bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the use of corresponding orbitals for the construction of mutually orthogonal orbital sets
Authors: Broer R. 
Published: January 2005

AbstractConsider two orbital sets χk, k = 1…m and η1, 1 = 1…n, which are mutually nonorthogonal. Provided that n > m, at least n − m orbitals of the set {η} can be orthogonalized to the set {χ} by a transformation within the set {η}. The orthogonalization of the remaining orbitals of {η} to the set {χ} requires a transformation in which the χk appear explicitly. The orthogonalization of one orbital set to another is relevant for SCF optimizations in a truncated basis set, in the presence of frozen occupied orbitals. Examples are frozen core calculations, ECP calculations, and embedded cluster calculations, where the cluster is embedded in a frozen environment. A simple orthogonalization scheme, which makes use of a corresponding orbital transformation, is presented. It is suggested that with a small, well‐defined extension of the set {η} the complete orthogonalization can be done with a transformation in which the {χ} do not appear explicitly. © 1993 John Wiley & Sons, Inc.
Multiconfigurational second‐order perturbation theory: A test of geometries and binding energies
Authors: Andersson Kerstin , Roos Björn O. 
Published: January 2005

AbstractMulticonfigurational second‐order perturbation theory is tested for the calculation of molecular structure and binding energies. The scheme is based on the Complete Active Space (CAS) SCF method, which gives a proper description of the major features in the electronic structure, independent of its complexity, accounts for all near degeneracy effects, and includes full orbital relaxation. Remaining dynamic electron correlation effects are in a subsequent step added using second‐order perturbation theory with the CASSCF wave function as the reference state (CASPT2). The approach is applied to the calculation of equilibrium geometry and atomization energies for 27 benchmark molecules containing first‐row atoms (the “G1” test). Large atomic natural orbital (ANO)‐type basis sets are applied (5s4p3d2f for LiF and 3s2p1d for H). It is shown that the CASSCF/CASPT2 approach is able to predict the equilibrium geometry with an accuracy better than 0.01 Å for bond distances and 0°–2° for bond angles. Calculated atomization energies are underestimated with between 3 and 6 kcal/mol times the number of extra electron pairs formed. The error in the heat of reaction for a number of isogyric reaction (no difference in number of pairs) varies between −2.5 and +1.0 kcal/mol. The same type of accuracy is obtained in calculations for excited states. The molecules B2, C2, FO, FOO, and FOOF have also been studied. Results for the first three molecules are in accordance with those of the benchmark molecules. The FO bond distance in FOO is predicted to be 0.02 Å longer than experiment. The heat of formation for FOO is computed to be 2.9 kcal/mol with an uncertainty of ±3 kcal/mol. Preliminary results for FOOF (obtained with a smaller basis set) indicate that the approach yields a somewhat too long FO bond distance (1.64 Å compared to 1.58 Å experimentally). © 1993 John Wiley & Sons, Inc.
Resolution of Schrödinger's equation for a scattering problem by a finite‐element method
Authors: Laloyaux Th. , Vigneron J.‐P. , Lambin Ph. , Derycke I. , Lucas A. A. 
Published: January 2005

AbstractWe present a new numerical method for solving the Schrödinger equation in the case of scattering or tunneling states. As an example, we study a model of the scanning tunneling microscope. The method uses a finite‐element approximation of the wave function in the region of the scattering potential. From the wave function that we obtain, we derive the tunnel current density. © 1993 John Wiley & Sons, Inc.
The effects of atomic multipole moments obtained by the potential‐derived method on hydrogen bonding
Authors: Kong Jing , Yan Ji‐Min 
Published: January 2005

AbstractA potential‐derived atomic multipole method called the cumulative potential‐derived atomic multipole method is developed, with which electrostatic atomic multipole moments are derived by fitting the molecular electric potential in a cumulative way. It is applied to the hydrides of N, O, F, S, Cl, and methanol and the hydrogen‐bonded dimers formed between them. The relationship between atomic multipole moments and molecular charge distributions is found. The structures calculated with Buckingham's electrostatic model are in good agreement with experiments. The phenomena of nonlinear structures of most H‐bonded complexes—the deviations of symmetry axes of electron donors from H bonds—and correct distinguishing between two alternative structures are attributed to atomic dipole and quadrupole moments. Compared with other methods, this method has a quantitative and qualitative advantage and simple algorithm. The main conclusion is that the atomic multipole moments play a substantial role, although a potential‐derived charge model was deemed sufficient previously. © 1993 John Wiley & Sons, Inc.
Dissipative and coherent dynamics induced by a nonadiabatic electron–phonon coupling: Aspects of superconductivity
Authors: Baňacký Pavol , Svrček Michal 
Published: January 2005

