. Here, we demonstrate that oscillatory features arise also for hydrogen when chemisorbed on lead films. Besides stationary properties of the adsorbate, we concentrate on finite vibrational lifetimes of H-surface vibrations. As shown by AIMDEF, the damping via vibration-electron hole pair coupling dominates clearly over the vibration-phonon channel, in particular for high-frequency modes. Vibrational relaxation times are a characteristic function of layer thickness due to the oscillating behaviour of the embedding surface electronic density. Implications derived from AIMDEF for frictional many-atom dynamics, and physisorbed species will also be given.
Energy Technology Data Exchange (ETDEWEB)
Gharabaghi, Masumeh [Faculty of Chemical and Petroleum Sciences, Shahid Beheshti University, G. C., Evin, Tehran, 19839, P.O. Box 19395-4716 (Iran, Islamic Republic of); Shahbazian, Shant, E-mail: chemist_shant@yahoo.com [Department of Physics, Shahid Beheshti University, G. C., Evin, Tehran, 19839, P.O. Box 19395-4716 (Iran, Islamic Republic of)
2016-12-09
In this letter the conceptual and computational implications of the Hartree product type nuclear wavefunction introduced recently within the context of the ab initio non-Born–Oppenheimer Nuclear–electronic orbital (NEO) methodology are considered. It is demonstrated that this wavefunction may imply a pseudo-adiabatic separation of the nuclei and electrons and each nucleus is conceived as a quantum oscillator while a non-Coulombic effective Hamiltonian is deduced for electrons. Using the variational principle this Hamiltonian is employed to derive a modified set of single-component Hartree–Fock equations which are equivalent to the multi-component version derived previously within the context of the NEO and, easy to be implemented computationally. - Highlights: • The Hartree product wavefunction is used for the quantum nuclei of a molecule. • With this wavefunction quantum nuclei may be conceived as quantum oscillators. • Using variational integral, non-Coulomb effective electronic Hamiltonian was derived. • A set of modified Hartree–Fock equations were derived from this Hamiltonian. • The derived equations are equivalent to the multi-component Hartree–Fock equations.
Single-layer 1T‧-MoS2 under electron irradiation from ab initio molecular dynamics
Pizzochero, Michele; Yazyev, Oleg V.
2018-04-01
Irradiation with high-energy particles has recently emerged as an effective tool for tailoring the properties of two-dimensional transition metal dichalcogenides. In order to carry out an atomically-precise manipulation of the lattice, a detailed understanding of the beam-induced events occurring at the atomic scale is necessary. Here, we investigate the response of 1T' -MoS2 to the electron irradiation by ab initio molecular dynamics means. Our simulations suggest that an electron beam with energy smaller than 75 keV does not result in any knock-on damage. The displacement threshold energies are different for the two nonequivalent sulfur atoms in 1T' -MoS2 and strongly depend on whether the top or bottom chalcogen layer is considered. As a result, a careful tuning of the beam energy can promote the formation of ordered defects in the sample. We further discuss the effect of the electron irradiation in the neighborhood of a defective site, the mobility of the sulfur vacancies created and their tendency to aggregate. Overall, our work provides useful guidelines for the imaging and the defect engineering of 1T' -MoS2 using electron microscopy.
International Nuclear Information System (INIS)
Saha, H.P.
1993-01-01
The multiconfiguration Hartree-Fock method for continuum wave functions has been used to calculate the scattering length and phase shifts over extremely low energies ranging from 0 to 1 eV very accurately for electron-helium scattering. The scattering length is calculated very accurately with wave functions computed exactly at zero energy, resulting in an upper bound of 1.1784. The electron correlation and polarization of the target by the scattering electron, which are very important in these calculations, have been taken into account in an accurate ab initio manner through the configuration-interaction procedure by optimizing both bound and continuum orbitals simultaneously at each kinetic energy of the scattered electron. Detailed results for scattering length, differential, total, and momentum-transfer cross sections obtained from the phase shifts are presented. The present scattering length is found to be in excellent agreement with the experimental result of Andrick and Bitsch [J. Phys. B 8, 402 (1975)] and the theoretical result of O'Malley, Burke, and Berrington [J. Phys. B 12, 953 (1979)]. There is excellent agreement between the present total cross sections and the corresponding experimental measurements of Buckman and Lohmann [J. Phys. B 19, 2547 (1986)]. The present momentum-transfer cross sections also show remarkable agreement with the experimental results of Crompton, Elford, and Robertson [Aust. J. Phys. 23, 667 (1970)
Moghram, Basem Ameen; Nabil, Emad; Badr, Amr
2018-01-01
T-cell epitope structure identification is a significant challenging immunoinformatic problem within epitope-based vaccine design. Epitopes or antigenic peptides are a set of amino acids that bind with the Major Histocompatibility Complex (MHC) molecules. The aim of this process is presented by Antigen Presenting Cells to be inspected by T-cells. MHC-molecule-binding epitopes are responsible for triggering the immune response to antigens. The epitope's three-dimensional (3D) molecular structure (i.e., tertiary structure) reflects its proper function. Therefore, the identification of MHC class-II epitopes structure is a significant step towards epitope-based vaccine design and understanding of the immune system. In this paper, we propose a new technique using a Genetic Algorithm for Predicting the Epitope Structure (GAPES), to predict the structure of MHC class-II epitopes based on their sequence. The proposed Elitist-based genetic algorithm for predicting the epitope's tertiary structure is based on Ab-Initio Empirical Conformational Energy Program for Peptides (ECEPP) Force Field Model. The developed secondary structure prediction technique relies on Ramachandran Plot. We used two alignment algorithms: the ROSS alignment and TM-Score alignment. We applied four different alignment approaches to calculate the similarity scores of the dataset under test. We utilized the support vector machine (SVM) classifier as an evaluation of the prediction performance. The prediction accuracy and the Area Under Receiver Operating Characteristic (ROC) Curve (AUC) were calculated as measures of performance. The calculations are performed on twelve similarity-reduced datasets of the Immune Epitope Data Base (IEDB) and a large dataset of peptide-binding affinities to HLA-DRB1*0101. The results showed that GAPES was reliable and very accurate. We achieved an average prediction accuracy of 93.50% and an average AUC of 0.974 in the IEDB dataset. Also, we achieved an accuracy of 95
Electronic structure of alloys
International Nuclear Information System (INIS)
Ehrenreich, H.; Schwartz, L.M.
1976-01-01
The description of electronic properties of binary substitutional alloys within the single particle approximation is reviewed. Emphasis is placed on a didactic exposition of the equilibrium properties of the transport and magnetic properties of such alloys. Topics covered include: multiple scattering theory; the single band alloy; formal extensions of the theory; the alloy potential; realistic model state densities; the s-d model; and the muffin tin model. 43 figures, 3 tables, 151 references
Nugraha, T. A.; Rohrmueller, M.; Gerstmann, U.; Greulich-Weber, S.; Stellhorn, A.; Cantin, J. L.; von Bardeleben, J.; Schmidt, W. G.; Wippermann, S.
SiC is widely used in high-power, high-frequency electronic devices. Recently, it has also been employed as a building block in nanocomposites used as light absorbers in solar energy conversion devices. Analogous to Si, SiC features SiO2 as native oxide that can be used for passivation and insulating layers. However, a significant number of defect states are reported to form at SiC/SiO2 interfaces, limiting mobility and increasing recombination of free charge carriers. We investigated the growth of oxide on different 3C-SiC surfaces from first principles. Carbon antisite Csi defects are found to be strongly stabilized in particular at the interface, because carbon changes its hybridization from sp3 in the SiC-bulk to sp2 at the interface, creating a dangling bond inside a porous region of the SiO2 passivating layer. Combining ab initio g-tensor calculations and electron paramagnetic resonance (EPR) measurements, we show that Csi defects explain the measured EPR signatures, while the hyperfine structure allows to obtain local structural information of the oxide layer. Financial support from BMBF NanoMatFutur Grant 13N12972 and DFG priority program SPP-1601 is gratefully acknowledged.
International Nuclear Information System (INIS)
Caravaca, M A; Casali, R A
2005-01-01
The SIESTA approach based on pseudopotentials and a localized basis set is used to calculate the electronic, elastic and equilibrium properties of P 2 1 /c, Pbca, Pnma, Fm3m, P4 2 nmc and Pa3 phases of HfO 2 . Using separable Troullier-Martins norm-conserving pseudopotentials which include partial core corrections for Hf, we tested important physical properties as a function of the basis set size, grid size and cut-off ratio of the pseudo-atomic orbitals (PAOs). We found that calculations in this oxide with the LDA approach and using a minimal basis set (simple zeta, SZ) improve calculated phase transition pressures with respect to the double-zeta basis set and LDA (DZ-LDA), and show similar accuracy to that determined with the PPPW and GGA approach. Still, the equilibrium volumes and structural properties calculated with SZ-LDA compare better with experiments than the GGA approach. The bandgaps and elastic and structural properties calculated with DZ-LDA are accurate in agreement with previous state of the art ab initio calculations and experimental evidence and cannot be improved with a polarized basis set. These calculated properties show low sensitivity to the PAO localization parameter range between 40 and 100 meV. However, this is not true for the relative energy, which improves upon decrease of the mentioned parameter. We found a non-linear behaviour in the lattice parameters with pressure in the P 2 1 /c phase, showing a discontinuity of the derivative of the a lattice parameter with respect to external pressure, as found in experiments. The common enthalpy values calculated with the minimal basis set give pressure transitions of 3.3 and 10.8?GPa for P2 1 /c → Pbca and Pbca → Pnma, respectively, in accordance with different high pressure experimental values
Energy Technology Data Exchange (ETDEWEB)
Caravaca, M A [Facultad de Ingenieria, Universidad Nacional del Nordeste, Avenida Las Heras 727, 3500-Resistencia (Argentina); Casali, R A [Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste, Avenida Libertad, 5600-Corrientes (Argentina)
2005-09-21
The SIESTA approach based on pseudopotentials and a localized basis set is used to calculate the electronic, elastic and equilibrium properties of P 2{sub 1}/c, Pbca, Pnma, Fm3m, P4{sub 2}nmc and Pa3 phases of HfO{sub 2}. Using separable Troullier-Martins norm-conserving pseudopotentials which include partial core corrections for Hf, we tested important physical properties as a function of the basis set size, grid size and cut-off ratio of the pseudo-atomic orbitals (PAOs). We found that calculations in this oxide with the LDA approach and using a minimal basis set (simple zeta, SZ) improve calculated phase transition pressures with respect to the double-zeta basis set and LDA (DZ-LDA), and show similar accuracy to that determined with the PPPW and GGA approach. Still, the equilibrium volumes and structural properties calculated with SZ-LDA compare better with experiments than the GGA approach. The bandgaps and elastic and structural properties calculated with DZ-LDA are accurate in agreement with previous state of the art ab initio calculations and experimental evidence and cannot be improved with a polarized basis set. These calculated properties show low sensitivity to the PAO localization parameter range between 40 and 100 meV. However, this is not true for the relative energy, which improves upon decrease of the mentioned parameter. We found a non-linear behaviour in the lattice parameters with pressure in the P 2{sub 1}/c phase, showing a discontinuity of the derivative of the a lattice parameter with respect to external pressure, as found in experiments. The common enthalpy values calculated with the minimal basis set give pressure transitions of 3.3 and 10.8?GPa for P2{sub 1}/c {yields} Pbca and Pbca {yields} Pnma, respectively, in accordance with different high pressure experimental values.
Electronic transport properties of nano-scale Si films: an ab initio study
Maassen, Jesse; Ke, Youqi; Zahid, Ferdows; Guo, Hong
2010-03-01
Using a recently developed first principles transport package, we study the electronic transport properties of Si films contacted to heavily doped n-type Si leads. The quantum transport analysis is carried out using density functional theory (DFT) combined with nonequilibrium Green's functions (NEGF). This particular combination of NEGF-DFT allows the investigation of Si films with thicknesses in the range of a few nanometers and lengths up to tens of nanometers. We calculate the conductance, the momentum resolved transmission, the potential profile and the screening length as a function of length, thickness, orientation and surface structure. Moreover, we compare the properties of Si films with and without a top surface passivation by hydrogen.
Electronics for Piezoelectric Smart Structures
Warkentin, D. J.; Tani, J.
1997-01-01
This paper briefly presents work addressing some of the basic considerations for the electronic components used in smart structures incorporating piezoelectric elements. After general remarks on the application of piezoelectric elements to the problem of structural vibration control, three main topics are described. Work to date on the development of techniques for embedding electronic components within structural parts is presented, followed by a description of the power flow and dissipation requirements of those components. Finally current work on the development of electronic circuits for use in an 'active wall' for acoustic noise is introduced.
Fang, CM; Wiegers, GA; Haas, C; deGroot, RA
1997-01-01
The transition-metal dichalcogenides ReX2 (X = Sor Se) and TcS2 with a d(3) electron configuration have distorted; CdCl2 and Cd(OH)(2) structures, respectively, with the Re(Tc) atoms in each layer forming parallelogram-shaped connected clusters (diamond chain). Ab-initio band-structure calculations
LDA+U and tight-binding electronic structure of InN nanowires
Molina-Sánchez, A.; García-Cristóbal, A.; Cantarero, A.; Terentjevs, A.; Cicero, G.
2010-10-01
In this paper we employ a combined ab initio and tight-binding approach to obtain the electronic and optical properties of hydrogenated Indium nitride (InN) nanowires. We first discuss InN band structure for the wurtzite structure calculated at the LDA+U level and use this information to extract the parameters needed for an empirical tight-binging implementation. These parameters are then employed to calculate the electronic and optical properties of InN nanowires in a diameter range that would not be affordable by ab initio techniques. The reliability of the large nanowires results is assessed by explicitly comparing the electronic structure of a small diameter wire studied both at LDA+U and tight-binding level.
Input/Output of ab-initio nuclear structure calculations for improved performance and portability
International Nuclear Information System (INIS)
Laghave, Nikhil
2010-01-01
Many modern scientific applications rely on highly computation intensive calculations. However, most applications do not concentrate as much on the role that input/output operations can play for improved performance and portability. Parallelizing input/output operations of large files can significantly improve the performance of parallel applications where sequential I/O is a bottleneck. A proper choice of I/O library also offers a scope for making input/output operations portable across different architectures. Thus, use of parallel I/O libraries for organizing I/O of large data files offers great scope in improving performance and portability of applications. In particular, sequential I/O has been identified as a bottleneck for the highly scalable MFDn (Many Fermion Dynamics for nuclear structure) code performing ab-initio nuclear structure calculations. We develop interfaces and parallel I/O procedures to use a well-known parallel I/O library in MFDn. As a result, we gain efficient I/O of large datasets along with their portability and ease of use in the down-stream processing. Even situations where the amount of data to be written is not huge, proper use of input/output operations can boost the performance of scientific applications. Application checkpointing offers enormous performance improvement and flexibility by doing a negligible amount of I/O to disk. Checkpointing saves and resumes application state in such a manner that in most cases the application is unaware that there has been an interruption to its execution. This helps in saving large amount of work that has been previously done and continue application execution. This small amount of I/O provides substantial time saving by offering restart/resume capability to applications. The need for checkpointing in optimization code NEWUOA has been identified and checkpoint/restart capability has been implemented in NEWUOA by using simple file I/O.
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, BP. 63, 46000 Safi (Morocco); LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble Cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Mounkachi, O.; El Moussaoui, H. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco)
2014-06-01
Self-consistent ab initio calculations, based on DFT (Density Functional Theory) approach and using FLAPW (Full potential Linear Augmented Plane Wave) method, are performed to investigate both electronic and magnetic properties of the MnSe lattice. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Mn lattices. Magnetic moments considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The zero-field high temperature static susceptibility series of the spin −4.28 nearest-neighbor Ising model on face centered cubic (fcc) and lattices is thoroughly analyzed by means of a power series coherent anomaly method (CAM). The exchange interaction between the magnetic atoms and the Néel temperature are deduced using the mean filed and HTSEs theories. - Highlights: • Ab initio calculations are used to investigate both electronic and magnetic properties of the MnSe alloys. • Obtained data from ab initio calculations are used as input for the HTSEs. • The Néel temperature is obtained for MnSe alloys.
Origin of the Hadži ABC structure: An ab initio study
Energy Technology Data Exchange (ETDEWEB)
Van Hoozen, Brian L.; Petersen, Poul B. [Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853 (United States)
2015-11-14
Medium and strong hydrogen bonds are well known to give rise to broad features in the vibrational spectrum often spanning several hundred wavenumbers. In some cases, these features can span over 1000 cm{sup −1} and even contain multiple broad peaks. One class of strongly hydrogen-bonded dimers that includes many different phosphinic, phosphoric, sulfinic, and selenic acid homodimers exhibits a three-peaked structure over 1500 cm{sup −1} broad. This unusual feature is often referred to as the Hadži ABC structure. The origin of this feature has been debated since its discovery in the 1950s. Only a couple of theoretical studies have attempted to interpret the origin of this feature; however, no previous study has been able to reproduce this feature from first principles. Here, we present the first ab initio calculation of the Hadži ABC structure. Using a reduced dimensionality calculation that includes four vibrational modes, we are able to reproduce the three-peak structure and much of the broadness of the feature. Our results indicate that Fermi resonances of the in-plane bend, out-of-plane bend, and combination of these bends play significant roles in explaining this feature. Much of the broadness of the feature and the ability of the OH stretch mode to couple with many overtone bending modes are captured by including an adiabatically separated dimer stretch mode in the model. This mode modulates the distance between the monomer units and accordingly the strength of the hydrogen-bonds causing the OH stretch frequency to shift from 2000 to 3000 cm{sup −1}. Using this model, we were also able to reproduce the vibrational spectrum of the deuterated isotopologue which consists of a single 500 cm{sup −1} broad feature. Whereas previous empirical studies have asserted that Fermi resonances contribute very little to this feature, our study indicates that while not appearing as a separate peak, a Fermi resonance of the in-plane bend contributes substantially to
Mikaeilzadeh, L.; Pirgholi, M.; Tavana, A.
2018-05-01
Based on the ab-initio non-equilibrium Green's function (NEGF) formalism based on the density functional theory (DFT), we have studied the electron transport in the all-Heusler device Co2CrSi/Cu2CrAl/Co2CrSi. Results show that the calculated transmission spectra is very sensitive to the structural parameters and the interface. Also, we obtain a range for the thickness of the spacer layer for which the MR effect is optimum. Calculations also show a perfect GMR effect in this device.
International Nuclear Information System (INIS)
Xiao, H.Y.; Gao, Fei; Zu, X.T.; Weber, W.J.
2010-01-01
High-pressure induced zinc blende to rocksalt phase transition in GaN has been investigated by ab initio molecular dynamics method to characterize the transformation mechanism at the atomic level. It was shown that at 100 GPa GaN passes through tetragonal and monoclinic states before rocksalt structure is formed. The transformation mechanism is consistent with that for other zinc blende semiconductors obtained from the same method. Detailed structural analysis showed that there is no bond breaking involved in the phase transition.
Energy Technology Data Exchange (ETDEWEB)
Grimminger, Robert; Clouthier, Dennis J., E-mail: dclaser@uky.edu [Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 (United States); Sheridan, Phillip M. [Department of Chemistry and Biochemistry, Canisius College, Buffalo, New York 14208 (United States)
2014-04-28
We have studied the B{sup ~} {sup 2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} laser-induced fluorescence (LIF) spectrum of the jet-cooled F{sub 2}BO radical for the first time. The transition consists of a strong 0{sub 0}{sup 0} band at 446.5 nm and eight weak sequence bands to shorter wavelengths. Single vibronic level emission spectra obtained by laser excitation of individual levels of the B{sup ~} state exhibit two electronic transitions: a very weak, sparse B{sup ~}–X{sup ~} band system in the 450–500 nm region and a stronger, more extensive set of B{sup ~} {sup 2}A{sub 1}–A{sup ~} {sup 2}B{sub 1} bands in the 580–650 nm region. We have also performed a series of high level ab initio calculations to predict the electronic energies, molecular structures, vibrational frequencies, and rotational and spin-rotation constants in the X{sup ~} {sup 2}B{sub 2}, A{sup ~2}B{sub 1} and B{sup ~} {sup 2}A{sub 1} electronic states as an aid to the analysis of the experimental data. The theoretical results have been used as input for simulations of the rotationally resolved B{sup ~} {sup 2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} 0{sub 0}{sup 0} LIF band and Franck-Condon profiles of the LIF and single vibronic level emission spectra. The agreement between the simulations obtained with purely ab initio parameters and the experimental spectra validates the geometries calculated for the ground and excited states and the conclusion that the radical has C{sub 2v} symmetry in the X{sup ~}, A{sup ~}, and B{sup ~} states. The spectra provide considerable new information about the vibrational energy levels of the X{sup ~} and A{sup ~} states, but very little for the B{sup ~} state, due to the very restrictive Franck-Condon factors in the LIF spectra.
Direct electron crystallographic determination of zeolite zonal structures
International Nuclear Information System (INIS)
Dorset, Douglas L.; Gilmore, Christopher J.; Jorda, Jose Luis; Nicolopoulos, Stavros
2007-01-01
The prospect for improving the success of ab initio zeolite structure investigations with electron diffraction data is evaluated. First of all, the quality of intensities obtained by precession electron diffraction at small hollow cone illumination angles is evaluated for seven representative materials: ITQ-1, ITQ-7, ITQ-29, ZSM-5, ZSM-10, mordenite, and MCM-68. It is clear that, for most examples, an appreciable fraction of a secondary scattering perturbation is removed by precession at small angles. In one case, ZSM-10, it can also be argued that precession diffraction produces a dramatically improved 'kinematical' data set. There seems to no real support for application of a Lorentz correction to these data and there is no reason to expect for any of these samples that a two-beam dynamical scattering relationship between structure factor amplitude and observed intensity should be valid. Removal of secondary scattering by the precession mode appears to facilitate ab initio structure analysis. Most zeolite structures investigated could be solved by maximum entropy and likelihood phasing via error-correcting codes when precession data were used. Examples include the projected structure of mordenite that could not be determined from selected area data alone. One anomaly is the case of ZSM-5, where the best structure determination in projection is made from selected area diffraction data. In a control study, the zonal structure of SSZ-48 could be determined from selected area diffraction data by either maximum entropy and likelihood or traditional direct methods. While the maximum entropy and likelihood approach enjoys some advantages over traditional direct methods (non-dependence on predicted phase invariant sums), some effort must be made to improve the figures of merit used to identify potential structure solutions
Electronic structure of silicon superlattices
International Nuclear Information System (INIS)
Krishnamurthy, S.; Moriarty, J.A.
