bluuebunny/crossref_metadata_2025_split huggingface dataset:
A complex defect studied through DFT: The Fe3–O2− pair in KMgF3
Authors: Aramburu J. A. , García‐Lastra J. M. , Barriuso M. T. , Moreno M. 
Published: December 2002

AbstractElectron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopies performed by different authors in KMgF3, KZnF3, and RbCdF3 have detected a strongly axial Fe3+ center that was tentatively assigned to a FeF5O4− complex. The current work is devoted to exploring the properties of the FeF5O4− center (C4V symmetry) in KMgF3 by means of density functional calculations. The equilibrium distance between Fe3+ and O2− (1.83 Å) is found to be only ∼10% higher than that computed for the Fe3+–O2− pair in vacuo (1.63 Å), but ∼25 pm smaller than that corresponding to FeO units. These data together with the charge transferred onto the oxygen in the antibonding a (≈3z2 − r2) orbital reveals the formation of a Fe3+–O2− pair inside the KMgF3 lattice. In comparison with FeF the substitution of a F− ion by an O2− one is found to produce an increase of distances between Fe3+ and the four equatorial (Req) and apical (Rax) F− ligands equal to 10 pm and 17 pm, respectively. The current calculations reasonably account for the experimental fingerprint of this center, where the isotropic superhyperfine constant for the equatorial fluorines (As(eq)) is found to be about twice that for the apical fluorine (As(ax)). This huge difference between As(eq) and As(ax) cannot be explained on the basis of the equilibrium Req and Rax values and the law relating As to the metal–ligand distance, R, for the octahedral FeF unit. This salient feature stresses that laws valid for a given kind of complex cannot be transferred to complexes with lower symmetry. Along this line, the current results cast doubts on the conclusions previously reached using the empirical superposition model. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
First‐principles elastic properties of BAs
Authors: Herrera‐Cabrera M. J. , Rodríguez‐Hernández P. , Muñoz A. 
Published: December 2002

AbstractWe used an ab initio total energy pseudopotential technique within the density functional theory in the local‐density approximation to determine the full set of first‐order elastic constants of BAs, which have not been established experimentally. We also calculated the bulk modulus, the optical phonon frequency at the Γ point, and we present a study of the electronic band structure. Finally we also determined the pressure dependence of the elastic constants Cij. Due to the absence of the experimental data our results can be considered as reliable predictions of the elastic moduli and the pressure derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
DFT study of the Jahn–Teller impurity Rh2+ in octahedral symmetry
Authors: Barriuso M. T. , García Fernández P. , Aramburu J. A. , Moreno M. 
Published: December 2002

AbstractDensity functional calculations on clusters involving up to 87 atoms have been carried out for exploring the Jahn–Teller effect in NaCl: Rh2+. Due to the flexibility of density functional theory (DFT) methodology, calculations have first been performed for a ground state described by the (3z2 − r2)0.5(x2 − y2)0.5 configuration at different values of the Qθ(≈3z2 − r2) distortion. This electronic configuration allows one to extract the angular frequency, ωE, and anharmonic parameter, A3, corresponding to a hypothetical Rh2+ ion without orbital degeneracy. The calculation on an 87‐atom cluster indicates that ligands have undergone a 10% inward relaxation whereas the first Na+ ions along <100> directions experience a small outward relaxation. The latter fact is related to the additional positive charge created through the Na+ → Rh2+ substitution. Calculations at different Qθ(≈3z2 − r2) distortions for a ground state described by (3z2 − r2)1 and (x2 − y2)1 configurations have also been carried out and reveal that: (1) the energy minimum for the former electronic configuration corresponds to an elongated octahedron lying ≈200 cm−1 below the minimum associated with (x2 − y2)1 configuration displaying a compressed D4h geometry; (2) the calculated ratio EJT/ℏωE where EJT is the Jahn–Teller energy is found to be equal to 7.5, stressing that the Jahn–Teller effect in NaCl: Rh2+ is strong. These conclusions concur with available experimental findings. The current calculations reasonably account for the two crystal‐field transitions and the charge transfer band detected through magnetic circular dichroism up to 4.1 eV. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 2003
DFT‐based solution to the gap problem of antiferromagnetic transition metal oxides and parent compounds of high‐Tc superconductors
Authors: Fritsche L. , Pérez‐Jiménez A. J. , Reinert T. 
Published: December 2002

