bluuebunny/crossref_metadata_2025_split huggingface dataset:
Density functional theory for Jahn–Teller systems
Authors: Sukumar N. 
Published: January 2005

AbstractThe first discussion of the dynamics of Jahn–Teller systems in terms of the electronic density as the fundamental variable was given by W.J. Clinton in 1960, where the degenerate electronic configuration of a Jahn–Teller molecule was interpreted in terms of the infinite number of ways in which the charge distribution can be oriented for the same energy. The moving nuclear framework serves as the perturbation necessary to define the orientation of the charge density, with no activation energy required to put the charge cloud into motion. Recently, this notion of the electronic charge cloud in a Jahn–Teller molecule sweeping out the potential surface over which the nuclei move has found mathematical expression in our work in terms of a generalized electronic current density in nuclear‐coordinate space [N. Sukumar and B.M. Deb, Int. J. Quantum Chem. 40, 501 (1991)]. The introduction of the electronic phase as a function of both electronic and nuclear coordinates, in addition to the electronic density, is a crucial component of this formulation. In the present work, the density‐based treatment is extended to the nonadiabatic situation, with the Born couplings interpreted as nonadiabatic currents in parameter space. Abelian and non‐Abelian gauge transformations of these currents are discussed. © John Wiley & Sons, Inc.
Direct minimization of the energy in density functional theory
Authors: Fantucci Piercarlo , Polezzo Stefano 
Published: January 2005

AbstractThe minimization of the energy functional of the first‐order density matrix γ(r,r') is achieved using unitary transformations applied to γ. Equivalently, such transformations can be carried out also on one‐electron orbitals (natural orbitals) and their occupation (integer or non‐integer) numbers. The conventional local density approximation based on the electron density p(r) is then considered as a special case. The direct minimization of the energy functional of p with respect to the parameters of the unitary transformation leads to stationary conditions that are all equivalent to the Kohn–Sham equations. Preliminary numerical tests show that the proposed algorithms for the direct minimization of the energy work in a satisfactory manner. © John Wiley & Sons, Inc.
The dependence of 10Dq upon the metal–ligand distance, R, for transition‐metal complexes. What is its microscopic origin?
Authors: Moreno M. , Barriuso M. T. , Aramburu J. A. 
Published: January 2005

AbstractExperimental results on 3d Oh complexes in insulators reveal that 10Dq α R−n, where R is the metal–ligand distance and n is close to five. This strong dependence determines the Huang–Rhys factor, S(A1g), associated to the symmetric A1g mode of the first excited state of complexes like MnX and CrX (X = halide) and makes it possible to measure R changes down to ∽ 10−3 Å. This work is devoted to understanding, within a molecular orbital framework, the microscopic origin of such a dependence, which is related to the corresponding one displayed by the transferred spin densities fσ, fs, and fπ. The analysis is focused on MnF. As a main result, it is shown that though fσ ≫ fs the interaction between d(eg) orbitals and 2s orbitals of F− is not only primarily responsible for the R dependence of 10Dq but also makes a significant contribution to the 10Dq value itself. The present work thus shows that the significant dependence of 10Dq upon R is ultimately related to the strong dependence of fs and the isotropic superhyperfine constant As upon R displayed by the experimental results of several 3d impurities. © John Wiley & Sons, Inc.
Predictive chemical kinetics: Density functional and hartree–fock calculations on free‐radial reaction transition states
Authors: Green William H. 
Published: January 2005

AbstractDensity functional theory (DFT) using gradient‐corrected «nonlocal» functionals is used to calculated the thermochemistry and barrier heights for several types of peroxyl radical isomerizations currently being studied by kineticists. The calculations are generally in good agreement with experimental data, where such data are available. An important exception is that the O—H bond strengths in hydroperoxides are all predicted to be too weak by about 7 kcal/mol. The calculated reaction barriers are a few kcal/mol lower than the experimental estimates, but comparable in accuracy to the much more computationally expensive second‐order Møller–Plesset (MP2) predictions. Various theoretical methods converge on a 42 ± 2 kcal/mole barrier for CH3OO → H2CO + OH. The DFT calculations can be used to predict reaction barriers in cases where no reliable experimental data are available. The effects of the choice of basis set and correlation functional are explored. Improvements needed to make these calculations most valuable to the chemical kineticist are discussed. © 1994 John Wiley & Sons, Inc.
Density functional theory applied to the excited states of coordination compounds
Authors: Daul Claude 
Published: January 2005