1984-01-01
Utilizing a new complex-band-structure technique, the electronic structure of model Si-Si/sub 1-x/Ge/sub x/ and MOS superlattices has been obtained over a wide range of layer thickness d (11 less than or equal to d less than or equal to 110 A). For d greater than or equal to 44 A, it is found that these systems exhibit a direct fundamental band gap. Further calculations of band-edge effective masses and impurity scattering rates suggest the possibility of a band-structure-driven enhancement in electron mobility over bulk silicon
Ab initio study of isomerism of Li2AB2 molecules and Li2AB2+ ions with 16 valent electrons
International Nuclear Information System (INIS)
Charkin, O.P.; Klimenko, N.M.; MakKi, M.L.
2000-01-01
In the framework of MP2(6-31*//HF/6-31G + ZPE(HF/6-31G*) and MP4SDTQ/6-31G*//MP2/6-31G* + ZPE(MP2/6-31G*) approximations ab initio calculations of surfaces of potential energy of molecules of lithium salts of Li 2 AB 2 (Li 2 BeO 2 , L 2 MgO 2 , Li 2 BeS 2 , Li 2 MgS 2 , Li 2 CN 2 , Li 2 SiN 2 , Li 2 CP 2 ) type and ions of Li 2 AB 2 + (Li 2 BO 2 + , Li 2 AlO 2 + , Li 2 BS 2 + , Li 2 AlS 2 + , Li 2 N 3 + , Li 2 PN 2 + , Li 2 P 3 + ) type with 16 valent electrons are done. For oxide and nitride systems global minimum corresponds to symmetric linear structure D ∞h and for their sulfide and phosphorus analogues curved plane or unplane (C 2 ) structure with bond angle φ(LBA)=90-110 Deg are preferable. Equilibrium geometric parameters, relative energies and energies of isomer decomposition, frequencies and IR-intensities of normal vibrations are determined [ru
Ab initio study of dissociative attachment of low-energy electrons to F2
International Nuclear Information System (INIS)
Hazi, A.U.; Orel, A.E.; Rescigno, T.N.
1981-01-01
Adiabatic-nuclei resonance theory has been applied to the study of dissociative attachment of low-energy electrons to F 2 . Stieltjes moment theory was used to derive fixed-nuclei electronic resonance parameters from large scale configuration-interaction calculations on F 2 and F 2 - . Dissociative attachment cross sections are reported for the four lowest vibrational levels of F 2 and compared to available experimental data
Ab initio structures and stabilities of HeTM3+ (TM=Sc-Cu)
International Nuclear Information System (INIS)
Wilson, David J.D.; Marsden, Colin J.; Nagy-Felsobuki, Ellak I. von
2002-01-01
The electronic structure and molecular properties of triply charged transition metal helides, HeTM 3+ (where TM = Sc-Cu), have been investigated employing CCSD(T), MCSCF and MRCI methods. Dissociation energies and harmonic vibrational frequencies have also been determined. For all the triply charged helides, the ground state is dominated by the 3d n electronic configuration. In addition, states with configurations that have holes in the metal 3d σ orbital exhibit greater binding energies. The suitability of single-reference methods and diagnostics for this series has been investigated, with the MCSCF wave function being the most reliable diagnostic tool for the applicability of SCF methods
Ab initio transmission electron microscopy image simulations of coherent Ag-MgO interfaces
International Nuclear Information System (INIS)
Mogck, S.; Kooi, B.J.; Hosson, J.Th.M. de; Finnis, M.W.
2004-01-01
Density-functional theory calculations, within the plane-wave-ultrasoft pseudopotential framework, were performed in the projection for MgO and for the coherent (111) Ag-MgO polar interface. First-principles calculations were incorporated in high-resolution transmission electron microscopy (HRTEM) simulations by converting the charge density into electron scattering factors to examine the influence of charge transfer, charge redistribution at the interface, and ionicity on the dynamical electron scattering and on calculated HRTEM images. It is concluded that the ionicity of oxides and the charge redistribution at interfaces play a significant role in HRTEM image simulations. In particular, the calculations show that at oxygen-terminated (111) Ag-MgO interfaces the first oxygen layer at the interface is much brighter than that in calculations with neutral atoms, in agreement with experimental observations
Ab initio Calculations of Electronic Fingerprints of DNA bases on Graphene
Ahmed, Towfiq; Rehr, John J.; Kilina, Svetlana; Das, Tanmoy; Haraldsen, Jason T.; Balatsky, Alexander V.
2012-02-01
We have carried out first principles DFT calculations of the electronic local density of states (LDOS) of DNA nucleotide bases (A,C,G,T) adsorbed on graphene using LDA with ultra-soft pseudo-potentials. We have also calculated the longitudinal transmission currents T(E) through graphene nano-pores as an individual DNA base passes through it, using a non-equilibrium Green's function (NEGF) formalism. We observe several dominant base-dependent features in the LDOS and T(E) in an energy range within a few eV of the Fermi level. These features can serve as electronic fingerprints for the identification of individual bases from dI/dV measurements in scanning tunneling spectroscopy (STS) and nano-pore experiments. Thus these electronic signatures can provide an alternative approach to DNA sequencing.
Masrour, R.; Jabar, A.; Hlil, E. K.
2018-05-01
Self-consistent ab initio calculations, based on Density Functional Theory (DFT) approach and using Full potential Linear Augmented Plane Wave (FLAPW) method, are performed to investigate the electronic and magnetic properties of the Fe4N compound. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between Fe(I) and Fe(II) in Fe4N compound. We have used the obtained data from abinitio calculations as an input in Monte Carlo simulation to calculate the magnetic properties of this compounds such as the ground state phase diagrams, total and partial magnetization of Fe(I) and Fe(II) as well as the transition temperatures are computed. The variation of magnetization with the crystal field are also studied. The magnetic hysteresis cycle of the same Fe4N compound are determined for different values of temperatures and crystal field values. The two-step hysteresis loop are evidenced, which is typical for Fe4N structure. The ferromagnetic and superparamagnetic phase is observed as well.
Temperature dependence of the electronic structure of semiconductors and insulators
Energy Technology Data Exchange (ETDEWEB)
Poncé, S., E-mail: samuel.pon@gmail.com; Gillet, Y.; Laflamme Janssen, J.; Gonze, X. [European Theoretical Spectroscopy Facility and Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Chemin des étoiles 8, bte L07.03.01, B-1348 Louvain-la-neuve (Belgium); Marini, A. [Consiglio Nazionale delle Ricerche (CNR), Via Salaria Km 29.3, CP 10, 00016 Monterotondo Stazione (Italy); Verstraete, M. [European Theoretical Spectroscopy Facility and Physique des matériaux et nanostructures, Université de Liège, Allée du 6 Août 17, B-4000 Liège (Belgium)
2015-09-14
The renormalization of electronic eigenenergies due to electron-phonon coupling (temperature dependence and zero-point motion effect) is sizable in many materials with light atoms. This effect, often neglected in ab initio calculations, can be computed using the perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic harmonic approximation. After a short description of the recent progresses in this field and a brief overview of the theory, we focus on the issue of phonon wavevector sampling convergence, until now poorly understood. Indeed, the renormalization is obtained numerically through a slowly converging q-point integration. For non-zero Born effective charges, we show that a divergence appears in the electron-phonon matrix elements at q → Γ, leading to a divergence of the adiabatic renormalization at band extrema. This problem is exacerbated by the slow convergence of Born effective charges with electronic wavevector sampling, which leaves residual Born effective charges in ab initio calculations on materials that are physically devoid of such charges. Here, we propose a solution that improves this convergence. However, for materials where Born effective charges are physically non-zero, the divergence of the renormalization indicates a breakdown of the adiabatic harmonic approximation, which we assess here by switching to the non-adiabatic harmonic approximation. Also, we study the convergence behavior of the renormalization and develop reliable extrapolation schemes to obtain the converged results. Finally, the adiabatic and non-adiabatic theories, with corrections for the slow Born effective charge convergence problem (and the associated divergence) are applied to the study of five semiconductors and insulators: α-AlN, β-AlN, BN, diamond, and silicon. For these five materials, we present the zero-point renormalization, temperature dependence, phonon-induced lifetime broadening, and the renormalized electronic band structure.
Ab initio calculations on collisions of low energy electrons with polyatomic molecules
International Nuclear Information System (INIS)
Rescigno, T.N.
1991-01-01
The Kohn variational method is one of simplest, and oldest, techniques for performing scattering calculations. Nevertheless, a number of formal problems, as well as practical difficulties associated with the computation of certain required matrix elements, delayed its application to electron--molecule scattering problems for many years. This paper will describe the recent theoretical and computational developments that have made the ''complex'' Kohn variational method a practical tool for carrying out calculations of low energy electron--molecule scattering. Recent calculations on a number of target molecules will also be summarized. 41 refs., 7 figs
Odell, Anders; Delin, Anna; Johansson, Bö rje; Ulman, Kanchan; Narasimhan, Shobhana; Rungger, Ivan; Sanvito, Stefano
2011-01-01
The influence of the electrode's Fermi surface on the transport properties of a photoswitching molecule is investigated with state-of-the-art ab initio transport methods. We report results for the conducting properties of the two forms
Electronic structure and correlation effects in actinides
International Nuclear Information System (INIS)
Albers, R.C.
1998-01-01
This report consists of the vugraphs given at a conference on electronic structure. Topics discussed are electronic structure, f-bonding, crystal structure, and crystal structure stability of the actinides and how they are inter-related
Ballistic transport and electronic structure
Schep, Kees M.; Kelly, Paul J.; Bauer, Gerrit E.W.
1998-01-01
The role of the electronic structure in determining the transport properties of ballistic point contacts is studied. The conductance in the ballistic regime is related to simple geometrical projections of the Fermi surface. The essential physics is first clarified for simple models. For real
The Electronic Structure of Calcium
DEFF Research Database (Denmark)
Jan, J.-P.; Skriver, Hans Lomholt
1981-01-01
The electronic structure of calcium under pressure is re-examined by means of self-consistent energy band calculations based on the local density approximation and using the linear muffin-tin orbitals (LMTO) method with corrections to the atomic sphere approximation included. At zero pressure...
Electronic structure of metal clusters
International Nuclear Information System (INIS)
Wertheim, G.K.
1989-01-01
Photoemission spectra of valence electrons in metal clusters, together with threshold ionization potential measurements, provide a coherent picture of the development of the electronic structure from the isolated atom to the large metallic cluster. An insulator-metal transition occurs at an intermediate cluster size, which serves to define the boundary between small and large clusters. Although the outer electrons may be delocalized over the entire cluster, a small cluster remains insulating until the density of states near the Fermi level exceeds 1/kT. In large clusters, with increasing cluster size, the band structure approaches that of the bulk metal. However, the bands remain significantly narrowed even in a 1000-atom cluster, giving an indication of the importance of long-range order. The core-electron binding-energy shifts of supported metal clusters depend on changes in the band structure in the initial state, as well as on various final-state effects, including changes in core hole screening and the coulomb energy of the final-state charge. For cluster supported on amorphous carbon, this macroscopic coulomb shift is often dominant, as evidenced by the parallel shifts of the core-electron binding energy and the Fermi edge. Auger data confirm that final-state effects dominate in cluster of Sn and some other metals. Surface atom core-level shifts provide a valuable guide to the contributions of initial-state changes in band structure to cluster core-electron binding energy shifts, especially for Au and Pt. The available data indicate that the shift observed in supported, metallic clusters arise largely from the charge left on the cluster by photoemission. As the metal-insulator transition is approached from above, metallic screening is suppressed and the shift is determined by the local environment. (orig.)
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Hashemi, J.; Markussen, Troels
2009-01-01
Fullerene functionalized carbon nanotubes-NanoBuds-form a novel class of hybrid carbon materials, which possesses many advantageous properties as compared to the pristine components. Here, we report a theoretical study of the electronic transport properties of these compounds. We use both ab init...
Electronic and structural properties of B i2S e3:Cu
Sobczak, Kamil; Strak, Pawel; Kempisty, Pawel; Wolos, Agnieszka; Hruban, Andrzej; Materna, Andrzej; Borysiuk, Jolanta
2018-04-01
Electronic and structural properties of B i2S e3 and its extension to copper doped B i2S e3:Cu were studied using combined ab initio simulations and transmission electron microscopy based techniques, including electron energy loss spectroscopy, energy filtered transmission electron microscopy, and energy dispersive x-ray spectroscopy. The stability of the mixed phases was investigated for substitutional and intercalation changes of basic B i2S e3 structure. Four systems were compared: B i2S e3 , structures obtaining by Cu intercalation of the van der Waals gap, by substitution of Bi by Cu in quintuple layers, and C u2Se . The structures were identified and their electronic properties were obtained. Transmission electron microscopy measurements of B i2S e3 and the B i2S e3:Cu system identified the first structure as uniform and the second as composite, consisting of a nonuniform lower-Cu-content matrix and randomly distributed high-Cu-concentration precipitates. Critical comparison of the ab initio and experimental data identified the matrix as having a B i2S e3 dominant part with randomly distributed Cu-intercalated regions having 1Cu-B i2S e3 structure. The precipitates were determined to have 3Cu-B i2S e3 structure.
Orbital and magnetic structure of quasi-1D cobaltites: Ab initio calculations and experiment
International Nuclear Information System (INIS)
Pardo, V.; Baldomir, D.; Rivas, J.; Castro, J.; Arias, J.E.
2006-01-01
The magnetic properties of the orbitally degenerate quasi-one-dimensional cobaltites Sr x Ba 1-x CoO 3 are explained on the basis of a phase separation phenomenon. Noninteracting magnetic particles embedded in a nonferromagnetic matrix develop in the system. Details are given about the electronic and magnetic structure for x=0,0.2 and 0.5. At x=0.5, the geometry of the CoO 6 trigonally distorted octahedra changes by about 1-2%, but magnetic particles get 3 times bigger, compared to the parent compound, with the corresponding changes in the magnetic properties. The electronic structure of the Co 4+ ion, however, stays roughly unchanged
Electronic structure of Ag8GeS6
Directory of Open Access Journals (Sweden)
D.I. Bletskan
2017-04-01
Full Text Available For the first time, the energy band structure, total and partial densities of states of Ag8GeS6 crystal were calculated using the ab initio density functional method in LDA and LDA+U approximations. Argyrodite is direct-gap semiconductor with the calculated band gap width Egd = 1.46 eV in the LDA+U approximation. The valence band of argyrodite contains four energy separated groups of occupied subzones. The unique feature of electron-energy structure of Ag8GeS6 crystal is the energy overlapping between the occupied d-states of Ag atoms and the delocalized valence p-states of S atoms in relatively close proximity to the valence band top.
Structural, electronic and elastic properties of heavy fermion YbRh2 Laves phase compound
Pawar, Harsha; Shugani, Mani; Aynyas, Mahendra; Sanyal, Sankar P.
2018-05-01
The structural, electronic and elastic properties of YbRh2 Laves phase intermetallic compound which crystallize in cubic (MgCu2-type) structure have been investigated using ab-initio full potential linearized augmented plane wave (FP- LAPW) method with LDA and LDA+U approximation. The calculated ground state properties such as lattice parameter (a0), bulk modulus (B) and its pressure derivative (B') are in good agreement with available experimental and theoretical data. The electronic properties are analyzed from band structures and density of states. Elastic constants are predicted first time for this compound which obeys the stability criteria for cubic system.
Electronic structure and elasticity of Z-phases in the Cr–Nb–V–N system
Czech Academy of Sciences Publication Activity Database
Legut, D.; Pavlů, Jana
2012-01-01
Roč. 24, č. 19 (2012), s. 195502-195509 ISSN 0953-8984 R&D Projects: GA ČR(CZ) GAP108/10/1908; GA MŠk(CZ) ED1.1.00/02.0068 Institutional research plan: CEZ:AV0Z20410507 Keywords : ab initio calculations * Z-phase * Cr-Nb-V-N * electronic structure * elasticity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.355, year: 2012
An ab initio study of the structure and dynamics of bulk liquid Cd and its liquid-vapor interface
International Nuclear Information System (INIS)
Calderín, L; González, L E; González, D J
2013-01-01
Several static and dynamic properties of bulk liquid Cd at a thermodynamic state near its triple point have been calculated by means of ab initio molecular dynamics simulations. The calculated static structure shows a very good agreement with the available experimental data. The dynamical structure reveals collective density excitations with an associated dispersion relation which points to a small positive dispersion. Results are also reported for several transport coefficients. Additional simulations have also been performed at a slightly higher temperature in order to study the structure of the free liquid surface. The ionic density profile shows an oscillatory behavior with two different wavelengths, as the spacing between the outer and first inner layer is different from that between the other inner layers. The calculated reflectivity shows a marked maximum whose origin is related to the surface layering, along with a shoulder located at a much smaller wavevector transfer.
International Nuclear Information System (INIS)
Hofer, Thomas S.; Rode, Bernd M.; Randolf, Bernhard R.
2005-01-01
Structural properties of the hydrated Ba(II) ion have been investigated by ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations at double zeta HF quantum mechanical level. The first shell coordination number was found to be 9.3, and several other structural parameters such as angular distribution functions, radial distribution functions and tilt- and θ-angle distributions allowed the full characterization of the hydration structure of the Ba(II) ion in dilute aqueous solution. Velocity autocorrelation functions were used to calculate librational and vibrational motions, ion-ligand motions as well as reorientation times. Different dynamical parameters such as water reorientation, mean ligand residence time, the number of ligand exchange processes and rate constants were also analyzed and the ligand exchange rate constant for the first shell was determined as k = 5.3 x 10 10 s -1
International Nuclear Information System (INIS)
Anees, P; Valsakumar, M C; Chandra, Sharat; Panigrahi, B K
2014-01-01
Ab initio simulations have been performed to study the structure, energetics and stability of several plausible stacking sequences in graphite. These calculations suggest that in addition to the standard structures, graphite can also exist in AA-simple hexagonal, AB-orthorhombic and ABC-hexagonal type stacking. The free energy difference between these structures is very small (∼1 meV/atom), and hence all the structures can coexist from purely energetic considerations. Calculated x-ray diffraction patterns are similar to those of the standard structures for 2θ ⩽ 70°. Shear elastic constant C 44 is negative in AA-simple hexagonal, AB-orthorhombic and ABC-hexagonal structures, suggesting that these structures are mechanically unstable. Phonon dispersions show that the frequencies of some modes along the Γ–A direction in the Brillouin zone are imaginary in all of the new structures, implying that these structures are dynamically unstable. Incorporation of zero point vibrational energy via the quasi-harmonic approximation does not result in the restoration of dynamical stability. Potential energy surfaces for the unstable normal modes are seen to have the topography of a potential hill for all the new structures, confirming that all of the new structures are inherently unstable. The fact that the potential energy surface is not in the form of a double well implies that the structures are linearly as well as globally unstable. (paper)
DEFF Research Database (Denmark)
Palmer, Michael H.; Hoffmann, Søren Vrønning; Jones, Nykola C.
2011-01-01
The Rydberg states in the vacuum ultraviolet photoabsorption spectrum of 1,2,3-triazole have been measured and analyzed with the aid of comparison to the UV valence photoelectron ionizations and the results of ab initio configuration interaction (CI) calculations. Calculated electronic ionization...... and excitation energies for singlet, triplet valence, and Rydberg states were obtained using multireference multiroot CI procedures with an aug-cc-pVTZ [5s3p3d1f] basis set and a set of Rydberg [4s3p3d3f] functions. Adiabatic excitation energies obtained for several electronic states using coupled...... are the excitations consistent with an f-series....
Energy Technology Data Exchange (ETDEWEB)
Ismayilova, N. A., E-mail: ismayilova-narmin-84@mail.ru; Orudjev, H. S.; Jabarov, S. H. [Azerbaijan National Academy of Sciences, Institute of Physics (Azerbaijan)
2017-04-15
The results of ab initio calculations of the electron spectrum of TlFeS{sub 2} and TlFeSe{sub 2} crystals in the antiferromagnetic phase are reported. Calculations are carried out in the context of the density functional theory. The origin of the bands of s, p, and d electron states of Tl, Fe, S, and Se atoms is studied. It is established that, in the antiferromagnetic phase, the crystals possess semiconductor properties. The band gaps are found to be 0.05 and 0.34 eV for TlFeS{sub 2} and TlFeSe{sub 2} crystals, respectively.