AbstractCurrently used approximations to the exchange‐correlation potential in density functional theory (DFT) are known to fail in describing the properties of certain compounds, of which we discuss here only two examples: CoO and stoichiometric La2CuO4. Both materials are insulating and antiferromagnetic. A DFT calculation on CoO yields antiferromagnetic order, but Co‐associated magnetic moments that are by ∼1 μB smaller than the experimental value, and one obtains the electronic structure of a metal. The latter applies also to La2CuO4, and, in contrast to the experiment, the calculation does not even yield nonzero moments associated with the Cu atoms. We exploit the fact that approximate exchange‐correlation potentials lead necessarily to spin‐dependent densities that differ from the exact ones. We therefore derive modified Kohn–Sham (KS) equations in which the effective potentials depend on the exact spin densities rather than on the standard KS densities. If the latter are modified by adding small (spin‐up, spin‐down) portions that individually integrate to zero within the lattice unit cell and do not change the total charge density, the inconsistencies with the experiment can be removed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Exchange‐correlation energies and correlation holes for some two‐ and four‐electron atoms along a nonlinear adiabatic connection in density functional theory
Authors: Pollet R. , Colonna F. , Leininger T. , Stoll H. , Werner H.‐J. , Savin A. 
Published: December 2002

AbstractThe adiabatic connection procedure of density functional theory has been applied to two‐ and four‐electron atomic systems by following a nonlinear path that leads from the noninteracting Kohn–Sham reference system to the physical one. We have calculated the exchange and correlation energies as the interaction strength is increased, as well as the densities of the corresponding correlation holes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
MIKA: Multigrid‐based program package for electronic structure calculations
Authors: Torsti T. , Heiskanen M. , Puska M. J. , Nieminen R. M. 
Published: December 2002

AbstractA general real‐space multigrid‐based program package MIKA (Multigrid Instead of the K‐spAce) for the self‐consistent solution of the Kohn–Sham equations appearing in the state‐of‐the‐art electronic structure calculations is described. The most important part of the method is the multigrid solver for the Schrödinger equation. Our choice is the Rayleigh quotient multigrid method (RQMG), which applies directly to the minimization of the Rayleigh quotient on the finest level. Coarse correction grids can be used because there is in principle no need to represent the states on the coarse levels. The RQMG method is generalized for the simultaneous solution of all the states of the system using a penalty functional to keep the states orthogonal. Special care has been taken to optimize the iterations toward the self‐consistency and run the code in parallel computer architectures. The scheme has been implemented in multiple geometries. We show examples from electronic structure calculations employing nonlocal pseudopotentials and/or the jellium model. The RQMG solver is also applied for the calculation of positron states in solids. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Thickness‐dependent interface magnetism of Fe/Cr/Fe trilayers
Authors: Man'kovsky S. V. , Baldomir D. , Pereiro M. 
Published: December 2002

AbstractElectronic structure and magnetic properties of FeN/Cr3/FeN bcc(100) trilayers (N is the number of atomic layers) are studied on the basis of ab initio calculations performed within the framework of the density functional theory in the local spin density approximation, using the full‐potential LAPW method in slab geometry. According to our calculations, the magnetic moment of a surface Fe layer increases monotonically from 2.45 μB for N = 1 to 2.92 μB for N = 3 and practically does not change at further increase of the Fe film thickness. However, the magnetic moment in the interface Fe layer changes nonmonotonically with the Fe film thickness increase and is close to the surface value at N = 5 and 7. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Properties of simple metals beyond the local density approximation of density functional theory
Authors: Almeida L. M. , Fiolhais Carlos , Causà M. 
Published: December 2002