AbstractCoordination compounds are usually symmetrical molecules with degenerate orbitals. Hence, the individual multiplet states arising from open‐shell configurations can, in general, not be expressed by a single determinant. We have therefore exploited symmetry to the largest possible extent in order to simplify the relation between the multiplet splitting and single‐determinant energies and thus developed a new method based on vector coupling to keep the computational effort to a minimum. A system of computer programs working on both mainframe and personal computers has been developed, carrying out for any desired point group the required group theoretical manipulations. The description of the method is illustrated by considering three practical examples. © 1994 John Wiley & Sons, Inc.
The effects of nonlocal gradient corrections in density functional calculations of hydrocarbon radical hyperfine structures
Authors: Eriksson Leif A. , Malkin Vladimir G. , Malkina Olga L. , Salahub Dennis R. 
Published: January 2005

AbstractGround‐state equilibrium geometries and hyperfine structures of a number of organic neutral and charged radical compounds are computed using the linear combination of Gaussian‐type orbitals–density functional theory method. In addition to the local spin‐density approximation, we also use two different nonlocal (gradient corrected) schemes for the calculations of the exchange and correlation potentials. The different functional forms are found to generate slightly different total and unpaired spin‐density distributions in the molecules, and as a result, the computed isotropic hyperfine coupling constants vary markedly. The smallest variations are found for the hydrogens, where the results are generally in satisfactory agreement with experiment. For the carbon atoms, however, large differences in isotropic coupling constants are observed. The anisotropic hyperfine structures are generally very well described at all levels of theory. © John Wiley & Sons, Inc.
Electronic structure of paramagnetic clusters of transition metal ions. 3. Magnetic properties and scattered wave description of the electronic structure of the hexanuclear octahedral cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2
Authors: Bencini Alessandro , Uytterhoeven Myriam G. , Zanchini Claudia 
Published: January 2005

AbstractSpin‐polarized Xα–SW calculations of [Fe6(μ3−S)8(PH3)6]2+ as a model of the cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2 have been performed. The highest occupied energy levels are well separated from empty levels, and up to a maximum of eight electrons can be unpaired, giving a maximum spin state with S = 4. This electronic state is consistent with the magnetic data of [Fe6(μ3−S)8(PEt3)6](BPh 4)2, which have been interpreted using the Heisenberg–Dirac–Van Vleck exchange spin Hamiltonian. The S = 4 state arises from the magnetic coupling between five low‐spin (Si = 1/2) and one intermediate‐spin (S = 3/2) iron(III) center. © 1994 John Wiley & Sons, Inc.
Geometrical and spectroscopical characterizations of some complex entities of aluminum(III) with fluoride ions by LDF‐based calculations
Authors: Bouyer Frédéric , Picard Gérard , Legendre Jean‐jacques 
Published: January 2005

AbstractThe structure of cryolite is investigated with a theoretical approach based on LDF calculations. In fact, experimental techniques for structural studies are difficult to perform in cryolite melts because of hard experimental conditions (high temperature, corrosiveness, etc.). Use of the DMol software allows us to determine the stabilities and the vibrational frequencies of AlF, AlF, and AlF isolated complexes. The results obtained compared with published experimental works confirm that AlF should be considered in the dissociation scheme of cryolite as previously evidenced by other authors. © 1994 John Wiley & Sons, Inc.
Symmetry breaking and its influence on the correlation energy for CF and CF ions
Authors: Garcia de la vega J. M. , San fabian E. 
Published: January 2005

AbstractWe have studied symmetry breaking in three open‐shell systems: CF (D2d and C2v) and CF (D3h) molecular ions. These different Hartree–Fock solutions are employed as starting points to calculate the correlation energy of these ions with perturbative, configuration interaction, and density functional methods. When symmetry‐broken or symmetry‐adapted wave functions are used, the correlation energy obtained with each method changes the order of stability of CF for a determined symmetry. Density functional methods produce higher correlation energies although they do not alter the order of stability of Hartree–Fock calculations. The behavior of correlation energy with different methods and the characteristics of the symmetry of wave functions are compared. A study of appearance energies for three different channels of the decomposition reaction of ionized carbon tetrafluoride are considered by using different methods with symmetry‐broken or symmetry‐adapted wave functions to calculate correlation energies. © 1994 John Wiley & Sons, Inc.
Investigations of hydrogen‐bonded systems: Local density approximation and gradient corrections
Authors: Kaschner R. , Seifert G. 
Published: January 2005