Ab initio study on the electronic transport properties of carbon nanotube intramolecular junctions
Energy Technology Data Exchange (ETDEWEB)
Wang, R.N. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Graduate School of the Chinese Academy of Sciences, 19A Yu Quan Rd, Beijing 100049 (China); Zheng, X.H.; Zeng, Z. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Song, L.L. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Graduate School of the Chinese Academy of Sciences, 19A Yu Quan Rd, Beijing 100049 (China); School of Electronic Science and Applied Physics, Hefei University of Technology, Hefei 230009 (China)
2011-12-15
The effects of electron doping and molecule adsorption on the electronic transport properties of carbon nanotube (CNT) junctions CNT(3,3)/n-CNT(6,0)/CNT(3,3) (n = 1-5) are simulated by first-principles calculations combined with a non-equilibrium Green's function technique. The doping effects are investigated by N substitution for the carbon atom while the molecule adsorption effects are studied by adsorbing a H{sub 2}O molecule or an OH group on the top of one carbon atom, respectively. The transmission function around the Fermi level is highly dependent on the doping or adsorption site. The effects are negligible when the site is at the interface, while it always forms a scattering barrier which causes a valley of the transmission spectra around the Fermi level when the doping/adsorption site is inside the sandwiched CNT(6,0). The conductance of CNT intramolecular junctions is very sensitive to the environment, which may provide potential of application in future nanoelectronic devices and gas sensors. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Ren, Dahua; Xiang, Baoyan; Hu, Cheng; Qian, Kai; Cheng, Xinlu
2018-04-01
Hydrogen can be trapped in the bulk materials in four forms: interstitial molecular H2, interstitial atom H, O‑H+(2Si=O–H)+, Si‑H‑( {{4O}}\\bar \\equiv {{Si&x2212H}})‑ to affect the electronic and optical properties of amorphous silica. Therefore, the electronic and optical properties of defect-free and hydrogen defects in amorphous silica were performed within the scheme of density functional theory. Initially, the negative charged states hydrogen defects introduced new defect level between the valence band top and conduction band bottom. However, the neutral and positive charged state hydrogen defects made both the valence band and conduction band transfer to the lower energy. Subsequently, the optical properties such as absorption spectra, conductivity and loss functions were analyzed. It is indicated that the negative hydrogen defects caused the absorption peak ranging from 0 to 2.0 eV while the positive states produced absorption peaks at lower energy and two strong absorption peaks arose at 6.9 and 9.0 eV. However, the neutral hydrogen defects just improved the intensity of absorption spectrum. This may give insights into understanding the mechanism of laser-induced damage for optical materials. Project supported by the Science and Technology of Hubei Provincial Department of Education (No. B2017098).
Ab-initio study of structural, vibrational and optical properties of solid oxidizers
Energy Technology Data Exchange (ETDEWEB)
Yedukondalu, N.; Vaitheeswaran, G., E-mail: gvsp@uohyd.ernet.in
2016-09-15
We report the structural, elastic and vibrational properties of five ionic-molecular solid oxidizers MNO{sub 3} (M = Li, Na, K) and MClO{sub 3} (M = Na, K). By treating long range electron-correlation effects, dispersion corrected method leads to more accurate predictions of structural properties and phase stability of KNO{sub 3} polymorphs. The obtained elastic moduli show soft nature of these materials and are consistent with Ultrasonic Pulse Echo measurements. We made a complete assignment of vibrational modes which are in good accord with available experimental results. From calculated IR and Raman spectra, it is found that the vibrational frequencies show a red-shift from Li → Na → K (Na → K) and N → Cl for nitrates (chlorates) due to increase in mass of metal and non-metal atoms, respectively. The calculated electronic structure using recently developed Tran-Blaha modified Becke-Johnson potential show that the materials are wide band gap insulators with predominant ionic bonding between M{sup +} (metal) and NO{sub 3}{sup −}/ClO{sub 3}{sup −} ions and covalent bonding (N−O and Cl−O) within nitrate and chlorate anionic group. From the calculated optical spectra, we observe that electric-dipole transitions are due to nitrate/chlorate group below 20 eV and cationic transitions occur above 20 eV. The calculated reflectivity spectra are consistent with the available experimental measurements. - Highlights: • Ground state properties with inclusion of dispersion correction method. • Elastic constants and mechanical properties. • Vibrational spectra and their complete assignment. • Raman and IR spectra. • Electronic structure and optical properties using TB-mBJ potential.
Pietrucci, Fabio; Andreoni, Wanda
2011-08-01
Social permutation invariant coordinates are introduced describing the bond network around a given atom. They originate from the largest eigenvalue and the corresponding eigenvector of the contact matrix, are invariant under permutation of identical atoms, and bear a clear signature of an order-disorder transition. Once combined with ab initio metadynamics, these coordinates are shown to be a powerful tool for the discovery of low-energy isomers of molecules and nanoclusters as well as for a blind exploration of isomerization, association, and dissociation reactions.
Energy Technology Data Exchange (ETDEWEB)
Yaghlane, Saida Ben [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications – LSAMA, Université de Tunis, Tunis (Tunisia); Cotton, C. Eric; Francisco, Joseph S., E-mail: francisc@purdue.edu, E-mail: hochlaf@univ-mlv.fr [Department of Chemistry and Department of Earth and Atmospheric Science, Purdue University, West Lafayette, Indiana 49707 (United States); Linguerri, Roberto; Hochlaf, Majdi, E-mail: francisc@purdue.edu, E-mail: hochlaf@univ-mlv.fr [Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, Université Paris-Est, 5 bd Descartes, 77454 Marne-la-Vallée (France)
2013-11-07
Accurate ab initio computations of structural and spectroscopic parameters for the HPS/HSP molecules and corresponding cations and anions have been performed. For the electronic structure computations, standard and explicitly correlated coupled cluster techniques in conjunction with large basis sets have been adopted. In particular, we present equilibrium geometries, rotational constants, harmonic vibrational frequencies, adiabatic ionization energies, electron affinities, and, for the neutral species, singlet-triplet relative energies. Besides, the full-dimensional potential energy surfaces (PESs) for HPS{sup x} and HSP{sup x} (x = −1,0,1) systems have been generated at the standard coupled cluster level with a basis set of augmented quintuple-zeta quality. By applying perturbation theory to the calculated PESs, an extended set of spectroscopic constants, including τ, first-order centrifugal distortion and anharmonic vibrational constants has been obtained. In addition, the potentials have been used in a variational approach to deduce the whole pattern of vibrational levels up to 4000 cm{sup −1} above the minima of the corresponding PESs.
Ab initio study of low-energy electrons interacting with HCN molecules
International Nuclear Information System (INIS)
Jain, A.; Norcross, D.W.
1984-01-01
Our earlier study of low-energy electron scattering with HCN molecules is further improved by treating exchange exactly (in a separable exchange approximation 2 ) in Σ, π and Δ symmetries: the 3.8 eV π resonance is shifted towards lower energy (2.56 eV, the experimental position is around 2.26 eV 3 ), while in Σ and the Δ symmetries the difference is within 15%. We also study possible negative ion states of HCN by calculating potential energy curves with respect to C-H and C-N stretches. For example, there is evidence of an avoiding crossing between a 1Σ + and a 2Σ + state (C-H stretch) of HCN -
AB INITIO calculations of magneto-optical effects
Czech Academy of Sciences Publication Activity Database
Kuneš, Jan; Oppeneer, P. M.
2002-01-01
Roč. 2, - (2002), s. 141-146 ISSN 1346-7948 R&D Projects: GA AV ČR IAA1010214 Institutional research plan: CEZ:AV0Z1010914 Keywords : electronic structure * ab initio calculation * polar magneto-optical Kerr effect * transitiom metal * uranium intermetallics * CrO 2 Subject RIV: BM - Solid Matter Physics ; Magnetism
The Properties of Some Simple Covalent Hydrides: An Ab Initio ...
African Journals Online (AJOL)
Some properties of the monomeric binary hydrides of the elements of the first two rows of the periodic table have been determined using ab initio molecular orbital theory. The properties in question are the energetic, structural, electronic, topological and vibrational characteristics. In general, a gradual convergence towards ...
Georgieva, Miglena K.
2004-03-01
The structure of diazonium dicyanomethylide (diazodicyanomethane) +N 2-C(CN) 2-↔N 2C(CN) 2 has been studied on the basis of ab initio HF, MP2 and DFT BLYP force field calculations, as well as of literature IR spectra and X-ray diffraction structural data. The results have been compared with those obtained for a series of chemical relatives of the title compound, i.e. molecules, push-pull molecules, anions and zwitterions, containing α-dicyano or diazo fragments, and especially substituted ammonium dicyanomethylides and diazomethane +N 2-CH 2-↔N 2CH 2. It has been found on the basis of spectral, bond length, bond order and electric charge analyses that the diazonium (or carbanionic, left) canonical form is much more important for the title zwitterion, than the corresponding one for diazomethane. So, the title compound can be named (and considered as) both diazonium dicyanomethylide and dicyanodiazomethane.
FANG, CM; ETTEMA, ARHF; HAAS, C; WIEGERS, GA; VANLEUKEN, H; DEGROOT, RA
1995-01-01
In order to understand the electronic structure of the misfit-layer compound (SnS)(1.17)NbS2 we carried out an ab initio band-structure calculation of the closely related commensurate compound (SnS)(1.20)NbS2. The band structure is compared with calculations for NbS2 and for hypothetical SnS with
Fang, C.M.; Ettema, A.R.H.F.; Haas, C.; Wiegers, G.A.; Leuken, H. van; Groot, R.A. de
1995-01-01
In order to understand the electronic structure of the misfit-layer compound (SnS)1.17NbS2 we carried out an ab initio band-structure calculation of the closely related commensurate compound (SnS)1.20NbS2. The band structure is compared with calculations for NbS2 and for hypothetical SnS with
The atomic and electronic structure of amorphous silicon nitride
International Nuclear Information System (INIS)
Alvarez, F.; Valladares, A.A.
2002-01-01
Using a novel approach to the ab initio generation of random networks we constructed two nearly stoichiometric samples of amorphous silicon nitride with the same content x= 1.29. The two 64-atom periodically-continued cubic diamond-like cells contain 28 silicons and 36 nitrogens randomly substituted, and were amorphized with a 6 f s time step by heating them to just below their melting temperature with a Harris-functional based, molecular dynamics code in the LDA approximation. The averaged total radial distribution function (RDF) obtained is compared with some existing Tersoff-like potential simulations and with experiment; ours agree with experiment. All the partial radial features are calculated and the composition of the second peak also agrees with experiment. The electronic structure is calculated and the optical gaps obtained using both a HOMO-LUMO approach and the Tauc-like procedure developed recently that gives reasonable gaps. (Author)
International Nuclear Information System (INIS)
Verite, G.
2007-09-01
This research aims at determining, by means of DFT (density functional theory) electronic structure computations, the structure, the stability, and the mobility of isolated point defects, lack defects, auto-interstitial defects, or small aggregate defects in the compact hexagonal zirconium (hc Zr). After a literature survey on the studied materials and a review of computer simulation methods in material science, the author presents and comments the available results from experiments or simulations on point defects in hc Zr. He presents the growth phenomenon under radiation. Then, he briefly described the computing techniques used in this study, reports the determination of the network parameters and elastic constants of each material. He reports and comments the results obtained with the SIESTA code and with a Monte Carlo kinetic simulation. The different types of defects are investigated
Evolution of the electronic and ionic structure of Mg clusters with increase in cluster size
DEFF Research Database (Denmark)
Lyalin, Andrey G.; Solov'yov, Ilia; Solov'yov, Andrey V.
2003-01-01
The optimized structure and electronic properties of neutral and singly charged magnesium clusters have been investigated using ab initio theoretical methods based on density-functional theory and systematic post–Hartree-Fock many-body perturbation theory accounting for all electrons in the system....... We have investigated the appearance of the elements of the hcp structure and metallic evolution of the magnesium clusters, as well as the stability of linear chains and rings of magnesium atoms. The results obtained are compared with the available experimental data and the results of other...
Electronic structure of fractionally nuclear charged atoms
International Nuclear Information System (INIS)
Pavao, Antonio C.; Bastos, Cristiano C.; Ferreira, Joacy V.
2008-01-01
Different properties of quark chemistry are studied by performing accurate ab initio Hartree- Fock calculations on fractionally nuclear charged atoms. Ground and first excited states of sodium atoms with quarks attached to the nucleus are obtained using CI calculations. It is suggested that the sodium 2 P -> 2 S electronic transition can be used as a guide in searching for unconfined quarks. Also, the variation of the binding electronic energy with nuclear charge in the isoelectronic series of fractionally nuclear charged atoms A ±2/3 and A ±1/3 (A = H, Li, Na, P and Ca) is analyzed. The present calculations suggest that unconfined colored particles have large appetite for heavy nuclei and that quark-antiquark pairs could be stabilized in presence of the atomic matter. (author)
Electronic structure of lanthanide scandates
Mizzi, Christopher A.; Koirala, Pratik; Marks, Laurence D.
2018-02-01
X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and density functional theory calculations were used to study the electronic structure of three lanthanide scandates: GdSc O3,TbSc O3 , and DySc O3 . X-ray photoelectron spectra simulated from first-principles calculations using a combination of on-site hybrid and GGA +U methods were found to be in good agreement with experimental x-ray photoelectron spectra. The hybrid method was used to model the ground state electronic structure and the GGA +U method accounted for the shift of valence state energies due to photoelectron emission via a Slater-Janak transition state approach. From these results, the lanthanide scandate valence bands were determined to be composed of Ln 4 f ,O 2 p , and Sc 3 d states, in agreement with previous work. However, contrary to previous work the minority Ln 4 f states were found to be located closer to, and in some cases at, the valence band maximum. This suggests that minority Ln 4 f electrons may play a larger role in lanthanide scandate properties than previously thought.
Electronic structure of PPP@ZnO from all-electron quasiarticle calculations
Höffling, Benjamin; Nabok, Dimitri; Draxl, Claudia; Condensed Matter Theory Group, Humboldt University Berlin Team
We investigate the electronic properties of poly(para-phenylene) (PPP) adsorbed on the non-polar (001) surface of rocksalt (rs) ZnO using all-electron density functional theory (DFT) as well as quasiparticle (QP) calculations within the GW approach. A particular focus is put on the electronic band discontinuities at the interface, where we investigate the impact of quantum confinement, molecular polarization, and charge rearrangement. For our prototypical system, PPP@ZnO, we find a type-I heterostructure. Comparison of the band offsets derived from a QP-treatment of the hybrid system with predictions based on mesoscopic methods, like the Shockley-Anderson model or alignment via the electrostatic potential, reveals the inadequacy of these simple approaches for the prediction of the electronic structure of such inorganic/organic heterosystems. Finally, we explore the optical excitations of the interface compared to the features of the pristine components and discuss the methodological implications for the ab-initio treatment of interface electronics.
DEFF Research Database (Denmark)
Møgelhøj, Andreas; Kelkkanen, Kari André; Wikfeldt, K Thor
2011-01-01
The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations in the NVE ensemble using van der Waals (vdW) density-functional theory, i.e., using the new exchange-correlation functionals optPBE-vdW and vdW-DF2, where the latter has softer nonlocal...... protocol could cause the deviation. An O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from low-density liquid water, as extrapolated from experiments, reproduces near-quantitatively the experimental O-O PCF for ambient water. This suggests the possibility that the new functionals...... shows some resemblance with experiment for high-density water ( Soper , A. K. and Ricci , M. A. Phys. Rev. Lett. 2000 , 84 , 2881 ), but not directly with experiment for ambient water. Considering the accuracy of the new functionals for interaction energies, we investigate whether the simulation...
Energy Technology Data Exchange (ETDEWEB)
Pigozzi, Giancarlo; Janczak-Rusch, Jolanta; Passerone, Daniele; Antonio Pignedoli, Carlo; Patscheider, Joerg; Jeurgens, Lars P. H. [Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, CH-8600 Duebendorf (Switzerland); Antusek, Andrej [Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, CH-8600 Duebendorf (Switzerland); Faculty of Materials Science and Technology, Slovak University of Technology in Bratislava, Paulinska 16, 917 24 Trnava (Slovakia); Parlinska-Wojtan, Magdalena [Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, CH-8600 Duebendorf (Switzerland); University of Rzeszow, Institute of Physics, ul. Rejtana 16a, 35-959 Rzeszow (Poland); Bissig, Vinzenz [Kirsten Soldering AG, Hinterbergstrasse 32, CH-6330 Cham (Switzerland)
2012-10-29
Nano-sized Ag-Cu{sub 8nm}/AlN{sub 10nm} multilayers were deposited by reactive DC sputtering on {alpha}-Al{sub 2}O{sub 3}(0001) substrates. Investigation of the phase constitution and interface structure of the multilayers evidences a phase separation of the alloy sublayers into nanosized grains of Ag and Cu. The interfaces between the Ag grains and the quasi-single-crystalline AlN sublayers are semi-coherent, whereas the corresponding Cu/AlN interfaces are incoherent. The orientation relationship between Ag and AlN is constant throughout the entire multilayer stack. These observations are consistent with atomistic models of the interfaces as obtained by ab initio calculations.
Electron scattering and nuclear structure
International Nuclear Information System (INIS)
Frois, B.
1987-01-01
The search for the appropriate degrees of freedom to describe nuclei is the central focus of nuclear physics today. Therefore the authors explore in this review their current understanding of nuclear structure as defined by electromagnetic data. The precision of the electromagnetic probe allows us to define accurately the limits of present theoretical descriptions. The authors review here a broad range of subjects that have been addressed by recent experiments, from the study of meson exchange currents and single-particle distributions to collective excitations in heavy nuclei. However, they do not discuss elastic magnetic scattering, inelastic excitation of discrete states, or single-nucleon knockout reactions since these reactions were recently reviewed. The principal aim of this review is to offer a fresh perspective on nuclear structure, based on the new generation of electron scattering data presented here and in the above-mentioned articles
Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine
Srivastava, Santosh K.; Singh, Vipin B.
2013-11-01
Vibrational spectra and molecular structure of anhydrous caffeine have been systematically investigated by second order Moller-Plesset (MP2) perturbation theory and density functional theory (DFT) calculations. Vibrational assignments have been made and many previous ambiguous assignments in IR and Raman spectra are amended. The calculated DFT frequencies and intensities at B3LYP/6-311++G(2d,2p) level, were found to be in better agreement with the experimental values. It was found that DFT with B3LYP functional predicts harmonic vibrational wave numbers more close to experimentally observed value when it was performed on MP2 optimized geometry rather than DFT geometry. The calculated TD-DFT vertical excitation electronic energies of the valence excited states of anhydrous caffeine are found to be in consonance to the experimental absorption peaks.
Electronic structure of spin systems
Energy Technology Data Exchange (ETDEWEB)
Saha-Dasgupta, Tanusri
2016-04-15
Highlights: • We review the theoretical modeling of quantum spin systems. • We apply the Nth order muffin-tin orbital electronic structure method. • The method shows the importance of chemistry in the modeling. • CuTe{sub 2}O{sub 5} showed a 2-dimensional coupled spin dimer behavior. • Ti substituted Zn{sub 2}VO(PO{sub 4}){sub 2} showed spin gap behavior. - Abstract: Low-dimensional quantum spin systems, characterized by their unconventional magnetic properties, have attracted much attention. Synthesis of materials appropriate to various classes within these systems has made this field very attractive and a site of many activities. The experimental results like susceptibility data are fitted with the theoretical model to derive the underlying spin Hamiltonian. However, often such a fitting procedure which requires correct guess of the assumed spin Hamiltonian leads to ambiguity in deciding the representative model. In this review article, we will describe how electronic structure calculation within the framework of Nth order muffin-tin orbital (NMTO) based Wannier function technique can be utilized to identify the underlying spin model for a large number of such compounds. We will show examples from compounds belonging to vanadates and cuprates.
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, PB 63 46000 Safi (Morocco); Jabar, A. [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, PB 63 46000 Safi (Morocco); Hlil, E.K. [Institut Néel, CNRS, Université Grenoble Alpes, BP 166, F-38042 Grenoble cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Hourmatallah, A. [Equipe de Physique du Solide, Laboratoire LIPI, Ecole Normale Supérieure, BP 5206, Bensouda, Fes (Morocco); Rezzouk, A.; Bouslykhane, K.; Benzakour, N. [Laboratoire de Physique du Solide, Université Sidi Mohammed Ben Abdellah, Faculté des sciences DharMahraz, BP 1796, Fes (Morocco)
2017-04-15
Self-consistent ab initio calculations, based on Density Functional Theory (DFT) approach and using Full potential Linear Augmented Plane Wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Mn{sub 2}NiAl. Magnetic moment considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for Monte Carlo simulations to compute other magnetic parameters. Also, the magnetic properties of Mn{sub 2}NiAl are studied using the Monte Carlo simulations. The variation of magnetization and magnetic susceptibility with the reduced temperature of Mn{sub 2}NiAl are investigated. The transition temperature of this system is deduced for different values exchange interaction and crystal field. The thermal total magnetization has been obtained, and the magnetic hysteresis cycle is established. The total magnetic moment is superior to those obtained by the other method and is mainly determined by the antiparallel aligned Mn{sub I}, Mn{sub II} and Ni spin moments. The superparamagnetic phase is found at the neighborhood of transition temperature. - Highlights: • Ab initio calculations are used to study magnetic and electronic properties of Mn{sub 2}NiX. • The transition temperature of Mn{sub 2}NiX is established. • The magnetic hysteresis cycle of M{sub n2}NiX (X = Al, Ga, In, Sn) is deduced. • The magnetic coercive field of Mn{sub 2}NiX (X = Al, Ga, In, Sn) is given.
Ab initio study on half-metallic, electronic and thermodynamic attributes of LaFeO3
Tariq, Saad; Saad, Saher; Jamil, M. Imran; Sohail Gilani, S. M.; Mahmood Ramay, Shahid; Mahmood, Asif
2018-03-01
By using the density functional theory (DFT) the systematic study of the structural, electronic and thermodynamic properties of lanthanum ferrite (LaFeO3) has been conducted. The elastic stability criterion and structural tolerance factor reveal that LaFeO3 exists in the cubic phase and is found to be stable under the ambient conditions. In electronic properties, the optical spectrum of the compound has been found to fall in the range of 488 to 688nm which has been calculated from the electronic band gap values by using the PBE-GGA and mBJ-GGA techniques. The light between 488 to 688nm would cause the valence electrons to jump in the conduction band showing the photoconductivity. The pronounced half-metallic character has been discussed by using the projected electronic density of states. The ferromagnetic response has been observed which may be attributed to the Fe-O bonding situation. The compound exhibits ductile, indirect band gap and half-metallic traits in the bulk phase. We expect the compound to be felicitous for the novel spintronic applications.