AbstractWe calculated lattice parameters, binding energies, bulk moduli, and phase stabilities of some simple metals: Li, Be, Na, Mg, and Al. Our ab initio all‐electron calculations were done within the framework of density functional theory using the Crystal‐98 program. The accuracy of different functionals for exchange and correlation energies that go beyond the local density approximation (LDA) was tested. The recent metageneralized gradient approximation proposed from Perdew et al. (Phys Rev Lett 1999, 82, 2544) gives lattice parameters that are better than the LDA values but not always better than the results of generalized gradient approximation. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Realizations of the noninteracting kinetic energy functional enhancement factor through local‐scaling transformations: Atoms
Authors: Ludeña Eduardo V. , Karasiev Valentin V. , Echevarría Lorenzo 
Published: December 2002

AbstractWithin the framework of the local‐scaling version of density functional theory, we deal with the problem of constructing approximate forms for the noninteracting kinetic energy functional Ts[ρ]. For this purpose, we resort to density‐dependent orbitals generated by means of local‐scaling transformations. We examine the use of different types of initial orbital sets for the generation of the density‐dependent orbitals and, in particular, analyze the realization of the enhancement factor in terms of locally scaled plane waves, orthogonal polynomials (Laguerre), and generalized Slater‐type orbitals. Application to the Na and Al atoms shows the feasibility of representing the enhancement factor in closed form, in particular when generalized Slater‐type orbitals are used. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Is the vanadium(001) surface magnetic? Pseudopotential toward all‐electron calculations
Authors: Robles R. , Izquierdo J. , Vega A. , Balbás L. C. 
Published: December 2002

AbstractThe spin polarization of the vanadium(001) surface is studied by means of first‐principles generalized gradient approximation (GGA) calculations within the linear combination of atomic orbitals (LCAO) code Siesta and the norm‐conserving pseudopotentials of Troullier–Martins. Whereas the conventional valence 4s23d3 pseudopotential, including nonlinear core corrections (NLCC), leads to a high surface polarization for the 7‐, 9‐, and 15‐layer (001) films of V (with and without relaxation), treating explicitly as valence electrons, the semicore 3p6 state we obtain is a considerable reduction of the magnetic moment at the surface, which became nonmagnetic for the relaxed 15‐layer film, in agreement with recent all‐electron GGA first‐principles calculations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Self‐consistent solution of Dyson's equation up to second order for closed‐ and open‐shell atomic systems
Authors: Peirs K. , Van Neck D. , Waroquier M. 
Published: December 2002

AbstractGreen's function techniques offer new methods based upon perturbation theory to study many‐body systems. The computational cost in these schemes is substantially higher than in density functional theory (DFT), but they offer a clear picture of the nature of correlations included in the calculations. In this way, a connection between the Green's function scheme and DFT can learn more about the underlying mechanisms of the latter. Therefore, we need the correlated density of some carefully selected systems. In this work, a numerical scheme is presented to solve the Dyson equation up to second order self‐consistently for a few closed‐shell (He, Be, Ne, Mg, and Ar) and open‐shell (B, C, N, O, and F) atoms in coordinate space. A detailed discussion is held on the reproduction of total binding energies, ionization energies, electron affinities, and spectral strength distributions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
First principles calculations of the formation energy of Cr/Al vacancies in spinel‐type MgCr2O4 and MgAl2O4
Authors: Moriwake Hiroki , Tanaka Isao , Oba Fumiyasu , Koyama Yukinori , Adachi Hirohiko 
Published: December 2002

AbstractQuantitative analysis of the formation energy of Cr vacancy in MgCr2O4 was made by first principles calculation. A 56‐atom supercell was employed and relaxation of atoms within the second‐nearest‐neighbor shell of the vacancy was taken into account. The formation energy was calculated as a function of the atomic chemical potential of Cr. Theoretical formation energy of Cr vacancy in MgCr2O4 shows negative values in the case of the oxidation limit of MgCr2O4, in good agreement with experimental results showing abundance of Cr vacancies when annealed in air. On the other hand, the formation energy of the Al vacancy in MgAl2O4 under the same condition is as large as 4.76 eV. This also corresponds well to the experimental fact that Al vacancy does not form alone in MgAl2O4 in air. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Optical excitations of Si by time‐dependent density functional theory based on exact‐exchange Kohn–Sham band structure
Authors: Kim Yong‐Hoon , Städele Martin , Görling Andreas 
Published: December 2002