AbstractBand structure with a quasicontinuum of electronic states near the Fermi surface (FS) of a solid‐state matter indicates overlapping regions of the electronic and phonon spectra: (εP – εQ) ≈ ℏωv. This simple fact has an important impact on the theoretical aspects of the description and a study of an electronic structure and physical properties of a matter since velocities of the nuclei and electrons are on the same scale. The motion of the electrons is not adiabatic and the description of the electronic structure of a system cannot be based on the assumption of the validity of Born‐Oppenheimer approximation. For nonadiabatic systems in contrast to the descripton of adiabatic systems [(εp – εQ) > ℏωv], an effect of the finite mass of the electrons, i.e.˙ nonadiabatic corrections, cannot be calculated by a perturbation theory due to the divergency of a perturbation expansion. Quasiparticle transformation technique has disclosed the unexpected effects of nonadiabaticity on the electronic structure and physical properties of matter. The aspects of superconductivity are discussed. © 1993 John Wiley & Sons, Inc.
The optimized‐basis‐set multiconfiguration spin‐coupled method for the ab initio calculation of atomic and molecular electronic wave functions
Authors: Penotti Fabio E. 
Published: January 2005

AbstractAn ab initio method for the calculation of atomic and molecular electronic wave functions is presented. The “Optimized‐Basis‐Set Multiconfiguration Spin‐Coupled” (OBS–MCSC) method may be viewed either as a multiconfiguration generalization of the spin‐coupled approach or as a nonorthogonal variant of the MCSCF method. In addition, the OBS–MCSC method optimizes the basis‐set exponential parameters simultaneously with all other variational parameters, through a second‐derivative minimization procedure. Explicit analytic expressions for the required first and second derivatives of the energy with respect to all variational parameters are obtained. Test calculations prove the capability of the method to yield compact yet accurate electronic wave functions.© 1993 John Wiley & Sons, Inc.
Electron structure of a high‐spin hydrocarbon polyallyl: Hubbard approximation with a strong electron repulsion
Authors: Cheranovskii V. O. 
Published: January 2005

AbstractThe Hubbard model of the polyallyl chain with a strong repulsive potential and one hole in the half‐filled band is reduced to the effective spin Hamiltonian. In the case of infinite repulsion, the exact spectrum of the model with cyclic boundary conditions is obtained.© 1993 John Wiley & Sons, Inc.
Reaction path as a gradient line on a potential energy surface
Authors: Minyaev Ruslan M. 
Published: January 2005

AbstractThe reaction path is shown to be always a gradient line on a potential energy surface (PES) of a molecule. The properties of gradient lines on the PES are elucidated. Correct symmetry conservation rules along the gradient line are derived. The behavior of the gradient line on a PES with different topologies are considered. © 1994 John Wiley & Sons, Inc.
Maximum hardness in P6 isomers
Authors: Warren D. Scott , Gimarc Benjamin M. 
Published: January 2005

AbstractParr and Chattaraj proposed a principle of maximum hardness for stable molecular structures. Pearson and Palke used ab initio SCF MO calculations for ammonia and ethane to demonstrate the operation of the principle. In this paper, we present ab initio SCF MO results for five isomeric forms of the homoatomic P6 cluster as further support for the principle of maximum hardness. © 1994 John Wiley & Sons, Inc.
Study on improving the accuracy of the total energy calculated by the DV–Xα method
Authors: Li Le‐Min , Hong Gong‐Yi 
Published: January 2005