Electronic structure of trypsin inhibitor from squash seeds in aqueous solution
Zheng, Haoping
2000-10-01
The electronic structure of the trypsin inhibitor from seeds of the squash Cucurbita maxima (CMTI-I) in aqueous solution is obtained by ab initio, all-electron, full-potential calculations using the self-consistent cluster-embedding (SCCE) method. The reactive site of the inhibitor is explained theoretically, which is in agreement with the experimental results. It is shown that the coordinates of oxygen atoms in the inhibitor, determined by nuclear magnetic resonance and combination of distance geometry and dynamical simulated annealing, are systematically less accurate than that of other kinds of heavy atoms.
Ali, Saima; Rashid, Muhammad; Hassan, M.; Noor, N. A.; Mahmood, Q.; Laref, A.; Haq, Bakhtiar Ul
2018-05-01
Owing to the large energy storage capacity and higher working voltage, the spinel oxides LiV2O4 and LiCr2O4, have remained under intense research attention for utilization as electrode materials in lithium-ion batteries. In this study, we explore the half-metallic nature and thermoelectric response in both LiV2O4 and LiCr2O4 spinel oxides using ab-initio density functional theory (DFT) based computations. The ground-state energies of these compounds have been studied at the optimized structural parameters in the ferromagnetic phase. In order to obtain a correct picture of the electronic structure and magnetic properties, the modified Becke-Johnson (mBJ) potential is applied to compute the electronic structures. The half-metallic behavior is confirmed by the spin-polarized electronic band structures and density of state plots. The magnetic nature is elucidated by computing the John-Teller energy, direct and indirect exchange and crystal field splitting energies. Our computations indicate strong hybridization decreasing the V/Cr site magnetic moments and increasing magnetic momenta at the nonmagnetic atomic sites. We also present the computed parameters significant for expressing the thermoelectric response, which are electrical conductivity, thermal conductivity, See-beck coefficient and power factor. The computed properties are of immense interest owing to the potential spintronics and Li-ion battery applications of the studied spinel materials.
Atomic and electronic structure of the CdTe(111)B–(2√3 × 4) orthogonal surface
Energy Technology Data Exchange (ETDEWEB)
Bekenev, V. L., E-mail: bekenev@ipms.kiev.ua; Zubkova, S. M. [National Academy of Sciences of Ukraine, Frantsevych Institute for Problems of Materials Science (Ukraine)
2017-01-15
The atomic and electronic structure of four variants of Te-terminated CdTe(111)B–(2√3 × 4) orthogonal polar surface (ideal, relaxed, reconstructed, and reconstructed with subsequent relaxation) are calculated ab initio for the first time. The surface is modeled by a film composed of 12 atomic layers with a vacuum gap of ~16 Å in the layered superlattice approximation. To close Cd dangling bonds on the opposite side of the film, 24 fictitious hydrogen atoms with a charge of 1.5 electrons each are added. Ab initio calculations are performed using the Quantum Espresso program based on density functional theory. It is demonstrated that relaxation leads to splitting of the four upper layers. The band energy structures and total and layer-by-layer densities of electronic states for the four surface variants are calculated and analyzed.
Electronic structure of semiconductor interfaces
Energy Technology Data Exchange (ETDEWEB)
Herman, F
1983-02-01
The study of semiconductor interfaces is one of the most active and exciting areas of current semiconductor research. Because interfaces play a vital role in modern semiconductor technology (integrated circuits, heterojunction lasers, solar cells, infrared detectors, etc.), there is a strong incentive to understand interface properties at a fundamental level and advance existing technology thereby. At the same time, technological advances such as molecular beam epitaxy have paved the way for the fabrication of semiconductor heterojunctions and superlattices of novel design which exhibit unusual electronic, optical, and magnetic properties and offer unique opportunities for fundamental scientific research. A general perspective on this subject is offered treating such topics as the atomic and electronic structure of semiconductor surfaces and interfaces; oxidation and oxide layers; semiconductor heterojunctions and superlattices; rectifying metal-semiconductor contacts; and interface reactions. Recent progress is emphasized and some future directions are indicated. In addition, the role that large-scale scientific computation has played in furthering our theoretical understanding of semiconductor surfaces and interfaces is discussed. Finally, the nature of theoretical models, and the role they play in describing the physical world is considered.
Electronic structure of semiconductor interfaces
International Nuclear Information System (INIS)
Herman, F.
1983-01-01
The study of semiconductor interfaces is one of the most active and exciting areas of current semiconductor research. Because interfaces play a vital role in modern semiconductor technology (integrated circuits, heterojunction lasers, solar cells, infrared detectors, etc.), there is a strong incentive to understand interface properties at a fundamental level and advance existing technology thereby. At the same time, technological advances such as molecular beam epitaxy have paved the way for the fabrication of semiconductor heterojunctions and superlattices of novel design which exhibit unusual electronic, optical, and magnetic properties and offer unique opportunities for fundamental scientific research. A general perspective on this subject is offered treating such topics as the atomic and electronic structure of semiconductor surfaces and interfaces; oxidation and oxide layers; semiconductor heterojunctions and superlattices; rectifying metal-semiconductor contacts; and interface reactions. Recent progress is emphasized and some future directions are indicated. In addition, the role that large-scale scientific computation has played in furthering our theoretical understanding of semiconductor surfaces and interfaces is discussed. Finally, the nature of theoretical models, and the role they play in describing the physical world is considered. (Author) [pt
Analysis of the zirconia structure by 'ab initio' and Rietveld methods
International Nuclear Information System (INIS)
Bechepeche, A.P.; Nasar, R.S.; Longo, E.; Treu Junior, O.; Varela, J.A.
1995-01-01
The zirconia was doped with 0,113 mol of Mg O e 0,005 mol of Ti O 2 , and it was calcined in 1550 d eg C and it was analyzed by XRD. The results shows that pure zirconia contains 96,19% of monoclinic phase and 3,18% of cubic. However, the doping magnesia stabilizes the zirconia in 17,24 of monoclinic; 29,63 of tetragonal and 53,13% of cubic phase. The addition of titanium in zirconia gives 25,85% of tetragonal phase and 37,66% of cubic, and this shows the no stabilizing action of this transition metal. By the other side, the results with ab-initio calculating shows the same tendency resulting in the next values of total energy: pure zirconia - monoclinic -11.316,86ua; tetragonal -8742,09 ua and cubic -8742,80 ua and Zr O 2 Ti O 2 system - monoclinic -9463,02 ua, tetragonal -9459,39 ua and cubic -9459,97 ua (author)
Ab initio-based approach to structural change of compound semiconductor surfaces during MBE growth
Ito, Tomonori; Akiyama, Toru; Nakamura, Kohji
2009-01-01
Phase diagrams of GaAs and GaN surfaces are systematically investigated by using our ab initio-based approach in conjunction with molecular beam epitaxy (MBE). The phase diagrams are obtained as a function of growth parameters such as temperature and beam equivalent pressure (BEP). The versatility of our approach is exemplified by the phase diagram calculations for GaAs(0 0 1) surfaces, where the stable phases and those phase boundaries are successfully determined as functions of temperature and As 2 and As 4 BEPs. The initial growth processes are clarified by the phase diagram calculations for GaAs(1 1 1)B-(2×2). The calculated results demonstrate that the As-trimer desorption on the GaAs(1 1 1)B-(2×2) with Ga adatoms occurs beyond 500-700 K while the desorption without Ga adatoms does beyond 800-1000 K. This self-surfactant effect induced by Ga adsorption crucially affects the initial growth of GaAs on the GaAs(1 1 1)B-(2×2). Furthermore, the phase diagram calculations for GaN(0 0 0 1) suggests that Ga adsorption or desorption during GaN MBE growth can easily change the pseudo-(1×1) to the (2×2)-Ga via newly found (1×1) and vice versa. On the basis of this finding, the possibility of ghost island formation during MBE growth is discussed.
International Nuclear Information System (INIS)
Mo, Shang-Di; Ching, W. Y.
2001-01-01
Ab initio calculation of the XANSE/ELNES spectra for α quartz and stishovite were carried out using a large-supercell approach that includes the electron - core - hole interaction. Excellent agreements with experimental spectra were obtained for Si - K, Si - L 2,3 , and O - K edges. The usual interpretation using orbital-resolved local density of states in the conduction band is unsatisfactory. [copyright] 2001 American Institute of Physics
Czech Academy of Sciences Publication Activity Database
Čurík, Roman; Šulc, M.
2010-01-01
Roč. 43, č. 17 (2010), s. 175205 ISSN 0953-4075 R&D Projects: GA MŠk(CZ) OC10046; GA MŠk OC09079; GA AV ČR KJB400400803; GA ČR GA202/08/0631 Institutional research plan: CEZ:AV0Z40400503 Keywords : Ab initio calculations * Commonly used * DFT potential Subject RIV: CF - Physical ; The oretical Chemistry Impact factor: 1.902, year: 2010
Energy Technology Data Exchange (ETDEWEB)
Nascimento, Daniel R.; DePrince, A. Eugene, E-mail: deprince@chem.fsu.edu [Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390 (United States)
2015-12-07
We present a combined cavity quantum electrodynamics/ab initio electronic structure approach for simulating plasmon-molecule interactions in the time domain. The simple Jaynes-Cummings-type model Hamiltonian typically utilized in such simulations is replaced with one in which the molecular component of the coupled system is treated in a fully ab initio way, resulting in a computationally efficient description of general plasmon-molecule interactions. Mutual polarization effects are easily incorporated within a standard ground-state Hartree-Fock computation, and time-dependent simulations carry the same formal computational scaling as real-time time-dependent Hartree-Fock theory. As a proof of principle, we apply this generalized method to the emergence of a Fano-like resonance in coupled molecule-plasmon systems; this feature is quite sensitive to the nanoparticle-molecule separation and the orientation of the molecule relative to the polarization of the external electric field.
Energy Technology Data Exchange (ETDEWEB)
Liu, Ping; Zhao, Jing; Liu, Jinxiang; Zhang, Meng; Bu, Yuxiang, E-mail: byx@sdu.edu.cn [School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100 (China)
2014-01-28
In view of the important implications of excess electrons (EEs) interacting with CO{sub 2}–H{sub 2}O clusters in many fields, using ab initio molecular dynamics simulation technique, we reveal the structures and dynamics of an EE associated with its localization and subsequent time evolution in heterogeneous CO{sub 2}–H{sub 2}O mixed media. Our results indicate that although hydration can increase the electron-binding ability of a CO{sub 2} molecule, it only plays an assisting role. Instead, it is the bending vibrations that play the major role in localizing the EE. Due to enhanced attraction of CO{sub 2}, an EE can stably reside in the empty, low-lying π{sup *} orbital of a CO{sub 2} molecule via a localization process arising from its initial binding state. The localization is completed within a few tens of femtoseconds. After EE trapping, the ∠OCO angle of the core CO{sub 2}{sup −} oscillates in the range of 127°∼142°, with an oscillation period of about 48 fs. The corresponding vertical detachment energy of the EE is about 4.0 eV, which indicates extreme stability of such a CO{sub 2}-bound solvated EE in [CO{sub 2}(H{sub 2}O){sub n}]{sup −} systems. Interestingly, hydration occurs not only on the O atoms of the core CO{sub 2}{sup −} through formation of O⋯H–O H–bond(s), but also on the C atom, through formation of a C⋯H–O H–bond. In the latter binding mode, the EE cloud exhibits considerable penetration to the solvent water molecules, and its IR characteristic peak is relatively red-shifted compared with the former. Hydration on the C site can increase the EE distribution at the C atom and thus reduce the C⋯H distance in the C⋯H–O H–bonds, and vice versa. The number of water molecules associated with the CO{sub 2}{sup −} anion in the first hydration shell is about 4∼7. No dimer-core (C{sub 2}O{sub 4}{sup −}) and core-switching were observed in the double CO{sub 2} aqueous media. This work provides molecular dynamics
Liu, Ping; Zhao, Jing; Liu, Jinxiang; Zhang, Meng; Bu, Yuxiang
2014-01-28
In view of the important implications of excess electrons (EEs) interacting with CO2-H2O clusters in many fields, using ab initio molecular dynamics simulation technique, we reveal the structures and dynamics of an EE associated with its localization and subsequent time evolution in heterogeneous CO2-H2O mixed media. Our results indicate that although hydration can increase the electron-binding ability of a CO2 molecule, it only plays an assisting role. Instead, it is the bending vibrations that play the major role in localizing the EE. Due to enhanced attraction of CO2, an EE can stably reside in the empty, low-lying π(*) orbital of a CO2 molecule via a localization process arising from its initial binding state. The localization is completed within a few tens of femtoseconds. After EE trapping, the ∠OCO angle of the core CO2 (-) oscillates in the range of 127°∼142°, with an oscillation period of about 48 fs. The corresponding vertical detachment energy of the EE is about 4.0 eV, which indicates extreme stability of such a CO2-bound solvated EE in [CO2(H2O)n](-) systems. Interestingly, hydration occurs not only on the O atoms of the core CO2 (-) through formation of O⋯H-O H-bond(s), but also on the C atom, through formation of a C⋯H-O H-bond. In the latter binding mode, the EE cloud exhibits considerable penetration to the solvent water molecules, and its IR characteristic peak is relatively red-shifted compared with the former. Hydration on the C site can increase the EE distribution at the C atom and thus reduce the C⋯H distance in the C⋯H-O H-bonds, and vice versa. The number of water molecules associated with the CO2 (-) anion in the first hydration shell is about 4∼7. No dimer-core (C2O4 (-)) and core-switching were observed in the double CO2 aqueous media. This work provides molecular dynamics insights into the localization and time evolution dynamics of an EE in heterogeneous CO2-H2O media.
Hydration structures of U(III) and U(IV) ions from ab initio molecular dynamics simulations
International Nuclear Information System (INIS)
Leung, Kevin; Nenoff, Tina M.
2012-01-01
We apply DFT+U-based ab initio molecular dynamics simulations to study the hydration structures of U(III) and U(IV) ions, pertinent to redox reactions associated with uranium salts in aqueous media. U(III) is predicted to be coordinated to 8 water molecules, while U(IV) has a hydration number between 7 and 8. At least one of the innershell water molecules of the hydrated U(IV) complex becomes spontaneously deprotonated. As a result, the U(IV)–O pair correlation function exhibits a satellite peak at 2.15 Å associated with the shorter U(IV)–(OH − ) bond. This feature is not accounted for in analysis of extended x-ray absorption fine structure and x-ray adsorption near edge structure measurements, which yield higher estimates of U(IV) hydration numbers. This suggests that it may be useful to include the effect of possible hydrolysis in future interpretation of experiments, especially when the experimental pH is close to the reported hydrolysis equilibrium constant value.
Mohamed, Tarek A; Shaltout, I; Al Yahyaei, K M
2006-05-01
Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO2+5%Fe2O3+10%TMO], where transition metal oxides (TMO) are TiO2, V2O5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm(-1)) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO4(4-) triagonal bipyramid (C2v) and Te2O7(6-) bridged tetrahedra (Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO3+1 binds to TeO3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three).
Lanzillo, Nicholas A.; Restrepo, Oscar D.; Bhosale, Prasad S.; Cruz-Silva, Eduardo; Yang, Chih-Chao; Youp Kim, Byoung; Spooner, Terry; Standaert, Theodorus; Child, Craig; Bonilla, Griselda; Murali, Kota V. R. M.
2018-04-01
We present a combined theoretical and experimental study on the electron transport characteristics across several representative interface structures found in back-end-of-line interconnect stacks for advanced semiconductor manufacturing: Cu/Ta(N)/Co/Cu and Cu/Ta(N)/Ru/Cu. In particular, we evaluate the impact of replacing a thin TaN barrier with Ta while considering both Co and Ru as wetting layers. Both theory and experiment indicate a pronounced reduction in vertical resistance when replacing TaN with Ta, regardless of whether a Co or Ru wetting layer is used. This indicates that a significant portion of the total vertical resistance is determined by electron scattering at the Cu/Ta(N) interface. The electronic structure of these nano-sized interconnects is analyzed in terms of the atom-resolved projected density of states and k-resolved transmission spectra at the Fermi level. This work further develops a fundamental understanding of electron transport and material characteristics in nano-sized interconnects.
Ab-initio Study of the Electron Mobility in a Functionalized UiO-66 Metal Organic Framework
Musho, Terence D.; Yasin, Alhassan S.
2018-03-01
This study leverages density functional theory accompanied with Boltzmann transport equation approaches to investigate the electronic mobility as a function of inorganic substitution and functionalization in a thermally stable UiO-66 metal-organic framework (MOF). The MOFs investigated are based on Zr-UiO-66 MOF with three functionalization groups of benzene dicarboxylate (BDC), BDC functionalized with an amino group (BDC + NH_2 ) and a nitro group (BDC + NO_2 ). The design space of this study is bound by UiO-66(M)-R, [M=Zr , Ti, Hf; R=BDC , BDC+NO_2 , BDC+NH_2 ]. The elastic modulus was not found to vary significantly over the structural modification of the design space for either functionalization or inorganic substitution. However, the electron-phonon scattering potential was found to be controllable by up to 30% through controlled inorganic substitution in the metal clusters of the MOF structure. The highest electron mobility was predicted for a UiO-66(Hf_5Zr_1 ) achieving a value of approximately 1.4× 10^{-3} cm^2 /V s. It was determined that functionalization provides a controlled method of modulating the charge density, while inorganic substitution provides a controlled method of modulating the electronic mobility. Within the proposed design space the electrical conductivity was able to be increased by approximately three times the base conductivity through a combination of inorganic substitution and functionalization.
Energy Technology Data Exchange (ETDEWEB)
Fatima, Bushra, E-mail: bushrafatima25@gmail.com; Acharya, Nikita; Sanyal, Sankar P. [Department of Physics, Barkatullah University, Bhopal, 462026 (India)
2016-05-06
The structural stability, electronic structure, elastic and mechanical properties of TiZn and ZrZn intermetallics have been studied using ab-initio full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation for exchange and correlation potentials. The various structural parameters, such as lattice constant (a{sub 0}), bulk modulus (B), and its pressure derivative (B’) are analysed and compared. The investigation of elastic constants affirm that both TiZn and ZrZn are elastically stable in CsCl (B{sub 2} phase) structure. The electronic structures have been analysed quantitatively from the band structure which reveals the metallic nature of these compounds. To better illustrate the nature of bonding and charge transfer, we have also studied the Fermi surfaces. The three well known criterion of ductility namely Pugh’s rule, Cauchy’s pressure and Frantsevich rule elucidate the ductile nature of these compounds.
Makinistian, Leonardo; Albanesi, Eduardo A.
2013-06-01
We present ab initio calculations of magnetoelectronic and transport properties of the interface of hcp Cobalt (001) and the intrinsic narrow-gap semiconductor germanium selenide (GeSe). Using a norm-conserving pseudopotentials scheme within DFT, we first model the interface with a supercell approach and focus on the spin-resolved densities of states and the magnetic moment (spin and orbital components) at the different atomic layers that form the device. We also report a series of cuts (perpendicular to the plane of the heterojunction) of the electronic and spin densities showing a slight magnetization of the first layers of the semiconductor. Finally, we model the device with a different scheme: using semiinfinite electrodes connected to the heterojunction. These latter calculations are based upon a nonequilibrium Green's function approach that allows us to explore the spin-resolved electronic transport under a bias voltage (spin-resolved I-V curves), revealing features of potential applicability in spintronics.
Energy Technology Data Exchange (ETDEWEB)
Bechepeche, A.P.; Nasar, R.S.; Longo, E. [Sao Carlos Univ., SP (Brazil). Dept. de Quimica; Treu Junior, O.; Varela, J.A. [UNESP, Araraquara, SP (Brazil). Inst. de Quimica
1995-12-31
The zirconia was doped with 0,113 mol of Mg O e 0,005 mol of Ti O{sub 2}, and it was calcined in 1550{sup d}eg C and it was analyzed by XRD. The results shows that pure zirconia contains 96,19% of monoclinic phase and 3,18% of cubic. However, the doping magnesia stabilizes the zirconia in 17,24 of monoclinic; 29,63 of tetragonal and 53,13% of cubic phase. The addition of titanium in zirconia gives 25,85% of tetragonal phase and 37,66% of cubic, and this shows the no stabilizing action of this transition metal. By the other side, the results with ab-initio calculating shows the same tendency resulting in the next values of total energy: pure zirconia - monoclinic -11.316,86ua; tetragonal -8742,09 ua and cubic -8742,80 ua and Zr O{sub 2} Ti O{sub 2} system - monoclinic -9463,02 ua, tetragonal -9459,39 ua and cubic -9459,97 ua (author) 3 figs., 2 tabs.