AbstractWe calculate the imaginary part of the frequency‐dependent dielectric function of bulk silicon by applying time‐dependent density functional theory (TDDFT) based on the exact‐exchange (EXX) Kohn–Sham (KS) band structure and the adiabatic local‐density approximation (ALDA) kernel. The position of the E2 absorption peak calculated with the EXX band structure at the independent‐particle level is in excellent agreement with experiments, which demonstrate the good quality of EXX “KS quasiparticles.” The excitonic E1 peak that is missing at the independent‐particle level remains absent if two‐particle interaction effects are taken into account within the ALDA to TDDFT, demonstrating the incapability of the ALDA kernel to describe excitonic effects. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Density functional calculation of photoabsorption in metal clusters using an exchange‐correlation potential with correct asymptotic behavior
Authors: Torres M. B. , Balbás L. C. 
Published: December 2002

AbstractThe exchange‐correlation potential with the correct −1/r asymptotic behavior proposed by Parr and Ghosh (Phys Rev A 1995, 51, 3564) is used here to study the linear response to external fields of (1) neutral and charged sodium clusters, and (2) doped clusters of the type NanPb (n = 4, 6, 16). Our results for the photoabsorption cross section are compared with experiments, when available, and with previous density functional theory calculations using local and nonlocal functionals. The calculated static polarizabilities and plasmon frequencies are in better agreement with experiments than were previous calculations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Nonlocal WDA functional capable of describing the image potential of a metallic surface
Authors: García‐González P. , Alvarellos J. E. , Chacón E. , Tarazona P. 
Published: December 2002

AbstractIt is known that the exchange‐correlation (XC) potential vXC obtained using the nonlocal weighted density approximation (WDA) does not yield the image behavior −1/4z outside a metal surface. This limitation might be due to the fact that the WDA is based on an isotropic scaling of the electron pair correlation function. In this work we present a WDA scheme based on an anisotropic scaling for the pair correlation function showing that, in this case, the potential vXC has the correct imagelike decay. This new scheme does not entail a significant additional effort if compared with the standard WDA method. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Ferromagnetic instabilities in atomically thin lithium and sodium wires
Authors: Bergara A. , Neaton J. B. , Ashcroft N. W. 
Published: December 2002

AbstractUsing density functional theory, the ground‐state structural, electronic, and magnetic properties of monoatomic lithium and sodium chains with low average density are investigated. A metallic, zigzag ground‐state structure is predicted, but, most interestingly, stable equilibria for chains under tension are predicted to be ferromagnetic, which can be traced to exchange effects arising from occupation of the second subband as a function of the interatomic distance. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Two‐dimensional electron gas: Correlation energy versus density and spin polarization
Authors: Gori‐Giorgi Paola , Attaccalite Claudio , Moroni Saverio , Bachelet Giovanni B. 
Published: December 2002

AbstractWe propose a simple analytic representation of the correlation energy ϵc for the two‐dimensional electron gas, as a function of the density parameter rs and the spin polarization ζ. This new parametrization includes most of the known high‐ and low‐density limits and fits our new fixed‐node diffusion Monte Carlo simulations, performed for a wide range of electron densities (1 ≤ rs ≤ 40) and spin‐polarization states (0 ≤ ζ ≤ 1). In this way we provide a reliable local‐spin‐density energy functional for two‐dimensional systems. The corresponding correlation potential is discussed and compared with previous models. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Many‐fermion systems: Differential equations and kinetic energy functionals for different confining potentials
Authors: Howard I. A. , March N. H. 
Published: December 2002