AbstractThe effect of the truncation errors resulting from the numerical integration on the accuracy of the calculation results in the DV–Xα method is analyzed and it is shown that evaluating the overlap integrals analytically or adopting orthogonalized basis sets can reduce the errors on the density matrices to the second order. An approach to improve the calculation accuracy of the total energy is proposed based on the error analysis. The calculation results for several molecules are presented to demonstrate the conclusion. © 1994 John Wiley & Sons, Inc.
Applications of molecular dynamics simulations coupled with Harris functional approximation to argon
Authors: Lee Chengteh , Long Xiping , Carpenter Ilene , Smithline Shep , Fitzgerald George 
Published: January 2005

AbstractWe have demonstrated molecular dynamics simulations using a combination of the classical molecular dynamics with density functional theory for argon clusters. Three different molecular dynamics schemes, which differ in their treatment of the potential energy and forces, have been carried out. The first uses a Lennard‐Jones potential. In the second, the potential is computed using the Harris functional, and in the third, a combination of Lennard‐Jones and Harris functional potentials is used. In addition to direct examination of the trajectories, the velocity autocorrelation function and its power spectrum have been computed to demonstrate the agreement between these three methods. The present studies show that a scheme that used a combination of model potentials and density functional theory provides a very useful tool for the dynamics simulation of systems that contain some fragments in which the analytical model potentials are not available. © 1994 John Wiley & Sons, Inc.
A correlation‐energy functional from a correlation‐factor model
Authors: Fuentealba P. 
Published: January 2005

AbstractIn this work, a way to approximate the correlation energy functional starting from a model correlation factor is shown. The problem is addressed by using formally exact properties of the second‐order density matrix and actual values of correlation energies for atoms. An Ansatz for the correlation factor is proposed that allows one to derive some known and some new correlation energy density functionals. Results for atomic systems show the reliability of the approach. © 1994 John Wiley & Sons, Inc.
Large‐Z and ‐N dependence of atomic energies from renormalization of the large‐dimension limit
Authors: Kais Sabre , Sung Stella M. , Herschbach Dudley R. 
Published: January 2005

AbstractBy combining Hartree–Fock results for nonrelativistic ground‐state energies of N‐electron atoms with analytic expressions for the large‐dimension limit, we have obtained a simple renormalization procedure. For neutral atoms, this yields energies typically threefold more accurate than the Hartree–Fock approximation. Here, we examine the dependence on Z and N of the renormalized energies E(N, Z) for atoms and cations over the range Z, N = 2 → 290. We find that this gives for large Z = N an expansion of the same form as the Thomas–Fermi statistical model, E → Z7/2(C0 + C1Z−1/3 + C2Z−2/3 + C3Z−3/3 + ⃛), with similar values of the coefficients for the three leading terms. Use of the renormalized large‐D limit enables us to derive three further terms. This provides an analogous expansion for the correlation energy of the form δE δZ4/3(δC3 + δC5Z−2/3 + δC6Z−3/3 + ⃛); comparison with accurate values of δE available for the range Z ⩽ 36 indicates the mean error is only about 10%. Oscillatory terms in E and δE are also evaluated. © 1994 John Wiley & Sons, Inc.
Electronegativity dynamics in a chemical reaction
Authors: Chattaraj P. K. , Nath S. 
Published: January 2005

AbstractA generalized nonlinear Schrödinger equation has been solved in order to understand how electronegativity and the covalent radius of an atom vary during a chemical reaction. The chemical reaction is modeled as an atom in an external field and also as an atom colliding with an ion. Temporal evolution of charge density, current density, and effective potential has also been studied for a better understanding of the process. © 1994 John Wiley & Sons, Inc.
Analytic properties of connected moments expansions
Authors: Mancini Jay D. , Zhou Yu , Meier Peter F. 
Published: January 2005

AbstractThe derivation of the connected moments expansion (CMX) is examined as well as the singularities that arise in the series expansion for the ground‐state energy. Explicit analytic results are presented that show a canceling of these singularities. Also, an alternate moments expansion (AMX) is derived that closely models the CMX but displays a varied computational range. © 1994 John Wiley & Sons, Inc.
Calculation of electric dipole transition moments using quasi‐degenerate variational perturbation theory and averaged coupled‐pair functional theory
Authors: Cave Robert J. , Johnson Jenifer L. , Anderson Mark A. 
Published: January 2005