Energy Technology Data Exchange (ETDEWEB)
Gendron, Frederic; Pritchard, Ben; Autschbach, Jochen [Department of Chemistry, University at Buffalo, State University of New York, Buffalo, NY (United States); Paez-Hernandez, Dayan; Bolvin, Helene [Laboratoire de Physique et de Chimie Quantiques, Universite Toulouse 3 (France); Notter, Francois-Paul [Laboratoire de Chimie Quantique, Universite de Strasbourg (France)
2014-06-23
The electronic structure and magnetic properties of neptunyl(VI), NpO{sub 2}{sup 2+}, and two neptunyl complexes, [NpO{sub 2}(NO{sub 3}){sub 3}]{sup -} and [NpO{sub 2}Cl{sub 4}]{sup 2-}, were studied with a combination of theoretical methods: ab initio relativistic wavefunction methods and density functional theory (DFT), as well as crystal-field (CF) models with parameters extracted from the ab initio calculations. Natural orbitals for electron density and spin magnetization from wavefunctions including spin-orbit coupling were employed to analyze the connection between the electronic structure and magnetic properties, and to link the results from CF models to the ab initio data. Free complex ions and systems embedded in a crystal environment were studied. Of prime interest were the electron paramagnetic resonance g-factors and their relation to the complex geometry, ligand coordination, and nature of the nonbonding 5f orbitals. The g-factors were calculated for the ground and excited states. For [NpO{sub 2}Cl{sub 4}]{sup 2-}, a strong influence of the environment of the complex on its magnetic behavior was demonstrated. Kohn-Sham DFT with standard functionals can produce reasonable g-factors as long as the calculation converges to a solution resembling the electronic state of interest. However, this is not always straightforward. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Konstantinou, Konstantinos; Sushko, Peter V; Duffy, Dorothy M
2016-09-21
The nature of chemical bonding of molybdenum in high level nuclear waste glasses has been elucidated by ab initio molecular dynamics simulations. Two compositions, (SiO 2 ) 57.5 -(B 2 O 3 ) 10 -(Na 2 O) 15 -(CaO) 15 -(MoO 3 ) 2.5 and (SiO 2 ) 57.3 -(B 2 O 3 ) 20 -(Na 2 O) 6.8 -(Li 2 O) 13.4 -(MoO 3 ) 2.5 , were considered in order to investigate the effect of ionic and covalent components on the glass structure and the formation of the crystallisation precursors (Na 2 MoO 4 and CaMoO 4 ). The coordination environments of Mo cations and the corresponding bond lengths calculated from our model are in excellent agreement with experimental observations. The analysis of the first coordination shell reveals two different types of molybdenum host matrix bonds in the lithium sodium borosilicate glass. Based on the structural data and the bond valence model, we demonstrate that the Mo cation can be found in a redox state and the molybdate tetrahedron can be connected with the borosilicate network in a way that inhibits the formation of crystalline molybdates. These results significantly extend our understanding of bonding in Mo-containing nuclear waste glasses and demonstrate that tailoring the glass composition to specific heavy metal constituents can facilitate incorporation of heavy metals at high concentrations.
Rangan, Sylvie; Bartynski, Robert A.; Narasimhan, Amrit; Brainard, Robert L.
2017-07-01
The electronic structure of extreme ultra violet resist materials and of their individual components, two polymers and two photoacid generators (PAGs), is studied using a combination of x-ray and UV photoemission spectroscopies, electron energy loss spectroscopy, and ab-initio techniques. It is shown that simple molecular models can be used to understand the electronic structure of each sample and describe the experimental data. Additionally, effects directly relevant to the photochemical processes are observed: low energy loss processes are observed for the phenolic polymer containing samples that should favor thermalization of electrons; PAG segregation is measured at the surface of the resist films that could lead to surface inhomogeneities; both PAGs are found to be stable upon irradiation in the absence of the polymer, contrasting with a high reactivity that can be followed upon x-ray irradiation of the full resist.
Energy Technology Data Exchange (ETDEWEB)
Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Shaw, D.A. [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Stener, M.; Decleva, P. [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unità di Trieste (Italy); CNR-IOM, Trieste (Italy); Coriani, S. [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unità di Trieste (Italy); Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C (Denmark)
2016-09-30
Highlights: • The valence shell photoabsorption spectrum of s-triazine has been measured. • Electronic structure calculated with TDDFT and coupled cluster approaches. • Assignments proposed for Rydberg and valence states. • Mixing between Rydberg and valence states important. - Abstract: The absolute photoabsorption cross section of s-triazine has been measured between 4 and 40 eV, and is dominated by bands associated with valence states. Structure due to Rydberg excitations is both weak and irregular. Jahn-Teller interactions affect the vibronic structure observed in the Rydberg absorption bands due to excitation from the 1e″ or 6e′ orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important.
Energetic, electronic and optical properties of lanthanide doped TiO2: An ab initio LDA+U study
CSIR Research Space (South Africa)
Mulwa, WM
2016-05-01
Full Text Available potential, J. Chem. Phys. 118 (2003) 8207. doi:10.1063/1.1564060. [23] X. Ren, Beyond LDA and GGA - Tackling exact exchange , hybrid functional , MP2 , and RPA with numeric atom-centered orbitals The Fritz-Haber-Institute ab initio molecular simulations.... Calzolari, A. Ruini, A. Catellani, Anchor Group versus Conjugation: Toward the Gap-State Engineering of Functionalized ZnO (101̅0) Surface for Optoelectronic Applications, J. Am. Chem. Soc. 133 (2011) 5893–5899. [36] R. Gillen, S.J. Clark, J. Robertson...
International Nuclear Information System (INIS)
Mahmood, Q; Alay-e-Abbas, S M; Mahmood, I; Noor, N A; Asif, Mahmood
2016-01-01
The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic (FM) Mg 0.75 TM 0.25 Te (TM = Fe, Co, Ni) in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local (spin) density approximation (mBJLDA) is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mg 0.75 TM 0.25 Te alloys in the FM phase are also presented. For electronic properties, the spin-polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the (110) plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites (Fe, Co, Ni), as well as at the non-magnetic sites (Mg, Te). It is found that the p–d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites. (paper)
Ab-initio study of electronic and magnetic properties of Co-doped Mo2C monolayer
Mehta, Veenu; Tankeshwar, K.; Saini, Hardev S.
2018-05-01
The spin polarized density functional theory (DFT) based calculations has been performed to investigate the electronic and magnetic properties of pristine and Co-doped Mo2C using VASP code. The calculated results show that the pristine Mo2C is found to be non-magnetic whereas the Co dopant at Mo-site in the Mo2C monolayer generates the ferromagnetism in the resultant compound. The total magnetic moment of the system has been found to be 1.2µB which increases to 2.03µB as the concentration of Co increase from 3% to 8%, respectively. The electronic structure calculations of the pristine and Co-doped Mo2C show its metallic behavior which may found its application in magnetic energy storage devices, magnetic tape etc.
Electronic structure and interatomic bonding in Al10V
International Nuclear Information System (INIS)
Jahnatek, M; Krajci, M; Hafner, J
2003-01-01
On the basis of ab initio calculations we analysed the electron density distribution in the elementary cell of the compound Al 10 V. We found covalent bonding between certain atoms. The Al-V bonds of enhanced covalency are linked into -Al-V-Al-V- chains that extend over the whole crystal. The chains intersect at each V site and together form a Kagome network of corner-sharing tetrahedra. The large voids of this network are filled by Z 16 Friauf polyhedra consisting of Al atoms only. The skeleton of the Friauf polyhedron has the form of a truncated tetrahedron and consists of 12 strongly bonded Al atoms. These Al-Al bonds also have covalent character. The bonding is dominated by sp 2 hybridization. The centre of the Friauf polyhedron may be empty or occupied by an Al atom. The thermodynamic stability of the phase is investigated. The Al 21 V 2 phase with occupied voids is at low temperatures less stable than Al 10 V. The Al 10 V structure can be considered as a special case of the Al 18 Cr 2 Mg 3 structural class. We have found the same picture of bonding as we report here for Al 10 V for several other aluminium-rich alloys belonging to the Al 18 Cr 2 Mg 3 structural class also
Homologous series of layered structures in binary and ternary Bi-Sb-Te-Se systems : Ab initio study
Govaerts, K.; Sluiter, M.H.F.; Partoens, B.; Lamoen, D.
2014-01-01
In order to account explicitly for the existence of long-periodic layered structures and the strong structural relaxations in the most common binary and ternary alloys of the Bi-Sb-Te-Se system, we have developed a one-dimensional cluster expansion (CE) based on first-principles electronic structure
Byrne, Aaron; English, Niall J.; Schwingenschlö gl, Udo; Coker, David F.
2015-01-01
Ab initio, density functional theory (DFT)-based molecular dynamics (MD) has been carried out to investigate the effect of explicit solvation on the dynamical and structural properties of a [bmim][NTf2] room-temperature ionic liquid (RTIL
Pawar, H.; Shugani, M.; Aynyas, M.; Sanyal, S. P.
2018-02-01
The structural, electronic and elastic properties of YbTM2 (TM = Ir and Pt) Laves phase intermetallic compounds which crystallize in cubic (MgCu2-type) structure, have been investigated using ab-initio full potential linearized augmented plane wave (FP-LAPW) method with LDA and LDA+U approximation. The calculated ground state properties such as lattice parameter (a0), bulk modulus (B) and its pressure derivative (B‧) are in good agreement with available experimental and theoretical data. The electronic properties are analyzed from band structures and density of states. Elastic constants are predicted first time for these compounds which obey the stability criteria for cubic system.
Bryce, Richard A.; Vincent, Mark A.; Malcolm, Nathaniel O. J.; Hillier, Ian H.; Burton, Neil A.
1998-08-01
A new hybrid quantum mechanical/molecular mechanical model of solvation is developed and used to describe the structure and dynamics of small fluoride/water clusters, using an ab initio wave function to model the ion and a fluctuating charge potential to model the waters. Appropriate parameters for the water-water and fluoride-water interactions are derived, with the fluoride anion being described by density functional theory and a large Gaussian basis. The role of solvent polarization in determining the structure and energetics of F(H2O)4- clusters is investigated, predicting a slightly greater stability of the interior compared to the surface structure, in agreement with ab initio studies. An extended Lagrangian treatment of the polarizable water, in which the water atomic charges fluctuate dynamically, is used to study the dynamics of F(H2O)4- cluster. A simulation using a fixed solvent charge distribution indicates principally interior, solvated states for the cluster. However, a preponderance of trisolvated configurations is observed using the polarizable model at 300 K, which involves only three direct fluoride-water hydrogen bonds. Ab initio calculations confirm this trisolvated species as a thermally accessible state at room temperature, in addition to the tetrasolvated interior and surface structures. Extension of this polarizable water model to fluoride clusters with five and six waters gave less satisfactory agreement with experimental energies and with ab initio geometries. However, our results do suggest that a quantitative model of solvent polarization is fundamental for an accurate understanding of the properties of anionic water clusters.
Energy Technology Data Exchange (ETDEWEB)
Wagner, Jan-Martin
2004-10-14
In this dissertation, ab-initio investigations of the strain influence on vibrational properties of GaN and AlN as well as of short-period GaN/AlN superlattices are presented. Based on densityfunctional theory and density-functional perturbation theory, for differently strained structures complete phonon spectra and related properties are calculated using the local-density approximation and norm-conserving pseudopotentials. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Bryant, Pamela L.; Harwell, Chris; Mrse, Anthony A.; Emery, Earl F.; Gan, Zhedong; Caldwell, Tod; Reyes, Arneil P.; Kuhns, Philip; Hoyt, David W.; Simeral, Larry S.; Hall, Randall W.; Butler, Leslie G.
2001-11-07
Aminato and propanolato aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three 27Al NMR techniques optimized for large 27Al Quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. The 27Al quadrupole coupling constants and asymmetry parameters of molecular species, both experimental and derived from ab initio molecular orbital calculations, are correlated with structure.
Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals
Directory of Open Access Journals (Sweden)
Noor A. Nama
2010-01-01
Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001-(1×1 surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.
Electronic structure and mechanical properties of Cr7C3
International Nuclear Information System (INIS)
Music, D.; Kreissig, U.; Mertens, R.; Schneider, J.M.
2004-01-01
We have studied the Cr 7 C 3 phase by means of ab initio calculations and found covalent-ionic Cr-C-Cr chains in a metallic matrix. Furthermore, the structure of thin films, synthesized by RF magnetron sputtering, is shown to be in good agreement with our theoretical prediction
Ab-initio calculations of superconducting properties of YBa2Cu3O7
International Nuclear Information System (INIS)
Zhao, G.L.; Bagayoko, D.
1999-01-01
The authors present ab-initio calculations for the electronic structure and superconducting properties of YBa 2 Cu 3 O 7 (YBCO). The electronic structure was calculated using a self-consistent ab-initio LCAO method. They solved the anisotropic Eliashberg gap equation numerically. The strong coupling of the high energy optical phonons around 60--73 meV, with the electrons at the Fermi surface, leads to a high Tc in YBCO. The calculated Tc is about 89 K for μ* = 0.1. The good agreement of the calculated results with experimental measurements and the ab-initio nature of the calculations support the scenario of an anisotropic s-wave superconductor for YBCO
Ab-initio studies of the electronic and optical properties of Al2O3:Ti3+ laser crystals
Brik, M. G.
2018-03-01
The structural and electronic properties of pure and Ti3+-doped α-Al2O3 were calculated in the present paper by using the first-principles methods. Special attention has been paid to the location of the Ti3+ states (3d1 electron configuration) in the band gap; the lowest 3d states are at about 4.78 eV above the top of the valence band. The crystal field strength 10Dq at the Ti3+ site was estimated from the density of states diagrams to be about 17,700 cm-1. The structural optimization of the unit cell was also performed at elevated hydrostatic pressure in the range from 0 to 25 GPa. By application of the Murnaghan equation to the obtained results, the bulk modulus of α-Al2O3 was estimated to be 225.69 GPa. In addition, from the analysis of the Ti3+3d density of states the distance dependence of the crystal field strength was found to be described by the following function: 10Dq=61.744/R4.671, where R is expressed in Å and 10Dq in eV.
Ab initio study of phase transition of boron nitride between zinc-blende and rhombohedral structures
Energy Technology Data Exchange (ETDEWEB)
Nishida, S.; Funashima, H.; Sato, K.; Katayama-Yoshida, H. [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
2013-12-04
Boron nitride has polymorphs such as zinc-blende (c-BN), wurtzite (w-BN), rhombohedral (r-BN), and graphite-like (h-BN) forms. We simulate the direct conversion of r-BN to c-BN through electronic excitation. In our calculation, the conversion is made possible by increasing the hole concentration to over 0.06/atom. This conversion should be experimentally possible by hole-doping via an electric double layer transistor (EDLT) or capacitor.
Electronic structure studies of fullerites and fullerides
International Nuclear Information System (INIS)
Merkel, M.; Sohmen, E.; Masaki, A.; Romberg, H.; Alexander, M.; Knupfer, M.; Golden, M.S.; Adelmann, P.; Renker, B.; Fink, J.
1993-01-01
The electronic structure of fullerites and fullerides has been investigated by high-resolution photoemission and by high-energy electron energy-loss spectroscopy in transmission. Information on the occupied Π and σ bands, on the unoccupied Π * and σ * bands, and on the joint density of states has been obtained. In particular, we report on the changes of the electronic structure of fullerides as a function of dopant concentration. (orig.)
The general atomic and molecular electronic structure system HONDO: Version 7.0
International Nuclear Information System (INIS)
Dupuis, M.; Watts, J.D.; Villar, H.O.; Hurst, G.J.B.
1989-01-01
We describe a computer program for ab initio quantum mechanical calculations of atomic and molecular wavefunctions and energies. Capabilities for the calculation of energy gradients and second derivatives with respect to nuclear coordinates are provided for several types of wavefunctions. Calculations of many molecular properties based on the electron density are possible. The program contains automated algorithms for the determination of equilibrium structures, saddle points, reaction pathways, vibrational spectra including infrared and Raman intensities. We illustrate the capabilities of the program by highlighting research problems recently investigated with the present program. (orig.)
On the Electronic Structure of [Cu(H2O)6]2+
DEFF Research Database (Denmark)
Tanaka, Kiyoshi; Johansen, Helge
1997-01-01
The electronic structure of the ground state and doublet excited states due to d-d transitions and charge transfer transitions from ligand to copper of [Cu(H2O)6]2+ are investigated by ab initio calculations. The excited states corresponding to the the d-d transitions are calculated to be 1.1 - 1...... on the description of these excited states. The chargetransfer excitations are predicted to start around 6.5 eV for [Cu(H2O)6]2+....
International Nuclear Information System (INIS)
Godunov, I.A.; Bataev, V.A.; Maslov, D.V.; Yakovlev, N.N.
2017-01-01
The structure of conformational non-rigid molecules in the excited electronic states are investigated by joint theoretical and experimental methods. The theoretical part of work consist of two stages. In first stage the ab initio quantum-chemical calculations are carried out using high level methods. In second stage the vibrational problems of the various dimensions are solved by variational method for vibrations of large amplitude. In experimental part of work the vibronic spectra are investigated: gas-phase absorption and also, fluorescence excitation spectra of jet-cooled molecules. Some examples are considered.
Energy Technology Data Exchange (ETDEWEB)
Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)
2014-04-24
A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.
Solvated electron structure in glassy matrices
International Nuclear Information System (INIS)
Kevan, L.
1981-01-01
Current knowledge of the detailed geometrical structure of solvated electrons in aqueous and organic media is summarized. The geometry of solvated electrons in glassy methanol, ethanol, and 2-methyltetrahydrofuran is discussed. Advanced electron magnetic resonance methods and development of new methods of analysis of electron spin echo modulation patterns, second moment line shapes, and forbidden photon spin-flip transitions for paramagnetic species in these disordered systems are discussed. 66 references are cited
Energy Technology Data Exchange (ETDEWEB)
Ventelon, L
2008-11-15
The various methods appropriate for the simulation of dislocations within first-principles calculations have been set up, improved and compared between them. They have been applied to study screw dislocations in body-centered cubic iron using the SIESTA code. A non-degenerate core structure is obtained; its detailed analysis reveals a dilatation effect. Taking it into account in an anisotropic elasticity model, allows explaining the cell-size dependence of the energetics, obtained within the dipole approach. The Peierls potential obtained in ab initio suggests that the metastable core configuration at halfway position in the Peierls barrier, predicted by empirical potential, does not exist. We show how to construct tri-periodic cells optimized to study kinked dislocations. Using empirical potential, we demonstrate the feasibility of ab initio calculations of Peierls stress and kink formation. (author)
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.
Tailoring atomic structure to control the electronic transport in zigzag graphene nanoribbon
International Nuclear Information System (INIS)
Zeng, Hui; Zhao, Jun; Wei, Jianwei; Zeng, Xianliang; Xu, Yang
2012-01-01
We have performed ab initio density functional theory calculation to study the electronic transport properties of the tailored zigzag-edged graphene nanoribbon (ZGNR) with particular electronic transport channels. Our results demonstrated that tailoring the atomic structure had significantly influenced the electronic transport of the defective nanostructures, and could lead to the metal-semiconducting transition when sufficient atoms are tailored. The asymmetric I–V characteristics as a result of symmetry breaking have been exhibited, which indicates the route to utilize GNR as a basic component for novel nanoelectronics. -- Highlights: ► M–S transition induced by tailoring nanostructure. ► Asymmetric I–V curve due to symmetry breaking. ► Controllable electron transport by designing nanofiguration.
Tailoring atomic structure to control the electronic transport in zigzag graphene nanoribbon
Energy Technology Data Exchange (ETDEWEB)
Zeng, Hui [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Zhao, Jun, E-mail: zhaojun@yangtzeu.edu.cn [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Wei, Jianwei [College of Optoelectronic Information, Chongqing University of Technology, Chongqing 400054 (China); Zeng, Xianliang [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Xu, Yang [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou, Zhejiang 310027 (China)
2012-10-01
We have performed ab initio density functional theory calculation to study the electronic transport properties of the tailored zigzag-edged graphene nanoribbon (ZGNR) with particular electronic transport channels. Our results demonstrated that tailoring the atomic structure had significantly influenced the electronic transport of the defective nanostructures, and could lead to the metal-semiconducting transition when sufficient atoms are tailored. The asymmetric I–V characteristics as a result of symmetry breaking have been exhibited, which indicates the route to utilize GNR as a basic component for novel nanoelectronics. -- Highlights: ► M–S transition induced by tailoring nanostructure. ► Asymmetric I–V curve due to symmetry breaking. ► Controllable electron transport by designing nanofiguration.
Electron scattering and nuclear structure
International Nuclear Information System (INIS)
Wolynec, E.
1985-01-01
A review of the historical development and the theory necessary to the interpretation of the experimental results is made. Some measurement techniques, experimental results and the technique of analysis of these data are presented. Future perspectives, due to the appearence of continous electron current accelerators, in this field of study are discussed. (L.C.) [pt
Electron gun controlled smart structure
Martin, Jeffrey W.; Main, John Alan; Redmond, James M.; Henson, Tammy D.; Watson, Robert D.
2001-01-01
Disclosed is a method and system for actively controlling the shape of a sheet of electroactive material; the system comprising: one or more electrodes attached to the frontside of the electroactive sheet; a charged particle generator, disposed so as to direct a beam of charged particles (e.g. electrons) onto the electrode; a conductive substrate attached to the backside of the sheet; and a power supply electrically connected to the conductive substrate; whereby the sheet changes its shape in response to an electric field created across the sheet by an accumulation of electric charge within the electrode(s), relative to a potential applied to the conductive substrate. Use of multiple electrodes distributed across on the frontside ensures a uniform distribution of the charge with a single point of e-beam incidence, thereby greatly simplifying the beam scanning algorithm and raster control electronics, and reducing the problems associated with "blooming". By placing a distribution of electrodes over the front surface of a piezoelectric film (or other electroactive material), this arrangement enables improved control over the distribution of surface electric charges (e.g. electrons) by creating uniform (and possibly different) charge distributions within each individual electrode. Removal or deposition of net electric charge can be affected by controlling the secondary electron yield through manipulation of the backside electric potential with the power supply. The system can be used for actively controlling the shape of space-based deployable optics, such as adaptive mirrors and inflatable antennae.
International Nuclear Information System (INIS)
Manna, Arun K.; Pati, Swapan K.