AbstractThe applicability of the local density approximation (LDA) and of corresponding gradient corrections (for the exchange and correlation energy) for the treatment of the hydrogen bond is investigated. As test systems, we consider the water dimer and the H2O…︁HX complexes (X = F, Cl, Br): Using an LCAO scheme, their equilibrium geometries and interaction energies are ćalculated and compared with experimental data and with other calculations. We obtain that the LDA gives the geometries in qualitative agreement with other data, whereas the energies are overestimated. The use of the gradient corrections (GC) according to Becke and Perdew leads to a significant improvement of the geometry, and especially of the interaction energies. The calculations indicate further that LDA + GC should also be able to describe weaker intermolecular interactions than the usual hydrogen bond. Finally, a short discussion of the charge distribution and the dipole moments of the H2O…︁HX complexes is performed. © 1994 John Wiley & Sons, Inc.
Density functional theory: An effective theoretical tool for the study of σ radicals
Authors: Barone Vincenzo , Adamo Carlo , Russo Nino 
Published: January 2005

AbstractThe structures, harmonic force fields, and hyperfine coupling constants of a number of representative σ radicals have been investigated by the density functional approach including nonlocal corrections. Scaling of CH bond lengths and stretching constants leads to accurate structures and force fields. Hyperfine coupling constants reach, at least, the level of the most sophisticated conventional post‐Hartree–Fock models. This suggests that the density functional approach is a promising theoretical tool for the study of relationships between structure and spectroscopic properties of large free radicals. © 1994 John Wiley & Sons, Inc.
Bonding of acetylene to copper atom, dimer, and trimer
Authors: Fournier René 
Published: January 2005

AbstractThe bonding of acetylene to copper atom, dimer, and trimer was investigated with a Kohn–Sham density functional approach. Full geometry optimization yielded the equilibrium structures of various CunC2H2 species. Gradient corrections were included in the calculation of binding energies (BE). The Cu—C2H2 complex was found to have a Cs structure and a BE of 10 kcal/mol. Three isomers of Cu2C2H2 have similar total energies: a C2v end‐bonded structure with a BE of 18 kcal/mol, and two 1,2‐dicupro ethylene isomers—a cis form with a BE of 12 kcal/mol and a trans form with a BE of 15 kcal/mol. Two stable C2v isomers of Cu3C2H2 were found. In both isomers, the Cu3 ring relaxes from its isosceles structure, with two short bonds (2.247 Å) and one long bond (2.478 Å), and adopts a nearly equilateral geometry. In one isomer of Cu3C2H2, the acetylene is bonded to one apex of the Cu3 ring with a BE of 29 kcal/mol. In the other, it is bonded to two copper atoms of one side of the Cu3 ring with a BE of 33 kcal/mol. © 1994 John Wiley & Sons, Inc.
Self‐consistent calculations of total energies and charge densities of solids without solving the band‐structure problem
Authors: Cortona Pietro , Monteleone Andrea Villafiorita 
Published: January 2005

AbstractWe have used a recently proposed method allowing a direct calculation of the total energy and of the charge density of a crystal to determine the equilibrium lattice parameter, the cohesive energy, and the bulk modulus of MgO and CaO. The results that we have obtained are compared with those of a variety of band‐structure calculations as well as with the experimental data. © 1994 John Wiley & Sons, Inc.
On the electronic structure of MoO: Spin‐polarized density functional calculations of spectroscopic properties of low‐lying quintet, triplet, and septet states
Authors: Brocławik Ewa , Salahub Dennis R. 
Published: January 2005

AbstractDensity functional theory (DFT) calculations for the ground state and four excited quintet, two septet, and two triplet states of the molybdenum oxide molecule are reported. Equilibrium geometries and other spectroscopic constants are determined for these states and compared both with recent spectroscopic measurements and other theoretical calculations, where available. Experimental assignments of the 5II ground state and excited 5Σ+, 5Σ−, 5Δ, and B' 5II states are confirmed; also candidates for low‐lying triplet3 Δ and 3Σ− and septet 7II and 7Σ+ are presented. Theoretical calculations for 5Σ−, B' 5II, and 3Σ− states are reported for the first time. The results are in many cases in better agreement with experiment than are other calculations, already at the simplest level of approximation within DFT, which confirms that this method is a useful tool for investigation of transition‐metal compounds. © 1994 John Wiley & Sons, Inc.
Applicability to atoms of a large set of correlation energy functinals
Authors: San fabián E. , Moscardó F. , Pérez‐jordá J. M. 
Published: January 2005