AbstractDetermination of the kinetic energy functional is one of the central problems in the density functional theory of a many‐fermion system. We consider several many‐fermion systems to be characterized by simple confining potentials: the harmonic oscillator potential in one and three dimensions, the Coulomb potential, and the potential V(x) = −Uosech2(x/L). We discuss for each of these cases the differential equation that determines the fermion density in the given potential, and the corresponding kinetic energy density. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
First‐principles study of inter‐nitrogen interaction energy of Cu(100)‐ c(2 × 2)N surface
Authors: Yoshimoto Yoshihide , Tsuneyuki Shinji 
Published: December 2002

AbstractEffective interaction energy among nitrogen atoms on Cu(100)‐c(2 × 2)N surface was obtained by a density functional plane‐wave pseudopotential calculation. For efficient calculation of metallic systems, a preconditioning method for the local potential in self‐consistent field iteration was proposed. Attractive interaction energy among nitrogen atoms consistent with a high‐temperature STM experiment was obtained. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Ab initio calculations of magnetic properties of Fe–Cr trilayer as a function of ferromagnetic slab thickness
Authors: Pereiro M. , Baldomir D. , Man'kovsky S. , Arias J. 
Published: December 2002

AbstractMost of the articles devoted to giant magnetoresistance phenomenon take into account only the thickness variation of the spacer. Within this work, we study the magnetic behavior of the trilayer system Fe/Cr/Fe (0 0 1) after changing the thickness of the magnetic layers (Fe layers) and keeping the spacer constant (Cr layers). The calculations were done at the ab initio level by means of density functional theory, solving the Kohn–Sham equations with the full‐potential linearized augmented plane wave method. These results show an oscillatory behavior of magnetic moment per atom as a function of the iron monolayers number. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Excitation energies of molecules by time‐dependent density functional theory based on effective exact exchange Kohn–Sham potentials
Authors: Della Sala Fabio , Görling Andreas 
Published: December 2002

AbstractAn exchange‐only approach to calculate both valence and Rydberg excitation energies within time‐dependent density functional theory is presented. The ground‐state Kohn–Sham (KS) orbitals and eigenvalues are evaluated using an effective exact‐exchange KS potential, the localized Hartree–Fock potential. The exchange correlation kernel is taken into account within the adiabatic exchange‐only local density approximation. Results for the nitrogen molecule, ethylene, and benzene are presented. The calculated excitation energies exhibit the same accuracy as those obtained using various empirically parameterized asymptotically corrected exchange correlation KS potential although no empirical parameters are used and correlation is completely neglected. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Density functional theory from the extreme limits of correlation
Authors: Seidl Michael 
Published: December 2002

AbstractDensity functional perturbation theory for the correlation energy Ec[ρ] is equivalent to the Taylor expansion of the coupling‐constant integrand Wα[ρ] around its weak‐interaction limit α → 0. While this theory appears to diverge for many systems of interest (atoms, molecules, etc.), the opposite limit α → ∞ of strong interaction (which is mathematically simple) appears to provide just the missing information. Only the two leading terms of the perturbation expansion in the weak‐interaction limit are required for an accurate prediction of Ec[ρ] if they are extrapolated properly to the strong‐interaction limit. This interaction‐strength interpolation is demonstrated here for the helium atom, where the strong‐interaction limit can be treated rigorously. For general systems with more than two electrons, simple explicit approximations to that limit are available. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Exchange correlation energy as a function of the orbital occupancies: Implementation on first principles local orbital methods
Authors: Pou P. , Oszwałdowski R. , Vázquez H. , Pérez R. , Flores F. , Ortega J. 
Published: December 2002

AbstractWe introduce a local density formalism, where the total energy of the system is obtained as a function of the orbital occupancies {nμσ}. The exchange energy, EX is written in terms of the electrostatic interaction between a charge nμσ and its hole (1 − nμσ), while the correlation energy is analyzed by means of a Hubbard Hamiltonian using a dynamic field approximation. Once the exchange correlation energy is obtained as an explicit function of the {nμσ}, our orbital occupancy method is completely defined. Our approach is then applied to bulk diamond, Si, and zinc‐blende GaN, as well as the benzene molecule. The results obtained show that this approach offers an interesting alternative to the well‐established density functional theory methods based on the electron density ρ($\vec{r}$
). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003