2013-01-01
Highlights: • Stability and electronic structure of various carbon capsules are studied. • Effects of capsule’s sizes on electronic and optical properties are explored. • Changes in cohesive and formation energy and electronic gap are discussed. • Capsule’s gas storage propensity is addressed using DFT and ab initio MD. • Capsule’s optical absorptions are discussed with and without stored gas molecules. - Abstract: Structures, electronic and optical properties of carbon nanocapsules of varying sizes (length and diameter) are studied using first-principles density functional theory. Based on calculated cohesive energy, formation energy, electronic gap and extent of orbital delocalization, we examine structural stability and changes in low-energy physics of these carbon capsules. We find that both cohesive and formation energy decrease with increase in capsule’s sizes, indicating their greater structural rigidity and favorable formation feasibility. The electronic gap also decreases with increase in capsule’s sizes due to the larger electronic delocalization. The simulated optical absorption spectra show lowering of low-energy peak positions with increase in the capsule’s dimensions, consistent with the reduction in electronic gap. Additionally, we also provide an estimate of gas storage capacity for the larger carbon capsule (C 460 ) considered. We find 7.69 wt.% and 28.08 wt.% storage propensity for hydrogen and carbon dioxide gases, respectively, which clearly suggests their potential use as light storage materials
Effect of pressure on the structural properties and electronic band structure of GaSe
Energy Technology Data Exchange (ETDEWEB)
Schwarz, U.; Olguin, D.; Syassen, K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Cantarero, A. [Department of Materials Sciences, University of Valencia, 46000 Burjasot (Spain); Hanfland, M. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble (France)
2007-01-15
The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the {epsilon}-GaSe to a disordered NaCl-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered {epsilon}-phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga-Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga-Ga and Se-Se bond lengths which were not accessible to a direct experimental determination yet. Based on the optimized structural parameters, we report calculations of band gap changes of {epsilon}-GaSe under pressure. The optical response and electronic band structure of the metallic high-pressure phase of GaSe are discussed briefly. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Electronic structure and equation of state of Sm2Co17 from first-principles DFT+ U
Huang, Patrick; Butch, Nicholas P.; Jeffries, Jason R.; McCall, Scott K.
2013-03-01
Rare-earth intermetallics have important applications as permanent magnet materials, and the rational optimization of their properties would benefit greatly from guidance from ab initio modeling. However, these systems are particularly challenging for current electronic structure methods. Here, we present an ab initio study of the prototype material Sm2Co17 and related compounds, using density functional theory with a Hubbard correction for the Sm 4 f-electrons (DFT+ U method) and ultrasoft pseudopotentials. The Hubbard U parameter is derived from first principles [Cococcioni and de Gironcoli, PRB 71, 035105 (2005)], not fit to experiment. Our calculations are in good agreement with recent photoemission measurements at ambient pressure and the equation of state up to 40 GPa, thus supporting the validity of our DFT+ U model. Prepared by LLNL under Contract DE-AC52-07NA27344.
Bicanonical ab Initio Molecular Dynamics for Open Systems.
Frenzel, Johannes; Meyer, Bernd; Marx, Dominik
2017-08-08
Performing ab initio molecular dynamics simulations of open systems, where the chemical potential rather than the number of both nuclei and electrons is fixed, still is a challenge. Here, drawing on bicanonical sampling ideas introduced two decades ago by Swope and Andersen [ J. Chem. Phys. 1995 , 102 , 2851 - 2863 ] to calculate chemical potentials of liquids and solids, an ab initio simulation technique is devised, which introduces a fictitious dynamics of two superimposed but otherwise independent periodic systems including full electronic structure, such that either the chemical potential or the average fractional particle number of a specific chemical species can be kept constant. As proof of concept, we demonstrate that solvation free energies can be computed from these bicanonical ab initio simulations upon directly superimposing pure bulk water and the respective aqueous solution being the two limiting systems. The method is useful in many circumstances, for instance for studying heterogeneous catalytic processes taking place on surfaces where the chemical potential of reactants rather than their number is controlled and opens a pathway toward ab initio simulations at constant electrochemical potential.
STRUCTURAL STABILITY AND ELECTRONIC STRUCTURE OF ...
African Journals Online (AJOL)
2012-12-31
Dec 31, 2012 ... may be applications at high temperature strength and corrosion ... B2 structure, like that found in cesium-chloride (CsCl) and chemical formula RM, where R denotes a rare - earth element and M denotes a late transition metal ...
Effect of alkaline metal cations on the ionic structure of cryolite melts: Ab-initio NpT MD study
Bučko, Tomáš; Šimko, František
2018-02-01
Ab initio molecular dynamics simulations in an NpT ensemble have been performed to study the role of alkaline metal cations (Me = Li, Na, K, Rb) on the structure and vibrational properties of melts of Me-cryolites (Me3AlF6) at T = 1300 K. In all melts examined in this work, the species AlF52 - has been found to be formed at the highest abundance [from 58% (Li) to 70% (Na)] among the Al-containing anionic clusters. The concentration of clusters AlF4- increases with the size of cations while that of anions AlF63 - follows the opposite trend and it becomes negligible in the melts of the K- and Rb-cryolites. The computed percentage of the Al atoms participating in the formation of dimers Al2Fm6 -m bridged via common F atoms is significant only in the case of Li- and Na-cryolites (16% and 10%, respectively) and the formation of even larger aggregates is found to be unlikely in all four melts. The percentage of the F atoms that are not bound to Al is ˜20% in all four melts and the ions formed by Me+ and F- are found to be only short-lived. Vibrational analysis has been performed using the velocity autocorrelation functions computed for the Cartesian and selected internal coordinates describing Raman-active symmetric stretching vibrations of different AlFn species. The results of vibrational analysis allowed us to identify trends in the variation of positions and shapes of peaks corresponding to the anionic fragments AlF4-, AlF52 -, and AlF63 - with the size of cations, and these trends are found to be consistent with those deduced from the available Raman spectroscopy experiments. Our findings represent a new insight into the properties of cryolite melts, which will be useful for the interpretation of experimental data.
Casali, R. A.; Lasave, J.; Caravaca, M. A.; Koval, S.; Ponce, C. A.; Migoni, R. L.
2013-04-01
The pressure dependences of the structural, thermoelastic and vibrational properties of SnO2 in its rutile phase are studied, as well as the pressure-induced transition to a CaCl2-type phase. These studies have been performed by means of ab initio (AI) density functional theory calculations using the localized basis code SIESTA. The results are employed to develop a shell model (SM) for application in future studies of nanostructured SnO2. A good agreement of the SM results for the pressure dependences of the above properties with the ones obtained from present and previous AI calculations as well as from experiments is achieved. The transition is characterized by a rotation of the Sn-centered oxygen octahedra around the tetragonal axis through the Sn. This rotation breaks the tetragonal symmetry of the lattice and an orthorhombic distortion appears above the critical pressure Pc. A zone-center phonon of B1g symmetry in the rutile phase involves such rotation and softens on approaching Pc. It becomes an Ag mode which stabilizes with increasing pressure in the CaCl2 phase. This behavior, together with the softening of the shear modulus (C11-C12)/2 related to the orthorhombic distortion, allows a precise determination of a value for Pc. An additional determination is provided by the splitting of the basal plane lattice parameters. Both the AI and the experimentally observed softening of the B1g mode are incomplete, indicating a small discontinuity at the transition. However, all results show continuous changes in volume and lattice parameters, indicating a second-order transition. All these results indicate that there should be sufficient confidence for the future employment of the shell model.
International Nuclear Information System (INIS)
Casali, R A; Ponce, C A; Lasave, J; Koval, S; Migoni, R L; Caravaca, M A
2013-01-01
The pressure dependences of the structural, thermoelastic and vibrational properties of SnO 2 in its rutile phase are studied, as well as the pressure-induced transition to a CaCl 2 -type phase. These studies have been performed by means of ab initio (AI) density functional theory calculations using the localized basis code SIESTA. The results are employed to develop a shell model (SM) for application in future studies of nanostructured SnO 2 . A good agreement of the SM results for the pressure dependences of the above properties with the ones obtained from present and previous AI calculations as well as from experiments is achieved. The transition is characterized by a rotation of the Sn-centered oxygen octahedra around the tetragonal axis through the Sn. This rotation breaks the tetragonal symmetry of the lattice and an orthorhombic distortion appears above the critical pressure P c . A zone-center phonon of B 1g symmetry in the rutile phase involves such rotation and softens on approaching P c . It becomes an A g mode which stabilizes with increasing pressure in the CaCl 2 phase. This behavior, together with the softening of the shear modulus (C 11 −C 12 )/2 related to the orthorhombic distortion, allows a precise determination of a value for P c . An additional determination is provided by the splitting of the basal plane lattice parameters. Both the AI and the experimentally observed softening of the B 1g mode are incomplete, indicating a small discontinuity at the transition. However, all results show continuous changes in volume and lattice parameters, indicating a second-order transition. All these results indicate that there should be sufficient confidence for the future employment of the shell model. (paper)
International Nuclear Information System (INIS)
Bankura, Arindam; Chandra, Amalendu
2012-01-01
Highlights: ► A theoretical study of hydroxide ion-water clusters is carried for varying cluster size and temperature. ► The structures of OH − (H 2 O) n are found out through quantum chemical calculations for n = 4, 8, 16 and 20. ► The finite temperature behavior of the clusters is studied through ab initio dynamical simulations. ► The spectral features of OH modes (deuterated) and their dependence on hydrogen bonding states of water are discussed. ► The mechanism and kinetics of proton transfer processes in these anionic clusters are also investigated. - Abstract: We have investigated the hydration structure and dynamics of OH − (H 2 O) n clusters (n = 4, 8, 16 and 20) by means of quantum chemical and ab initio molecular dynamics calculations. Quantum chemical calculations reveal that the solvation structure of the hydroxide ion transforms from three and four-coordinated surface states to five-coordinated interior state with increase in cluster size. Several other isomeric structures with energies not very different from the most stable isomer are also found. Ab initio simulations show that the most probable configurations at higher temperatures need not be the lowest energy isomeric structure. The rates of proton transfer in these clusters are found to be slower than that in bulk water. The vibrational spectral calculations reveal distinct features for free OH (deuterated) stretch modes of water in different hydrogen bonding states. Effects of temperature on the structural and dynamical properties are also investigated for the largest cluster considered here.
Electronic structure of metallic glasses
International Nuclear Information System (INIS)
Oelhafen, P.; Lapka, R.; Gubler, U.; Krieg, J.; DasGupta, A.; Guentherodt, H.J.; Mizoguchi, T.; Hague, C.; Kuebler, J.; Nagel, S.R.
1981-01-01
This paper is organized in six sections and deals with (1) the glassy transition metal alloys, their d-band structure, the d-band shifts on alloying and their relation to the alloy heat of formation (ΔH) and the glass forming ability, (2) the glass to crystal phase transition viewed by valence band spectroscopy, (3) band structure calculations, (4) metallic glasses prepared by laser glazing, (5) glassy normal metal alloys, and (6) glassy hydrides
Phenomenology of the electron structure function
International Nuclear Information System (INIS)
Slominski, W.; Szwed, J.
2001-01-01
The advantages of introducing the electron structure function (ESF) in electron induced processes are demonstrated. Contrary to the photon structure function it is directly measured in such processes. At present energies, a simultaneous analysis of both the electron and the photon structure functions gives an important test of the experimentally applied methods. Estimates of the ESF at LEP momenta are given. At very high momenta contributions from W and Z bosons together with γ-Z interference can be observed. Predictions for the next generation of experiments are given. (orig.)
Ab Initio Study of the Structure and Stability of High-Pressure Iron-Bearing Dolomite
Solomatova, N. V.; Asimow, P. D.
2016-12-01
Carbon is subducted into the mantle primarily in the form of metasomatically calcium-enriched basaltic rock, calcified serpentinites and carbonaceous ooze, all of which often contain dolomite. End-member CaMg(CO3)2 dolomite typically breaks down upon compression into two carbonates at 5-6 GPa in the temperature range of 800-1200 K [1]. However, high-pressure X-ray diffraction experiments have recently shown that the presence of iron may be sufficient to stabilize high-pressure dolomite over single-cation carbonates above 35 GPa [2,3]. The structure and equation of state of high-pressure dolomite phases have been debated, creating a need for theoretical calculations. Using density functional theory interfaced with a genetic algorithm that predicts crystal structures (USPEX), we have found a monoclinic phase with space group C2/c. The C2/c structure has a lower energy than previously reported dolomite structures at relevant pressures. It is possible that this phase is not achieved experimentally due to a large energy barrier and a correspondingly large required volume drop, resulting in the transformation to metastable dolomite II. We calculate the equation of state of trigonal dolomite, dolomite III and monoclinic C2/c dolomite to 80 GPa with 0 and 50 mol% CaFe(CO3)2 and compare their enthalpies to single-carbonate assemblages. Although end-member C2/c CaMg(CO3)2 dolomite is not stable relative to single-cation carbonates, C2/c CaMg0.5Fe0.5(CO3)2 is preferred over single-cation carbonates at high pressures. Thus, iron-bearing C2/c dolomite may be an important host phase for carbon in slabs subducted into the lower mantle. [1] Shirasaka, M., et al. (2002) American Mineralogist, 87, 922-930. [2] Mao, Z. et al. (2011) Geophysical Research Letters, 38. [3] Merlini, M. et al. (2012) Proceedings of the National Academy of Sciences, 109, 13509-13514.
Ab-initio calculation for cation vacancy formation energy in anti-fluorite structure
Saleel, V. P. Saleel Ahammad; Chitra, D.; Veluraja, K.; Eithiraj, R. D.
2018-04-01
Lithium oxide (Li2O) has been suggested as a suitable breeder blanket material for fusion reactors. Li+ vacancies are created by neutron irradiation, forming bulk defect complex whose extra character is experimentally unclear. We present a theoretical study of Li2O using density functional theory (DFT) with a plane-wave basis set. The generalized gradient approximation (GGA) and local-density approximation (LDA) were used for exchange and correlation. Here we address the total energy for defect free, cation defect, cation vacancy and vacancy formation energy in Li2O crystal in anti-fluorite structure.
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed
2012-08-20
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Electronic structure of Pa at sign C28
International Nuclear Information System (INIS)
Zhao, Ke; Pitzer, R.M.
1995-01-01
The electronic structure of the endohedral complex Pa at sign C 28 was studied using ab initio quantum chemical methods including relativistic core potentials, gaussian double zeta basis sets, and spin-orbit configuration interaction calculations. As in U at sign C 28 , the self consistent field population analysis shows extensive mixing of Pa 6d and 5f orbitals with C π orbitals, indicating strong binding. The energy of the C 28 cage π* orbitals (e symmetry) is lower than that of the Pa 5f orbitals. The ground state has an e 1 configuration at both the SCF and CI level calculations. The lowest f 1 state is 1.68 eV and 1.70 eV above the ground state from SCF and CI calculations respectively. Previous calculations on U at sign C 28 showed that the ground state of U at sign C 28 is a π*f state instead of an f 2 state. The results for Pa at sign C 28 support that finding
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed; Anciaux-Sedrakian, Ani; Rozanska, Xavier; Klahr, Diego; Guignon, Thomas; Fleurat-Lessard, Paul
2012-01-01
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Ab initio structural and vibrational properties of GaAs diamondoids and nanocrystals
Directory of Open Access Journals (Sweden)
Mudar Ahmed Abdulsattar
2014-12-01
Full Text Available Gallium arsenide diamondoids structural and vibrational properties are investigated using density functional theory at the PBE/6-31(d level and basis including polarization functions. Variation of energy gap as these diamondoids increase in size is seen to follow confinement theory for diamondoids having nearly equiaxed dimensions. Density of energy states transforms from nearly single levels to band structure as we reach larger diamondoids. Bonds of surface hydrogen with As atoms are relatively localized and shorter than that bonded to Ga atoms. Ga-As bonds have a distribution range of values due to surface reconstruction and effect of bonding to hydrogen atoms. Experimental bulk Ga-As bond length (2.45 Å is within this distribution range. Tetrahedral and dihedral angles approach values of bulk as we go to higher diamondoids. Optical-phonon energy of larger diamondoids stabilizes at 0.037 eV (297 cm-1 compared to experimental 0.035 eV (285.2 cm-1. Ga-As force constant reaches 1.7 mDyne/Å which is comparable to Ga-Ge force constant (1.74 mDyne/Å. Hydrogen related vibrations are nearly constant and serve as a fingerprint of GaAs diamondoids while Ga-As vibrations vary with size of diamondoids.
Epitaxial graphene electronic structure and transport
International Nuclear Information System (INIS)
De Heer, Walt A; Berger, Claire; Wu Xiaosong; Sprinkle, Mike; Hu Yike; Ruan Ming; First, Phillip N; Stroscio, Joseph A; Haddon, Robert; Piot, Benjamin; Faugeras, Clement; Potemski, Marek; Moon, Jeong-Sun
2010-01-01
Since its inception in 2001, the science and technology of epitaxial graphene on hexagonal silicon carbide has matured into a major international effort and is poised to become the first carbon electronics platform. A historical perspective is presented and the unique electronic properties of single and multilayered epitaxial graphenes on electronics grade silicon carbide are reviewed. Early results on transport and the field effect in Si-face grown graphene monolayers provided proof-of-principle demonstrations. Besides monolayer epitaxial graphene, attention is given to C-face grown multilayer graphene, which consists of electronically decoupled graphene sheets. Production, structure and electronic structure are reviewed. The electronic properties, interrogated using a wide variety of surface, electrical and optical probes, are discussed. An overview is given of recent developments of several device prototypes including resistance standards based on epitaxial graphene quantum Hall devices and new ultrahigh frequency analogue epitaxial graphene amplifiers.
Thiessen, P. A.; Treder, H.-J.
Der gegenwärtige Stand der physikalischen Erkenntnis, in Sonderheit die Atomistik und die Quantentheorie, ermöglicht (in wohldefinierten Energie-Bereichen) eine ab initio-Berechnung aller physikalischen und chemischen Prozesse und Strukturen. Die Schrödinger-Gleichung erlaubt zusammen mit den Prinzipien der Quantenstatistik (Pauli-Prinzip) aus dem Planckschen Wirkungsquantum h und den atomischen Konstanten die Berechnung aller Energieumsätze, Zeitabläufe etc., die insbesondere die chemische Physik bestimmen. Die Rechenresultate gelten auch quantitativ bis auf die unvermeidliche Stochastik.Die ab initio-Berechnungen korrespondieren einerseits und sind andererseits komplementär zu den auf den Methoden der theoretischen Chemie und der klassischen Thermodynamik beruhenden Ergebnissen ex eventu. Die theoretische Behandlung ab initio führt zu mathematischen Experimenten, die die Laboratoriums-Experimente ergänzen oder auch substituieren.Translated AbstractAb initio vel ex eventuThe present state of physical knowledge, in peculiar atomistic and quantum theory, makes an ab initio calculation of all physical and chemical processes and structures possible (in well defined reaches of energy). The Schrödinger equation together with the principles of quantum statistics (Pauli principle) permits from the Planck and atomistic constants to calculate all exchanges of energy, courses of time, etc. which govern chemical physics. The calculated results are valid even quantitatively apart from the unavoidable stochastics.These ab initio calculations on the one hand correspond and are on the other complimentary to results ex eventu based on the methods of theoretical chemistry and classical thermodynamics. Theoretical treatment ab initio leads to mathematical experiments which add to or even substitute experiments in the laboratory.
Structures, Energetics, and IR Spectra of Monohydrated Inorganic Acids: Ab initio and DFT Study.
Kołaski, Maciej; Zakharenko, Aleksey A; Karthikeyan, S; Kim, Kwang S
2011-10-11
We carried out extensive calculations of diverse inorganic acids interacting with a single water molecule, through a detailed analysis of many possible conformations. The optimized structures were obtained by using density functional theory (DFT) and the second order Møller-Plesset perturbation theory (MP2). For the most stable conformers, we calculated the interaction energies at the complete basis set (CBS) limit using coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The -OH stretching harmonic and anharmonic frequencies are provided as fingerprints of characteristic conformers. The zero-point energy (ZPE) uncorrected/corrected (ΔEe/ΔE0) interaction energies and the enthalpies/free energies (ΔHr/ΔGr at room temperature and 1 bar) are reported. Various comparisons are made between many diverse inorganic acids (HmXOn where X = B/N/P/Cl/Br/I, m = 1-3, and n = 0-4) as well as other simple inorganic acids. In many cases, we find that the dispersion-driven van der Waals interactions between X in inorganic acid molecules and O in water molecules as well as the X(+)···O(-) electrostatic interactions are important.
Electronic structure of GaAs with InAs (001) monolayer
International Nuclear Information System (INIS)
Tit, N.; Peressi, M.
1995-04-01
The effect on the electronic structure of an InAs monomolecular plane inserted in bulk GaAs is investigated theoretically. The (InAs) 1 (GaAs) n (001) strained superlattice is studied via ab-initio self-consistent pseudopotential calculations. Both electrons and holes are localized nearby the inserted InAs monolayer, which therefore acts as a quantum well for all the charge carriers. The small thickness of the inserted InAs slab is responsible of high confinement energies for the charge carriers, and therefore the interband electron-heavy-hole transition energy is close to the energy gap of the bulk GaAs, in agreement with recent experimental data. (author). 18 refs, 4 figs
Ab initio study of the stability and electronic properties of wurtzite and zinc-blende BeS nanowires
Energy Technology Data Exchange (ETDEWEB)
Faraji, Somayeh [Simulation Laboratory, Department of Physics, Faculty of Science, Shahrekord University, Shahrekord (Iran, Islamic Republic of); Mokhtari, Ali, E-mail: mokhtari@sci.sku.ac.i [Simulation Laboratory, Department of Physics, Faculty of Science, Shahrekord University, Shahrekord (Iran, Islamic Republic of); Nanotechnology Research Center, Shahrekord University, Shahrekord (Iran, Islamic Republic of)
2010-07-19
In this work we study the structural stability and electronic properties of the Beryllium sulfide nanowires (NWs) in zinc-blende (ZB) and wurtzite (WZ) phases (with triangle and hexagonal cross sections), using first principle calculations within the plane-wave pseudopotential method. A phenomenological model is used to explain the role of dangling bonds in the stability of the NWs. In contrast to the bulk phase, the ZB-NWs with diameters less than 133.3 A are found to be less favorable over the WZ-NWs, in which the surface dangling bonds (DBs) on the NW facets play an important role to stabilize the NWs. Furthermore, both ZB- and WZ-NWs are predicted to be semiconductor and the values of the band gaps are dependent on the surface DBs as well as the size and shape of the NWs. Finally, we obtain atom projected density of states (PDOSs) by calculating the localized density of states on the surface atoms, as well as on the core and edge atoms.