AbstractAn extensive study of the application of a large set of correlation energy functionals to atomic systems is presented. Hartree–Fock densities and, sometimes, generalized‐valence‐bond wave functions are used. The functionals have been grouped into four sets: (I) local density and local spin density, (II) local spin density with self‐interactioon correction, (III) local spin density with gradient correction, and (IV) methods found on the correlation factor approach. In this bench mark, we report the results of calculations made for the ground states of the first and second rows, their anions and cations, and the two‐ and four‐isoelectronic series. © 1994 John Wiley & Sons, Inc.
A density functional study of pseudotetrahedral metal–nitrosyl complexes
Authors: Bohr F. , Chermette H. , Ruiz‐lópez M. F. 
Published: January 2005

AbstractLocal and nonlocal density functional computations have been carried out to study the electronic structure and the equilibrium geometry of the isoelectronic series Cr(NC)4, Mn(NO)3(CO), Fe(NO)2(CO)2, and Co(NO)(CO)3 and model compounds Fe(NO)2L2 (L = Cl, HCN, NH3, PH3, and C2H4). The structure of Fe(NO)2(C4H6) is also described. The discussion is focused on structural modifications through a change of ligand, in particular those concerning the metal‐nitrosyl conformation (linear vs. bent). Though this is a preliminary study of metal–nitrosyl properties by DFT methods and more computations are required to analyze the mechanism of homogeneous catalysis processes, our results support the hypothesis that structural reorganization from linear to bent metal–nitrosyl plays a key role in some reactions, such as in butadiene dimerization. © 1994 John Wiley & Sons, Inc.
An insight into optical and EPR properties of AgCl and AgF complexes through MS–Xα and SCCEH calculations
Authors: Valiente R. , Aramburu J. A. , Barriuso M. T. , Moreno M. 
Published: January 2005

AbstractMS‐Xα and SCCEH calculations on the Ag2+ complexes AgF and AgCl (displaying an elongated D4h symmetry) have been carried out for a better understanding of their experimental optical and EPR properties. As salient features, the present work supports that the unpaired electron in AgCl spends a little more time on ligands than on Ag2+, in agreement with the previous analysis of EPR and optical data for KCl:Ag2+. Furthermore, the five experimental optical transitions observed in that case are reasonably assigned. The first transition (observed at 12,500 cm−1) is assigned to a jump involving the 5a1g orbital built mainly (∽70%) from 3p orbitals of axial ligands, a fact that reflects the distinct level scheme for AgCl when compared to that for more ionic complexes. Calculations on AgF and AgF performed as a function of the equatorial Ag2+ –F− distance led to a reasonable understanding of experimental gyromagnetic and superhyperfine tensors displayed by Ag2+ in fluorides. The different relative decrease undergone by g‖– go (8%) and g ⟂ – go (28%) on passing from CsCdF3:Ag2+ to RbCdF3:Ag2+ is shown to be consistent with the formation of AgF and AgF complexes, respectively, related to the different substitutional position of Ag2+ in such lattices. The decrement of about 8.5% experienced by both g‖ – go and g⟂ – go values on going from CsCdF3:Ag2+ to NaF:Ag2+ is pointed out to reflect the different electrostatic potential (exerted by the rest of the lattice upon the complex) seen by AgF embedded in NaCl or perovskite‐type lattices. © 1994 John Wiley & Sons, Inc.
The chemisorption of hydrogen on Cu(111): A dynamical study
Authors: Forni A. , Wiesenekker G. , Baerends E. J. , Tantardini G. F. 
Published: January 2005