AbstractResults are reported from calculations of electric dipole transition moments for various electronic transitions in Be, CH2, and A1H using multireference singles and doubles configuration interaction, quasi‐degenerate variational perturbation theory, and multireference averaged coupled pair functional theory. A simple normalization scheme is used for the quasi‐degenerate variational perturbation theory and multireference averaged coupled pair functional theory wave functions. In all cases, comparison is made with full configuration interaction results in the valence space. For Be and CH2, all methods are of comparable quality in calculating the transition moments and excitation energies, with averaged coupled‐pair functional theory yielding slightly quicker convergence of the excitation energies and transition moments in most cases. For AlH, multireference singles and doubles configuration interaction is somewhat more accurate for the calculation of the transition moment. Factors that affect the accuracy of the methods are discussed. © 1994 John Wiley & Sons, Inc.
Aromaticity in metallacyclobutadienes from the perspective of the valence bond theory
Authors: Rincón Luis 
Published: January 2005

AbstractThe valence bond method has been implemented for the study of π‐electron systems using a semiempirical CNDO‐type Hamiltonian. The algorithm used is based on the Clifford algebra realization of the Rumer–Weyl basis presented by Paldus et al. Using this version of the CNDO–VB approach, the effect of the metal hybridization in the electronic delocalization of metallacyclobutadienes is discussed. © 1994 John Wiley & Sons, Inc.
On conjugated–circuit polynomials
Authors: Klein Douglas J. , Randić Milan , Babić Darko , Trinajstić Nenad 
Published: January 2005

AbstractRecursive formulas are derived for generating the conjugated‐circuit polynomials for circuits up to size n = 6, 10, or 14 on regular chain polyhex graphs. These counting polynomials are of use for a simple valence‐bond resonance‐theoretic derived model: the conjugated‐circuit model. © 1994 John Wiley & Sons, Inc.
Accurate upper and lower bounds to the 2S states of the lithium atom
Authors: Lüchow A. , Kleindienst H. 
Published: January 2005

AbstractThe first nonrelativistic lower bound to the ground state of the lithium atom is give with E0 > −7.47816 au using the method of variance minimization and an extension of Temple's formula. With large Hylleraas–CI basis sets, high‐precision upper bounds and isotope shifts are calculated for the three lowest 2S states of the lithium atom, which are best to date. © 1994 John Wiley & Sons, Inc.
The structure of water in human ras oncogene proteins
Authors: Yu Jeong Yun , Shin Jae Kwang , Jhon Mu Shik 
Published: January 2005

AbstractHigh‐directional Monte Carlo (HDMC) simulations are performed to investigate the behavior of water molecules in the catalytic sites of human ras p21 proteins and the results are compared among three types of hydrated ras p21 proteins: the normal ras complexed with GDP (normal‐p21/GDP), the mutant ras complexed with GDP (mutant‐p21/GDP), and the normal ras complexed with GTP (normal‐p21/GTP). Also, the original Metropolis Monte Carlo (MMC) simulation is performed on the normal‐p21/GDP system. Comparison between HDMC and MMC shows the improved efficeincy of HDMC on this complicated system. Interaction between water molecules is represented by the TIP3P potential function. The solute–water interaction is represented by the Coulomb and van der Waals interactions from the CHARMM force field spliced with TIP3P. The mean‐square displacements and dipole correlation functions are reported. We specifically examined the hydrogen‐bond interactions existing near the catalytic sites, by the distribution of small water clusters connected by the hydrogen bond and by the average lengths and fluctations of hydrogen bonds between water molecules and solute atoms. Water molecules form different local structures in different types of the p21/GDP(GTP) complexes. The structure and motion of water molecules near the catalytic sites of the proteins are discussed in detail. © 1994 John Wiley & Sons, Inc.
Semisimilarity of molecular bodies: Scaling–nesting similarity measures
Authors: Mezey Paul G. 
Published: January 2005

AbstractA simple, new technique for the evaluation of the similarity of molecular shapes is presented. The concept of semisimilarity (asymmetric similarity) is applied within the topological–geometrical framework of scaling–nesting similarity measures of molecules. The practical application of these similarity measures is illustrated by the examples of the three‐dimensional formal bodies of electronic charge densities of a set of simple molecules. © 1994 John Wiley & Sons, Inc.
Electron crystallization in two dimensions
Authors: Iyakutti K. , Palanichamy R. Rajeswara 
Published: January 2005