Ab initio study of the stability and electronic properties of wurtzite and zinc-blende BeS nanowires
International Nuclear Information System (INIS)
Faraji, Somayeh; Mokhtari, Ali
2010-01-01
In this work we study the structural stability and electronic properties of the Beryllium sulfide nanowires (NWs) in zinc-blende (ZB) and wurtzite (WZ) phases (with triangle and hexagonal cross sections), using first principle calculations within the plane-wave pseudopotential method. A phenomenological model is used to explain the role of dangling bonds in the stability of the NWs. In contrast to the bulk phase, the ZB-NWs with diameters less than 133.3 A are found to be less favorable over the WZ-NWs, in which the surface dangling bonds (DBs) on the NW facets play an important role to stabilize the NWs. Furthermore, both ZB- and WZ-NWs are predicted to be semiconductor and the values of the band gaps are dependent on the surface DBs as well as the size and shape of the NWs. Finally, we obtain atom projected density of states (PDOSs) by calculating the localized density of states on the surface atoms, as well as on the core and edge atoms.
Electron conductance in curved quantum structures
DEFF Research Database (Denmark)
Willatzen, Morten; Gravesen, Jens
2010-01-01
is computationally fast and provides direct (geometrical) parameter insight as regards the determination of the electron transmission coefficient. We present, as a case study, calculations of the electron conductivity of a helically shaped quantum-wire structure and discuss the influence of the quantum......A differential-geometry analysis is employed to investigate the transmission of electrons through a curved quantum-wire structure. Although the problem is a three-dimensional spatial problem, the Schrodinger equation can be separated into three general coordinates. Hence, the proposed method...
Electronic structure of SnS deduced from photoelectron spectra and band-structure calculations
Ettema, A.R.H.F.; Groot, R.A. de; Haas, C.; Turner, T.S.
1992-01-01
SnS is a layer compound with a phase transition from a high-temperature β phase to a low-temperature α phase with a lower symmetry. Ab initio band-structure calculations are presented for both phases. The calculations show that the charge distributions in the two phases are very similar. However,
Energy Technology Data Exchange (ETDEWEB)
Sharma, Dipendra, E-mail: d-11sharma@rediffmail.com; Tiwari, S. N., E-mail: sntiwari123@rediffmail.com [Department of Physics, DDU Gorakhpur University, Gorakhpur (India); Dwivedi, M. K., E-mail: dwivedi-ji@gmail.com [Department of Physics, Banaras Hindu University, Varanasi (India)
2016-05-06
Electronic structure properties of 4-n-methoxy-4′-cyanobiphenyl, a pure nematic liquid crystal have been examined using an ab‒initio, HF/6‒31G(d,p) technique with GAMESS program. Conformational and charge distribution analysis have been carried out. MEP, HOMO and LUMO surfaces have been scanned. Ionization potential, electron affinity, electronegativity, global hardness and softness of the liquid crystal molecule have been calculated. Further, stacking, side by side and end to end interactions between a molecular pair have been evaluated. Results have been used to elucidate the physico-chemical and liquid crystalline properties of the system.
Overview of nuclear structure with electrons
International Nuclear Information System (INIS)
Geesaman, D. F.
1999-01-01
Following a broad summary of the author's view of nuclear structure in 1974, he will discuss the key elements they have learned in the past 25 years from the research at the M.I.T. Bates Linear Accelerator center and its sister electron accelerator laboratories. Electron scattering has provided the essential measurements for most of the progress. The future is bright for nuclear structure research as their ability to realistically calculate nuclear structure observables has dramatically advanced and they are increasingly able to incorporate an understanding of quantum chromodynamics into their picture of the nucleus
Augmented wave ab initio EFG calculations: some methodological warnings
International Nuclear Information System (INIS)
Errico, Leonardo A.; Renteria, Mario; Petrilli, Helena M.
2007-01-01
We discuss some accuracy aspects inherent to ab initio electronic structure calculations in the understanding of nuclear quadrupole interactions. We use the projector augmented wave method to study the electric-field gradient (EFG) at both Sn and O sites in the prototype cases SnO and SnO 2 . The term ab initio is used in the standard context of the also called first principles methods in the framework of the Density Functional Theory. As the main contributions of EFG calculations to problems in condensed matter physics are related to structural characterizations on the atomic scale, we discuss the 'state of the art' on theoretical EFG calculations and make a brief critical review on the subject, calling attention to some fundamental theoretical aspects
Augmented wave ab initio EFG calculations: some methodological warnings
Energy Technology Data Exchange (ETDEWEB)
Errico, Leonardo A. [Departamento de Fisica-IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC67 (1900) La Plata (Argentina); Renteria, Mario [Departamento de Fisica-IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC67 (1900) La Plata (Argentina); Petrilli, Helena M. [Instituto de Fisica-DFMT, Universidade de Sao Paulo, C.P. 66318, 05315-970 Sao Paulo, SP (Brazil)]. E-mail: hmpetril@macbeth.if.usp.br
2007-02-01
We discuss some accuracy aspects inherent to ab initio electronic structure calculations in the understanding of nuclear quadrupole interactions. We use the projector augmented wave method to study the electric-field gradient (EFG) at both Sn and O sites in the prototype cases SnO and SnO{sub 2}. The term ab initio is used in the standard context of the also called first principles methods in the framework of the Density Functional Theory. As the main contributions of EFG calculations to problems in condensed matter physics are related to structural characterizations on the atomic scale, we discuss the 'state of the art' on theoretical EFG calculations and make a brief critical review on the subject, calling attention to some fundamental theoretical aspects.
Energy Technology Data Exchange (ETDEWEB)
Allali, D. [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Bouhemadou, A., E-mail: a_bouhemadou@yahoo.fr [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Safi, E. Muhammad Abud Al [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Physics, Faculty of Science and Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942 (Saudi Arabia); Chegaar, M. [Department of Physics, Faculty of Science, University of Setif 1, 19000 Setif (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilson (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2014-06-15
We report ab initio density functional theory calculations of the structural, electronic and optical properties of the spinel oxides SiMg{sub 2}O{sub 4}, SiZng{sub 2}O{sub 4}, and SiCd{sub 2}O{sub 4} using the full-potential linearized augmented plane-wave method. The structural parameters calculated using both the local density and generalized gradient approximations to the exchange-correlation potential are consistent with the literature data. To calculate the electronic properties, the exchange-correlation potential is treated with various functionals, and we find that the newly developed Tran–Blaha-modified Becke–Johnson functional significantly improves the band gap. We predict a direct band gap in all of the considered SiB{sub 2}O{sub 4} compounds, and the band gaps continuously decrease as the atomic size of the B element increases. The decrease in the fundamental direct band gap (Γ–Γ) from SiMg{sub 2}O{sub 4} to SiZn{sub 2}O{sub 4} to SiCd{sub 2}O{sub 4} can be attributed to p–d mixing in the upper valence bands of SiZn{sub 2}O{sub 4} and SiCd{sub 2}O{sub 4}. The lowest conduction band is well dispersive, similar to that found for transparent conducting oxides such as ZnO. This band is mainly defined by the s and p electrons of the Si and B (B=Mg, Zn, Cd) atoms. The topmost valence band is considerably less dispersive and is defined by O-2p and B–d electrons. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band that were calculated. The frequency-dependent complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and electron energy loss function were estimated. We find that the value of the zero-frequency limit of the dielectric function ε(0) increases as the band gap decreases. The origins of the peaks and structures in the optical spectra are determined in terms of the calculated energy band structures.
Camp, Piet
1985-01-01
The 1984 Advanced Study Institute on "Electronic Structure, Dynamics and Quantum Structural Properties of Condensed Matter" took place at the Corsendonk Conference Center, close to the City of Antwerpen, from July 16 till 27, 1984. This NATO Advanced Study Institute was motivated by the research in my Institute, where, in 1971, a project was started on "ab-initio" phonon calculations in Silicon. I~ is my pleasure to thank several instances and people who made this ASI possible. First of all, the sponsor of the Institute, the NATO Scientific Committee. Next, the co-sponsors: Agfa-Gevaert, Bell Telephone Mfg. Co. N.V., C & A, Esso Belgium·, CDC Belgium, Janssens Pharmaceutica, Kredietbank and the Scientific Office of the U.S. Army. Special thanks are due to Dr. P. Van Camp and Drs. H. Nachtegaele, who, over several months, prepared the practical aspects of the ASI with the secretarial help of Mrs. R.-M. Vandekerkhof. I also like to. thank Mrs. M. Cuyvers who prepared and organized the subject and material ...
Low-energy electron scattering from CO. 2: Ab-initio study using the frame-transformation theory
Chandra, N.
1976-01-01
The Wigner-Eisenbud R matrix method has been combined with the frame transformation theory to study electron scattering from molecular systems. The R matrix, calculated at the boundary point of the molecular core radius, has been transformed to the space frame in order to continue the solution of the scattering equations in the outer region where rotational motion of the nuclei is taken into account. This procedure has been applied to a model calculation of thermal energy electron scattering from CO.
Ertürk, Esra; Gürel, Tanju
2018-05-01
We present an ab initio study of structural, elastic and vibrational properties of transition-metal disilicides NbSi2 and TaSi2. The calculations have been carried out within the density-functional theory and linear-response formalism using norm-conserving pseudopotentials and a plane-wave basis. The calculated lattice parameters, bulk moduli, and elastic constants agree well with previous theoretical and experimental results. The calculated phonon frequencies at the Brillouin zone center are in good agreement with the reported Raman spectra and provide reference values for the future infrared and neutron phonon measurements. Phonon dispersion relations, mode Grüneisen parameters, and total and partial phonon density of states are also discussed. Mode Grüneisen parameters of NbSi2 and TaSi2 at Brillouin zone center show similar trends and all values are found to be positive. From phonon dispersion relations and phonon density of states, we have found a gap around 200 cm-1 for TaSi2, where the frequencies below this gap mainly belong to Ta vibrations and frequencies above the gap is mainly related with Si vibrations. In the case of NbSi2, there is no such gap and both Nb and Si atoms contribute to the phonon density of states in an energy range of 150-270 cm-1.
Energy Technology Data Exchange (ETDEWEB)
Santhosh, M.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Priyanga, G. Sudha; Cinthia, A. Jemmy [Department of physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)
2015-06-24
Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of BeAlH{sub 5} for monoclinic crystal structures with two different types of space group namely P2{sub 1} and C{sub 2}/c. Among the considered structures monoclinic (P2{sub 1}) phase is found to be the most stable at ambient condition. The structural phase transition from monoclinic (P2{sub 1}) to monoclinic (C{sub 2}/c) phase is observed in BeAlH{sub 5}. The electronic structure reveals that this compound is insulator. The calculated elastic constants indicate that this material is mechanically stable at ambient condition.
Energy Technology Data Exchange (ETDEWEB)
Kawazoe, Yoshiyuki (Inst. for Materials Research, Tohoku Univ., Sendai (Japan)); Maruyama, Yutaka (Inst. for Materials Research, Tohoku Univ., Sendai (Japan)); Rafii-Tabar, H. (Inst. for Materials Research, Tohoku Univ., Sendai (Japan)); Ikeda, Makoto (Inst. for Materials Research, Tohoku Univ., Sendai (Japan)); Kamiyama, Hiroshi (Inst. for Materials Research, Tohoku Univ., Sendai (Japan)); Ohno, Kaoru (Inst. for Materials Research, Tohoku Univ., Sendai (Japan))
1993-04-19
The recent scanning tunnelling microscopy (STM) observations by Hashizume et al. concerning C[sub 60] buckeyballs deposited on an Si(100) surface revealed self-aligned c(4 x 4) and c(4 x 3) structures. Specific stripes on the buckeyballs in the STM images are also reported and this result proves that the buckeyballs on the Si surface are standing still, showing them to be pseudoatoms. A mixed-basis, all-electron calculation with the Car-Parinnello formalism has been introduced and performed to obtain a detailed understanding of the electronic states and dynamics of a single buckeyball. Based on the knowledge concerning a single buckeyball, a band structure calculation using the same formalism has been carried out and the experimental results have been explained clearly. A classical molecular dynamics simulation has also been performed to obtain the dynamics of the buckeyball motion on the Si surface. (orig.)
Electronic Structure of Eu6C60
Institute of Scientific and Technical Information of China (English)
WANG Xiao-Xiong; LI Hong-Nian; XU Ya-Bo; WANG Peng; ZHANG Wen-Hua; XU Fa-Qiang
2009-01-01
We study the valence band of Eu-intercalated C60 by synchrotron radiation photoelectron spectroscopy to un-derstand the ferromagnetism (FM) and the giant magnetoresistance (GMR) of Eu6C60. The results reveal the semiconducting property and the remarkable 5d6s-π hybridization. Eu-C60 bonding has both ionic and covalent contributions. No more than half the 5d6s electrons transfer from Eu to the LUMO derived band of C60, and the LUMO+1 derived band is not filled. The remaining valence electrons of Eu, together with some π (LUMO, HOMO and HOMO-1) electrons, constitute the covalent bond. The electronic structure implies that the magnetic coupling in Eu6C60 should be through the intra-atomic f-sd exchange and the medium of the π electrons. The possibility of the GMR being tunnelling magnetoresistance is ruled out.
Electronic structure of α-SrB4O7: experiment and theory
International Nuclear Information System (INIS)
Atuchin, V V; Kesler, V G; Zaitsev, A I; Molokeev, M S; Aleksandrovsky, A S; Kuzubov, A A; Ignatova, N Y
2013-01-01
The investigation of valence band structure and electronic parameters of constituent element core levels of α-SrB 4 O 7 has been carried out with x-ray photoemission spectroscopy. Optical-quality crystal α-SrB 4 O 7 has been grown by the Czochralski method. Detailed photoemission spectra of the element core levels have been recorded from the powder sample under excitation by nonmonochromatic Al Kα radiation (1486.6 eV). The band structure of α-SrB 4 O 7 has been calculated by ab initio methods and compared to XPS measurements. It has been found that the band structure of α-SrB 4 O 7 is weakly dependent on the Sr-related states. (paper)
Electronic structure and transport of a carbon chain between graphene nanoribbon leads
International Nuclear Information System (INIS)
Zhang, G P; Fang, X W; Yao, Y X; Wang, C Z; Ho, K M; Ding, Z J
2011-01-01
The electronic structure and transport property of a carbon chain between two graphene nanoribbon leads are studied using an ab initio tight-binding (TB) model and Landauer's formalism combined with a non-equilibrium Green's function. The TB Hamiltonian and overlap matrices are extracted from first-principles density functional calculations through the quasi-atomic minimal basis orbital scheme. The accuracy of the TB model is demonstrated by comparing the electronic structure from the TB model with that from first-principles density functional theory. The results of electronic transport on a carbon atomic chain connected to armchair and zigzag graphene ribbon leads, such as different transport characters near the Fermi level and at most one quantized conductance, reveal the effect of the electronic structure of the leads and the scattering from the atomic chain. In addition, bond length alternation and an interesting transmission resonance are observed in the atomic chain connected to zigzag graphene ribbon leads. Our approach provides a promising route to quantitative investigation of both the electronic structure and transport property of large systems.
Electronic structure and magnetic studies of V-doped ZnO: ab initio ...
Indian Academy of Sciences (India)
2018-05-29
May 29, 2018 ... ... (TM)-doped DMSs based on II–VI, III–V, group IV and chalcopyrite [8–12] ... expanded up to 1 = 2 in real harmonics (l is the angular momentum quantum ..... Hence, the crystal quality is deteriorated and grain size is reduced ...
Magnetic interactions and electronic structure of system: An ab-initio ...
Indian Academy of Sciences (India)
Tufan Roy
2017-06-19
Jun 19, 2017 ... 1Homi Bhaba National Institute, Training School Complex, Anushakti Nagar, Mumbai 400 094, India .... tolerance used were 10 μeV and 10 meV/Å, respec- tively. ..... calculated from the corresponding Jij values under a.
The linearly scaling 3D fragment method for large scale electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Zhao Zhengji [National Energy Research Scientific Computing Center (NERSC) (United States); Meza, Juan; Shan Hongzhang; Strohmaier, Erich; Bailey, David; Wang Linwang [Computational Research Division, Lawrence Berkeley National Laboratory (United States); Lee, Byounghak, E-mail: ZZhao@lbl.go [Physics Department, Texas State University (United States)
2009-07-01
The linearly scaling three-dimensional fragment (LS3DF) method is an O(N) ab initio electronic structure method for large-scale nano material simulations. It is a divide-and-conquer approach with a novel patching scheme that effectively cancels out the artificial boundary effects, which exist in all divide-and-conquer schemes. This method has made ab initio simulations of thousand-atom nanosystems feasible in a couple of hours, while retaining essentially the same accuracy as the direct calculation methods. The LS3DF method won the 2008 ACM Gordon Bell Prize for algorithm innovation. Our code has reached 442 Tflop/s running on 147,456 processors on the Cray XT5 (Jaguar) at OLCF, and has been run on 163,840 processors on the Blue Gene/P (Intrepid) at ALCF, and has been applied to a system containing 36,000 atoms. In this paper, we will present the recent parallel performance results of this code, and will apply the method to asymmetric CdSe/CdS core/shell nanorods, which have potential applications in electronic devices and solar cells.
Atomic and electronic structures of a-SiC:H from tight-binding molecular dynamics
Ivashchenko, V I; Shevchenko, V I; Ivashchenko, L A; Rusakov, G V
2003-01-01
The atomic and electronic properties of amorphous unhydrogenated (a-SiC) and hydrogenated (a-SiC:H) silicon carbides are studied using an sp sup 3 s sup * tight-binding force model with molecular dynamics simulations. The parameters of a repulsive pairwise potential are determined from ab initio pseudopotential calculations. Both carbides are generated from dilute vapours condensed from high temperature, with post-annealing at low temperature for a-SiC:H. A plausible model for the inter-atomic correlations and electronic states in a-SiC:H is suggested. According to this model, the formation of the amorphous network is weakly sensitive to the presence of hydrogen. Hydrogen passivates effectively only the weak bonds of threefold-coordinated atoms. Chemical ordering is very much affected by the cooling rate and the structure of the high-temperature vapour. The as-computed characteristics are in rather good agreement with the results for a-SiC and a-Si:H from ab initio calculations.
Energy Technology Data Exchange (ETDEWEB)
Ramos de Debiaggi, S., E-mail: susana.ramos@fain.uncoma.edu.ar [Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén (Argentina); Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas – CONICET-UNCo (Argentina); González Lemus, N.V. [Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén (Argentina); Deluque Toro, C. [Grupo de Nuevos Materiales, Universidad de la Guajira, Riohacha (Colombia); Fernández Guillermet, A. [CONICET - Instituto Balseiro, Centro Atómico Bariloche, Avda. Bustillo 9500, 8400 Bariloche (Argentina)
2015-01-15
Highlights: • A DFT study of the compounds involved in CALPHAD modeling of the Ni–In–Sn (hP6) phase. • Several three-sublattice compounds of Ni, In, Sn and vacancies are studied ab initio. • Structural, cohesive and thermodynamic properties and the electronic DOS are reported. • Trends in calculated properties are correlated with changes in electronic structure. • A picture of the chemical bonding trends for these s-p/d type compounds is discussed. - Abstract: The thermodynamic modeling of non-stoichiometric, multisublattice intermetallic phases using the Compound-Energy Formalism (CEF) involves the determination of parameters representing the Gibbs energy (G{sub m}) of binary compounds, the so-called “end-member compounds” (EMCs), which are often metastable or hypothetical. In current CALPHAD (i.e., “Calculation of Phase Diagrams”) work, these quantities are treated as free parameters to be determined by searching for the best fit to the available information in the optimization procedure. The general purpose of this paper is to propose a theoretical approach to the study of the EMCs which makes use of density-functional-theory (DFT) ab initio calculations. The present method is applied to the EMCs involved in the CEF modeling of the non-stoichiometric (hP6) Ni{sub 2}In-structure type phase of the Ni–In and Ni–In–Sn systems using the three-sublattice models (Ni){sub 1}(Ni,Va){sub 1}(In,Ni){sub 1} and (Ni,Va){sub 1}(Ni,Va){sub 1}(In,Ni,Sn){sub 1}, respectively. By means of systematic ab initio projected augmented waves (PAW) calculations using the VASP code we study the EMCs involved in the CEF formulations of the G{sub m} for this phase in the binary and the ternary systems. Specifically, we study the twelve EMCs corresponding to the following sublattice occupations: (Ni){sub 1}(Ni){sub 1}(In){sub 1}, which is usually described as Ni:Ni:In (i.e., a compound with formula “Ni{sub 2}In”), Ni:Ni:Ni (i.e., “Ni{sub 3}”), Ni:Ni:Sn (
International Nuclear Information System (INIS)
Ramos de Debiaggi, S.; González Lemus, N.V.; Deluque Toro, C.; Fernández Guillermet, A.