AbstractAb initio band‐structure calculations within a density functional formalism were performed to compute the binding energy curves of atomic hydrogen with the high‐symmetry adsorption sites of the (111) surface of copper. For a two‐layer slab of Cu atoms and H coverage equal to 0.25, the binding energies are 2.25, 3.12, and 3.24 eV, for on‐top, bridge, and threefold sites, so that the chemisorption of H2 on Cu(111) is exothermic for threefold and bridge sites, but endothermic for on‐top sites. Starting from these results, an LEPS potential for the interaction of H2 with the Cu(111) surface was built. In this model potential, the most favored approaches correspond to a H2 molecule parallel to the Cu surface, and for them, the activation barrier is located at the corner between the entrance and the exit channels of the reaction, and its lowest value is 0.6 eV. The LEPS potential was used in quasi‐classical trajectories calculations to simulate the adsorption of a beam of H2 molecules on Cu(111). The results show that (a) when H2 is in the ground vibrational state the dissociative adsorption probability Pa increases from 0 to .90 along a roughly sigmoidal curve by increasing the collision kinetic energy from 0.4 to 1.3 eV, and (b) the vibrational energy can be as effective as the translational one in promoting dissociative chemisorption, in agreement with the experimental results. © 1994 John Wiley & Sons, Inc.
SystematicLSDinvestigation on cationic boron clusters: B(n 2–14)
Authors: Boustani Ihsan 
Published: January 2005

AbstractThe geometrical structures and properties of small cationic boron clusters B(n= 2–14) have been investigated using the local spin density (LSD) formalism. The nonlocal correction has also been calculated. The linear search for minima on the potential energy surface has been performed using analytical gradients of theLSDtotal energy. Most of the final structures of the cationic boron clusters prefer planar or quasi‐planar nuclear arrangements and can be considered as fragments of a planar surface or as segments of a sphere. The calculated adiabatic ionization potentials of Bnexhibit features that are analogous to those of measured ionization potentials for boron clusters. Most of the calculated normal modes of the cationic clusters have frequencies that are around 1000 cm−1and have strong infrared intensities, and they correspond quite well with analogous properties of solid boron. © 1994 John Wiley & Sons, Inc.
First principles calculation of the optical properties and stability of hydrogenated silicon clusters
Authors: Hirao Masahiko , Uda Tsuyoshi 
Published: January 2005

AbstractOptical properties and stability of hydrogenated silicon clusters are investigated using density functional pseudopotential calculation. The dipole transitions between the band‐edge orbitals are allowed, in contrast to the indirect gap in bulk silicon. Evolution of a small amount of hydrogen atoms enhances the dipole transition, increasing the photoluminescence intensity. Further dehydrogenation creates gap states due to dangling bonds, which may decrease the photoluminescence intensity via nonradiative recombination processes. The Stokes shift is also estimated by calculating the relaxed structure of the excited state within the local density approximation. © 1994 John Wiley & Sons, Inc.
Natural polyelectron population analysis
Authors: Parrondo Ramóan M. , Karafiloglou Padeleimon , Marcos Enrique Sánchez 
Published: January 2005

AbstractA method to perform a polyelectron population analysis of correlated molecular orbital wave functions on the basis of natural atomic orbitals (NAOs), as given by Weinhold, is presented. The method allows calculations of the probabilities of finding various types of electronic events occuring in some target AO positions, including the contributions of ionic and covalent resonance structures. This method is general and neither the theory nor the developed algorithm limit the number of electrons and holes that can be considered. Thus, the analyzed MO wave function can be a usual CI or a MCSCF one, and apart from Weinhold's NAOs. any other type of orthogonal AOs can be used as analyzers, provided that these AOs are linear combinations of the SCF‐AOs. Numerical applications are given for ethylene, formaldehyde, butadiene, and acroleine, by adopting various AO basis‐set levels (STO−4G, 4–31G, and 6–31G) and by analyzing correlated wave functions (CISD). Improvements in the polyelectron populations when increasing the quality of AO basis sets and the corresponding valence NAOs are revealed by several examples. Furthermore, it is shown that the electroegativity of oxygen in acroleine only has an effect on contributions of ionic and covalent resonance structures, but not on delocalization of the double bonds. 1993 John Wiley & Sons, Inc.
Evaluation of cross sections for X‐ray and high‐energy electron scattering from molecular systems
Authors: Wang Jiahu , Smith Vedene H. 
Published: January 2005

AbstractAn analytical and computationally efficient formalism for the evaluation of rotationally averaged cross sections for X‐ray and high‐energy electron scattering from molecular systems is given. Its application for both SCF and CI wave functions is discussed. © 1994 John Wiley & Sons, Inc.