AbstractThe ground state of the 2D electron crystal is investigated using a localized representation for the electrons. Assuming a neutralizing background, calculation for a nonmagnetic electron crystal is performed. The areal electron densities corresponding to the crystallization for different rs values are computed and these are compared with the available experimental areal densities. An upper limit for the obtainable areal density has been predicted from our results. © 1994 John Wiley & Sons, Inc.
Alternating charge densities, peierls distortion, and charge‐conjugation symmetry in correlated one‐dimensional diatomic systems
Authors: Kuprievich Victor A. 
Published: January 2005

AbstractThe full‐optimized‐APSG approach based on the MC SCF technique is developed and applied to study ground‐state properties of one‐dimensional correlated systems. The effects of electron–electron interactions and bond relaxation are considered for the conjugated diatomic polymer; charge distribution and bond relaxation are calculated for the N = 50 chain within a wide range of site energy and e–e integral modulation involving the case of alternancy symmetry for diatomic systems. With relation to the results obtained, the problem of the neutral–ionic transition in mixed‐stack crystals is discussed. © 1994 John Wiley & Sons, Inc.
On the stability of the autodissociative ground electronic state of BeH2+
Authors: Chrysos Michael , Alikhani M. Esmail , Jacon Marcel 
Published: January 2005

AbstractIt is shown that the mechanism of spontaneous infrared emission enhances substantially the stability of the long‐lived ground electronic state of the exotic BeH2+, whose autodissociation becomes possible only via tunneling. The system, initially situated in any vibrational level (except the high‐lying ones for which dissociation is predominate) and statistically distributed over all rotational states, reaches stability through a cascade of dipole emissions toward lower levels. The rapid spatial variation of the dipole moment results in fast radiative processes and might suggest experimental observations easier to perform. The methodology is based on a recently presented analytic discrete variable representation (DVR) [D.T. Colbert and W.H. Miller, J. Chem. Phys. 96, 1982 (1992)] that facilitates calculations. This might prove particularly useful to spectroscopists, allowing a check of the quality of potentials produced by inversion methods or the reliable calculation of spectrochemical quantities. © 1995 John Wiley & Sons, Inc.
Extension of the Coulomb–Hole–Hartree–Fock theory to molecules
Authors: De Windt Laurent , Hofman Detlef W. M. , Pisani Lorenzo , Clementi Enrico 
Published: January 2005

AbstractThe Coulomb–Hole–Hartree–Fock method introduced by E. Clementi in the early 1960s and reparametrized more recently by S. Chakraworty and E. Clementi to compute the correlated electronic energy in atomic systems, is here extended to compute molecules. The new parametrization is obtained empirically by fitting first and second atomic ionization potentials from He to Ca and a few diatomic molecules. The present formulation makes use of either one or more determinants in order to ensure proper dissociation products, following the early proposal of G.C. Lie and E. Clementi in the context of density functional computations for molecular systems. The new formulation is tested against the dissociation energies of a large number of molecules and it is found satisfactory. © 1995 John Wiley & Sons, Inc.
A discrete look at localization
Authors: Hall G. G. , Rees D. 
Published: January 2005

AbstractThis article introduces a set of localized orthonormal functions to serve as basis functions for quantum calculations. They are defined to be eigenfunctions of the position operator in a function space. Their properties, including their variances, for a one‐dimensional system are developed. The application to simple harmonic motion is considered as an example and, in particular, the time evolution of an initially localized function is calculated and shown to be periodic. The theory can be interpreted as producing a discrete quantization of space with Hamiltonian interactions that are predominantly between nearest neighbors. These functions can also be used in approximate calculations. To illustrate their accuracy, the example of a Morse oscillator treated as a perturbation of a harmonic oscillator is reconsidered. It is shown that the localized functions in a variational calculation lead to a result that is a good approximation for the lowest states. Furthermore, the use of a wave function that is defined only at discrete points can be justified as the first approximation to this, so that its accuracy can also be discussed. © 1995 John Wiley & Sons, Inc.