2015-01-01
Highlights: • A DFT study of the compounds involved in CALPHAD modeling of the Ni–In–Sn (hP6) phase. • Several three-sublattice compounds of Ni, In, Sn and vacancies are studied ab initio. • Structural, cohesive and thermodynamic properties and the electronic DOS are reported. • Trends in calculated properties are correlated with changes in electronic structure. • A picture of the chemical bonding trends for these s-p/d type compounds is discussed. - Abstract: The thermodynamic modeling of non-stoichiometric, multisublattice intermetallic phases using the Compound-Energy Formalism (CEF) involves the determination of parameters representing the Gibbs energy (G m ) of binary compounds, the so-called “end-member compounds” (EMCs), which are often metastable or hypothetical. In current CALPHAD (i.e., “Calculation of Phase Diagrams”) work, these quantities are treated as free parameters to be determined by searching for the best fit to the available information in the optimization procedure. The general purpose of this paper is to propose a theoretical approach to the study of the EMCs which makes use of density-functional-theory (DFT) ab initio calculations. The present method is applied to the EMCs involved in the CEF modeling of the non-stoichiometric (hP6) Ni 2 In-structure type phase of the Ni–In and Ni–In–Sn systems using the three-sublattice models (Ni) 1 (Ni,Va) 1 (In,Ni) 1 and (Ni,Va) 1 (Ni,Va) 1 (In,Ni,Sn) 1 , respectively. By means of systematic ab initio projected augmented waves (PAW) calculations using the VASP code we study the EMCs involved in the CEF formulations of the G m for this phase in the binary and the ternary systems. Specifically, we study the twelve EMCs corresponding to the following sublattice occupations: (Ni) 1 (Ni) 1 (In) 1 , which is usually described as Ni:Ni:In (i.e., a compound with formula “Ni 2 In”), Ni:Ni:Ni (i.e., “Ni 3 ”), Ni:Ni:Sn (“Ni 2 Sn”), Ni:Va:In (i.e., “NiIn”), Ni:Va:Ni (i
Liu, Lihong; Fang, Wei-Hai; Long, Run; Prezhdo, Oleg V
2018-03-01
Nonradiative electron-hole recombination plays a key role in determining photon conversion efficiencies in solar cells. Experiments demonstrate significant reduction in the recombination rate upon passivation of methylammonium lead iodide perovskite with Lewis base molecules. Using nonadiabatic molecular dynamics combined with time-domain density functional theory, we find that the nonradiative charge recombination is decelerated by an order of magnitude upon adsorption of the molecules. Thiophene acts by the traditional passivation mechanism, forcing electron density away from the surface. In contrast, pyridine localizes the electron at the surface while leaving it energetically near the conduction band edge. This is because pyridine creates a stronger coordinative bond with a lead atom of the perovskite and has a lower energy unoccupied orbital compared with thiophene due to the more electronegative nitrogen atom relative to thiophene's sulfur. Both molecules reduce two-fold the nonadiabatic coupling and electronic coherence time. A broad range of vibrational modes couple to the electronic subsystem, arising from inorganic and organic components. The simulations reveal the atomistic mechanisms underlying the enhancement of the excited-state lifetime achieved by the perovskite passivation, rationalize the experimental results, and advance our understanding of charge-phonon dynamics in perovskite solar cells.
Atomic and electronic structures of novel silicon surface structures
Energy Technology Data Exchange (ETDEWEB)
Terry, J.H. Jr.
1997-03-01
The modification of silicon surfaces is presently of great interest to the semiconductor device community. Three distinct areas are the subject of inquiry: first, modification of the silicon electronic structure; second, passivation of the silicon surface; and third, functionalization of the silicon surface. It is believed that surface modification of these types will lead to useful electronic devices by pairing these modified surfaces with traditional silicon device technology. Therefore, silicon wafers with modified electronic structure (light-emitting porous silicon), passivated surfaces (H-Si(111), Cl-Si(111), Alkyl-Si(111)), and functionalized surfaces (Alkyl-Si(111)) have been studied in order to determine the fundamental properties of surface geometry and electronic structure using synchrotron radiation-based techniques.
Energy Technology Data Exchange (ETDEWEB)
Fang, C.M.; Metselaar, R.; Hintzen, H.T.; With, G. de [Eindhoven Univ. of Technology (Netherlands). Lab. of Solid State and Materials Chemistry
2002-07-01
Theoretical simulations using density functional theory (DFT) within ab initio total-energy and molecular-dynamics method have been performed for several oxynitride materials. Examples dealt with are compounds in the Ta-O-N, Si-O-N and Al-O-N systems. Random or partially ordered distributions of the oxygen and nitrogen ions as well as other structural defects can be predicted very well by these methods. Local structure relaxation and its influence on the electronic properties are addressed. (orig.)
International Nuclear Information System (INIS)
Campetella, M.; Caminiti, R.; Bencivenni, L.; Gontrani, L.; Bovi, D.; Guidoni, L.
2016-01-01
In this work we report an analysis of the bulk phase of 2-methoxyethylammonium nitrate based on ab initio molecular dynamics. The structural and dynamical features of the ionic liquid have been characterized and the computational findings have been compared with the experimental X-ray diffraction patterns, with infrared spectroscopy data, and with the results obtained from molecular dynamics simulations. The experimental infrared spectrum was interpreted with the support of calculated vibrational density of states as well as harmonic frequency calculations of selected gas phase clusters. Particular attention was addressed to the high frequency region of the cation (ω > 2000 cm −1 ), where the vibrational motions involve the NH 3 + group responsible for hydrogen bond formation, and to the frequency range 1200-1400 cm −1 where the antisymmetric stretching mode (ν 3 ) of nitrate is found. Its multiple absorption lines in the liquid arise from the removal of the degeneracy present in the D 3h symmetry of the isolated ion. Our ab initio molecular dynamics leads to a rationalization of the frequency shifts and splittings, which are inextricably related to the structural modifications induced by a hydrogen bonding environment. The DFT calculations lead to an inhomogeneous environment.
Energy Technology Data Exchange (ETDEWEB)
Campetella, M.; Caminiti, R.; Bencivenni, L.; Gontrani, L., E-mail: lorenzo.gontrani@uniroma1.it [Dipartimento di Chimica, Università di Roma, “La Sapienza,” P. le Aldo Moro 5, I-00185 Roma (Italy); Bovi, D. [Dipartimento di Fisica, Università di Roma, “La Sapienza,” P. le Aldo Moro 5, I-00185 Roma (Italy); Guidoni, L. [Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell’Aquila, Via Vetoio, Coppito, I-67100 L’Aquila (Italy)
2016-07-14
In this work we report an analysis of the bulk phase of 2-methoxyethylammonium nitrate based on ab initio molecular dynamics. The structural and dynamical features of the ionic liquid have been characterized and the computational findings have been compared with the experimental X-ray diffraction patterns, with infrared spectroscopy data, and with the results obtained from molecular dynamics simulations. The experimental infrared spectrum was interpreted with the support of calculated vibrational density of states as well as harmonic frequency calculations of selected gas phase clusters. Particular attention was addressed to the high frequency region of the cation (ω > 2000 cm{sup −1}), where the vibrational motions involve the NH{sub 3}+ group responsible for hydrogen bond formation, and to the frequency range 1200-1400 cm{sup −1} where the antisymmetric stretching mode (ν{sub 3}) of nitrate is found. Its multiple absorption lines in the liquid arise from the removal of the degeneracy present in the D{sub 3h} symmetry of the isolated ion. Our ab initio molecular dynamics leads to a rationalization of the frequency shifts and splittings, which are inextricably related to the structural modifications induced by a hydrogen bonding environment. The DFT calculations lead to an inhomogeneous environment.
International Nuclear Information System (INIS)
Charkin, O.P.; Klimenko, N.M.; MakKi, M.L.; Shlojer, P.R.
1999-01-01
Ab initio calculations of potential energy surfaces in neighborhood of key structures of non rigid dimer molecules of lithium salts of (LiAB) 2 type - (LiBO) 2 , (LiAlO) 2 , (LiBS) 2 , (LiAlS) 2 , (LiCN) 2 , (LiSiN) 2 , (LiCP) 2 , (LiSiP) 2 - with 20 valent electrons are done in the framework of MP2/6-31G8//HF/6-31G* + ZPE(HF/6-31G*) and MP4SDTQ/6-31G*//MP2/6-31G* + ZPE(MP2/6-31G*) approximations. Totality of low-lying isomers containing four- and six-membered cycles with lithium bridges is localized. It is shown that for all cycles not rigidity to high deformation of angles in the case of low energy changes is characterized. Equilibrium geometrical parameters, relative energy and energy of isomer decomposition, frequency and intensities of normal vibrations are determined [ru
Srivastava, Anubha; Tandon, Poonam; Jain, Sudha; Asthana, B P
2011-12-15
(+)-Bicuculline (hereinafter referred to as bicuculline), a phthalide isoquinoline alkaloid is of current interest as an antagonist of gamma-aminobutyric acid (GABA). Its inhibitor properties have been studied through molecular electrostatic potential (MEP) mapping of this molecule and GABA receptor. The hot site on the potential surface of bicuculline, which is also isosteric with GABA receptor, has been used to interpret the inhibitor property. A systematic quantum chemical study of the possible conformations, their relative stabilities, FT-Raman, FT-IR and UV-vis spectroscopic analysis of bicuculline has been reported. The optimized geometries, wavenumber and intensity of the vibrational bands of all the conformers of bicuculline have been calculated using ab initio Hartree-Fock (HF) and density functional theory (DFT) employing B3LYP functional and 6-311G(d,p) basis set. Mulliken atomic charges, HOMO-LUMO gap ΔE, ionization potential, dipole moments and total energy have also been obtained for the optimized geometries of both the molecules. TD-DFT method is used to calculate the electronic absorption parameters in gas phase as well as in solvent environment using integral equation formalism-polarizable continuum model (IEF-PCM) employing 6-31G basis set and the results thus obtained are compared with the UV absorption spectra. The combination of experimental and calculated results provides an insight into the structural and vibrational spectroscopic properties of bicuculline. Copyright © 2011 Elsevier B.V. All rights reserved.
The electronic structure of molecules by a many-body approach. Pt. 1
International Nuclear Information System (INIS)
Niessen, W. von; Cederbaum, L.S.; Kraemer, W.P.
1976-01-01
The ionization potentials of benzene are studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the one-particle approximation. The calculations confirm the assignment of the photoelectron spectrum experimentally proposed by Jonsson and Lindholm: 1esub(1g)(π), 2esub(2g), 1asub(2u)(π), 2esub(1u), 1bsub(2u), 1bsub(1u), 2asub(1g), 1esub(2g) in order of increasing binding energy. To definitely establish the ordering of the ionization potentials in the second band, which has been very controversial, the corresponding vibrational structure has been calculated. A number of one-electron properties are calculated in the one-particle approximation and compared to experimental work and other theoretical calculations. (orig.) [de
Structural changes induced by electron irradiation
International Nuclear Information System (INIS)
Koike, J.; Pedraza, D.F.
1993-01-01
Highly oriented pyrolytic graphite was irradiated at room temperature with 300 kV electrons. Transmission electron microscopy and electron energy loss spectroscopy were employed to study the structural changes produced by irradiation. The occurrence of a continuous ring intensity in the selected area diffraction (SAD) pattern obtained on a specimen irradiated with the electron beam parallel to the c-crystallographic axis indicated that microstructural changes had occurred. However, from the SAD pattern obtained for the specimens tilted relative to the irradiation direction, it was found that up to a fluence of 1.1x10 27 e/m 2 graphite remained crystalline. An SAD pattern of a specimen irradiated with the electron beam perpendicular to the c-axis confirmed the persistence of crystalline order. High resolution electron microscopy showed that ordering along the c-axis direction remained. A density reduction of 8.9% due to irradiation was determined from the plasmon frequency shift. A qualitative model is proposed to explain these observations. A new determination of the threshold displacement energy, Ed, of carbon atoms in graphite was done by examining the appearance of a continuous ring in the SAD pattern at various electron energies. A value of 30 eV was obtained whether the incident electron beam was parallel or perpendicular to the c-axis, demonstrating that Ed is independent of the displacement direction
Ha, T.-K.; Günthard, H. H.
1989-07-01
Structural parameters like bond length, bond angles, etc. and harmonic and anharmonic potential coefficients of molecules with internal rotation, inversion or puckering modes are generally assumed to vary with the large amplitude internal coordinates in a concerted manner (relaxation). Taking the coordinate vectors of the nuclear configuration of semirigid molecules with relaxation (SRMRs) as functions of relaxing structural parameters and finite amplitude internal coordinate, the isometric group of SRMRs is discussed and the irreducible representations of the latter are shown to classify into engendered and nonengendered ones. On this basis a concept of equivalent sets of nuclei SRMRs is introduced and an analytical expression is derived which defines the most general functional form of relaxation increments of all common types of structural parameters compatible with isometric symmetry. This formula is shown to be a close analog of an analytical expression defining the transformations induced by the isometric group of infinitesimal internal coordinates associated with typical structural parameters. Furthermore analogous formulae are given for the most general form of the relaxation of harmonic potential coefficients as a function of finite internal coordinates. The general relations are illustrated by ab initio calculations for 1,2-difluoroethane at the MP4/DZP//HF/4-31G* level for twelve values of the dihedral angle including complete structure optimization. The potential to internal rotation is found to be in essential agreement with experimentally derived data. For a complete set of ab initio structural parameters the associated relaxation increments are represented as Fourier series, which are shown to confirm the form predicted by the general formula and the isometric group of 1,2-difluoroethane. Depending on type of the structural parameters (bond length, bond angles, etc.), the associated relaxation increments appear to follow some simple rules. Similarly
Structural stability and electronic structure of YCu ductile ...
African Journals Online (AJOL)
We investigate the structural, elastic and electronic properties of cubic YCu intermetallic compound. Which crystallize in the CsCl- B2 type structure, the investigated using the first principle full potential linearized augmented plane wave method (FP-LAPW) within density functional Theory (DFT). We used generalized ...
Electronic structure of Ni-- and Ni2--ethylene cluster complexes
International Nuclear Information System (INIS)
Basch, H.; Newton, M.D.; Moskowitz, J.W.
1978-01-01
The electronic structure of metal cluster--ethylene complexes has been investigated by carrying out ab initio bonding pair-correlated, self-consistent field, and configuration interaction (CI) calculations on the NiC 2 H 4 and Ni 2 C 2 H 4 species. The π-NiC 2 H 4 and π-Ni 2 C 2 H 4 cluster complexes are found to be bound, the former only with CI, while disigma-Ni 2 C 2 H 4 has only a repulsive Ni 2 --C 2 H 4 ground state potential curve. The bonding in the π-type cluster complexes can be described as follows: The metal atom configuration is 3d 9 4s 1 with the 4s hybridized (by the metal 4p) away from the ethylene molecule, thereby allowing the π orbital to form a dative sigma bond with the metal atom. The bonding interaction is promoted by the presence of a second nickel atom behind the first one, leading to a 4s orbital electron deficiency of the bonded nickel atom and thus making this nickel atom a better electron acceptor. Back donation from the occupied metal 3d into the ethylene π* molecular orbital also takes place to some extent, and thus both features of the classical Dewar--Chatt--Duncanson model are observed. The π-Ni 2 C 2 H 4 species is analyzed in terms of the addition of a bare nickel atom to a π-NiC 2 H 4 cluster complex, with concomitant stabilization of the orbitals of the bonded nickel atom. A study of the excited electronic states of π-NiC 2 H 4 shows that low-lying 4s→π* and 3d→π* (M→L) charge transfer transitions are predicted. The former is not observed experimentally, probably due to the diffuse nature of the 4s orbital. The relationship between small cluster--ethylene complex systems and ethylene chemisorption on a nickel metal surface is discussed
Push-pull alkenes: structure and p-electron distribution
Directory of Open Access Journals (Sweden)
ERICH KLEINPETER
2006-01-01
Full Text Available Push-pull alkenes are substituted alkenes with one or two electron-donating substituents on one end of C=C double bond and with one or two electron-accepting substituents at the other end. Allowance for p-electron delocalization leads to the central C=C double bond becoming ever more polarized and with rising push-pull character, the p-bond order of this double bond is reduced and, conversely, the corresponding p-bond orders of the C–Don and C–Acc bonds are accordingly increased. This push-pull effect is of decisive influence on both the dynamic behavior and the chemical reactivity of this class of compounds and thus it is of considerable interest to both determine and to quantify the inherent push-pull effect. Previously, the barriers to rotation about the C=C, C–Don and/or C–Acc partial double bonds (DG±, as determined by dynamic NMR spectroscopy or the 13C chemical shift difference of the polarized C=C partial double bond (DdC=C were employed for this purpose. However, these parameters can have serious limitations, viz. the barriers can be immeasurable on the NMR timescale (either by being too high or too low; heavily-biased conformers are present, etc. or DdC=C behaves in a non-additive manner with respect to the combination of the four substituents. Hence, a general parameter to quantify the push-pull effect is not yet available. Ab initio MO calculations on a collection of compounds, together with NBO analysis, provided valuable information on the structure, bond energies, electron occupancies and bonding/antibonding interactions. In addition to DG±C=C (either experimentally determined or theoretically calculated and DdC=C, the bond length of the C=C partial double bond was also examined and it proved to be a reliable parameter to quantify the push-pull effect. Equally so, the quotient of the occupation numbers of the antibonding andbonding p orbitals of the central C=C partial double bond ( p*C=C/ pC=C could also be employed for
Virtual synthesis of crystals using ab initio MD: Case study on LiFePO4
Mishra, S. B.; Nanda, B. R. K.
2017-05-01
Molecular dynamics simulation technique is fairly successful in studying the structural aspects and dynamics of fluids. Here we study the ability of ab initio molecular dynamics (ab initio MD) to carry out virtual experiments to synthesize new crystalline materials and to predict their structures. For this purpose the olivine phosphate LiFePO4 (LFPO) is used as an example. As transition metal oxides in general are stabilized with layered geometry, we carried out ab initio MD simulations over a hypothetical layered configuration consisting of alternate LiPO2 and FeO2 layers. With intermittent steps of electron minimization, the resulted equilibrium lattice consist of PO4 tetrahedra and distorted Fe-O complexes similar to the one observed in the experimental lattice.
Li, Miao-Miao; Li, Jin-Feng; Bai, Hongcun; Sun, Yin-Yin; Li, Jian-Li; Yin, Bing
2015-08-21
The regulation of the electronic properties of organic molecules induced by polynuclear superhalogens is theoretically explored here for sixteen composite structures. It is clearly indicated by the higher vertical electron detachment energy (VDE) that polynuclear superhalogens are more effective in regulating the electronic properties than mononuclear structures. However, this enhanced regulation is not only determined by superhalogens themselves but also related to the distribution of the extra electron of the final composites. The composites, in which the extra electron is mainly aggregated into the superhalogen moiety, will possess higher VDE values, as reported in the case of C1', 7.12 eV at the CCSD(T) level. This is probably due to the fact that, compared with organic molecules, superhalogens possess stronger attraction towards the extra electron and thus should lead to lower energies of the extra electrons and to higher VDE values eventually. Compared with CCSD(T), the Outer Valence Green's Function (OVGF) method fails completely for composite structures containing Cl atoms, while MP2 results are generally consistent in terms of the relative order of VDEs. Actually if the extra electron distribution of the systems could be approximated by the HOMO, the results at the OVGF level will be consistent with the CCSD(T) results. Conversely, the difference in VDEs between OVGF and CCSD(T) is significantly large. Besides superhalogen properties, the structures, relative stabilities and thermodynamic stabilities with respect to various fragmentation channels were also investigated for all the composite structures.
Electron acoustic nonlinear structures in planetary magnetospheres
Shah, K. H.; Qureshi, M. N. S.; Masood, W.; Shah, H. A.
2018-04-01
In this paper, we have studied linear and nonlinear propagation of electron acoustic waves (EAWs) comprising cold and hot populations in which the ions form the neutralizing background. The hot electrons have been assumed to follow the generalized ( r , q ) distribution which has the advantage that it mimics most of the distribution functions observed in space plasmas. Interestingly, it has been found that unlike Maxwellian and kappa distributions, the electron acoustic waves admit not only rarefactive structures but also allow the formation of compressive solitary structures for generalized ( r , q ) distribution. It has been found that the flatness parameter r , tail parameter q , and the nonlinear propagation velocity u affect the propagation characteristics of nonlinear EAWs. Using the plasmas parameters, typically found in Saturn's magnetosphere and the Earth's auroral region, where two populations of electrons and electron acoustic solitary waves (EASWs) have been observed, we have given an estimate of the scale lengths over which these nonlinear waves are expected to form and how the size of these structures would vary with the change in the shape of the distribution function and with the change of the plasma parameters.
DEFF Research Database (Denmark)
Zeng, Zhenhua; Hansen, Martin Hangaard; Greeley, Jeffrey Philip
2014-01-01
. In this paper we present a scheme to determine the metal–oxide interface structure at a given set of these environmental parameters based on quantum chemical calculations. As an illustration we determine the structure of a Ni-YSZ anode as a function of electrode potential at 0 and 1000 K. We further describe...
Self-consistent electronic structure of disordered Fe/sub 0.65/Ni/sub 0.35/
International Nuclear Information System (INIS)
Johnson, D.D.; Pinski, F.J.; Stocks, G.M.
1985-01-01
We present the results of the first ab initio calculation of the electronic structure of the disordered alloy Fe/sub 0.65/Ni/sub 0.35/. The calculation is based on the multiple-scattering coherent-potential approach (KKR-CPA) and is fully self-consistent and spin polarized. Magnetic effects are included within local-spin-density functional theory using the exchange-correlation function of Vosko--Wilk--Nusair. The most striking feature of the calculation is that electrons of different spins experience different degrees of disorder. The minority spin electrons see a very large disorder, whereas the majority spin electrons see little disorder. Consequently, the minority spin density of states is smooth compared to the very structured majority spin density of states. This difference is due to a subtle balance between exchange splitting and charge neutrality
Structure of conduction electrons on polysilanes
Energy Technology Data Exchange (ETDEWEB)
Ichikawa, Tsuneki [Hokkaido Univ., Sapporo (Japan); Kumagai, Jun
1998-10-01
The orbital structures of conduction electrons on permethylated oligosilane, Si{sub 2n}(CH{sub 3}){sub 2n+2}(n = 2 - 8), and poly(cyclohexylmethylsilane) have been determined by the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms. Quantum-chemical calculations suggest that Anderson localization due to fluctuation of {sigma} conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole. (author)
Electronic structure of Fe-based superconductors
Indian Academy of Sciences (India)
Abstract. Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the dominant ...
Electronic structure of Fe-based superconductors
Indian Academy of Sciences (India)
2015-05-29
May 29, 2015 ... Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the ...