bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular correlation integrals. Two center one electron integrals containing a function of interparticle distance in one center expansion approximation
Authors: Joshi Bhairav D. , Kapoor K. L. 
Published: December 2004

AbstractTwo‐center one‐electron integrals needed in certain molecular correlated wave function calculations, using one‐center expansion approximation, have been studied. The form of the basic correlated function used in this study is

The parent integral is expressed in terms of an angular integral, and an auxiliary radial integral depending upon the variables r1, r2, and r12. Several analytical formulas, and a recursive formula are derived for the auxiliary integral, and other related integrals. All these formulas are given in computationally useful forms. Logical flow charts and FORTRAN programs were constructed for computing the basic integrals discussed in the paper. Numerical values of some integrals, thus obtained, are tabulated for comparisons.
Semiempirical approach to the problem of the radiative lifetime of the excited F‐color center
Authors: Berezin A. A. 
Published: December 2004

AbstractIt is emphasized that for the theoretical consideration of many problems of defect centers in crystals (especially of problems which need the correct asymptotic behavior of the wave functions) the semiempirical approach can be effective. As an example the spontaneous radiative time decay of the excited F‐center in alkali halides is calculated by using the experimental energies of absorption and emission bands.
Etudes en méthode de Hartree‐Fock avec projection … II. La fonction d'onde exacte d'un système de deux electrons dans un etat 1S comme projection d'un déterminant de Slater
Authors: Prat R. F. , Lefebvre R. 
Published: December 2004

AbstractThe ground state wave‐function of a two electrons atom may be represented to any accuracy by a 1S projected Slater determinant built on hypercomplex spin‐orbitals.
The distribution of electronic charge in the ground state of cubic boron nitride
Authors: Doggett G. 
Published: December 2004

AbstractThe distribution of electronic charge in cubic boron nitride is investigated using the bond orbital wave functions recently calculated by Coulson and Doggett. Plots of the one‐electron density function, in the (110) plane, are found to be insensitive to the choice of atomic basis functions, in contradistinction to the previously calculated effective atomic charges. A number of structure amplitudes are also calculated for each of the bond orbital wave functions.
Symmetry effects in the radiation damping of degenerate states
Authors: Craft Lawrence N. 
Published: December 2004

AbstractRadiation damping of three atoms in a radiation field is studied for both a linear and closed‐chain configuration. One atom of the system is initially excited. Use is made of the Heitler‐Ma perturbation procedure up to second order. The discussion is developed in terms of the symmetry of the interactions within the system. The interactions arising from dipole transitions perpendicular to the plane of the closed chain are shown to be similar to the interactions in a two‐atom system, and the results are extended to cover larger rings.
Wellenmechanische absolutberechnung schwingungsspektroskopischer daten am äthylen
Authors: Swanstrøm P. , Janoschek R. , Preuss H. 
Published: December 2004

AbstractThe ethylene molecule has been investigated by means of the General SCF–MO–LC(LCGO) Program System for 12 different nuclear positions, taking all electrons into account. The equilibrium distances and angles as well as all force constants of the totally symmetric vibrations with the corresponding frequencies have also been calculated.
Fermi surfaces and electron–impurity interactions in simple metals
Authors: Foster Howard J. 
Published: December 2004

AbstractA review is given of the current status of our work on electron transport properties and Fermi surfaces in simple metals. A simple classical model is proposed to extend existing theory to account for the effects of electron‐impurity interactions on the behavior of magnetoacoustic absorption and the size and shape of the Fermi surface in the alkali metal potassium. The theoretical prediction is compared with measurements of the magnetoacoustic absorptionand Fermi surface diameters in potassium crystals of different impurity levels. An attempt is made to explain, on the basis of the theory of electron–impurity interactions, the decrease by 9% in the Fermi diameter and the departure by 53% in the phase factors of the impure potassium crystal. The results are compared with observations on a zone refined potassium crystal which satisfies the nearly‐free‐electron model.
Mirror reflection symmetry and the phase relations for partially and almost filled shells of equivalent atomic electrons
Authors: Jucys A. P. , Rudzikas Z. B. , Savukynas A. J. 
Published: December 2004

AbstractThe mirror reflection symmetry which consists in the correlation of the substitution j → −j −1 with the reflection of the coordinate system and of m → −m with the reflection of the space with respect to the xy‐plane has been applied to the quasi‐spin formalism. The phases of the wave functions of the shell of equivalent atomic electrons treated as partially filled, as they relate to those when the same shell is treated as almost filled, have been established. The mirror reflection symmetry has been generalized for the supplementary quantum numbers used for distinguishing the terms of the same kind. The phases of the coefficients of fractional parentage of almost filled shell enabling us to determine them from those of partially filled shell have been specified. Corresponding phase relations for the matrix elements of operators have also been considered.
Group‐theoretical methods for determining permitted terms of the electronic states of polyatomic molecules and complexes in MO and HL schemes of calculation. II
Authors: Cherepanov V. I. , Shchetkov A. A. , Farberov D. S. , Men A. N. 
Published: December 2004

AbstractGroup‐theoretical methods for determining permitted terms of electrons in polyatomic molecules and complexes in the MO and HL methods are proposed. Essentially, the permutational symmetry of the electron system is utilized. Some concrete examples of the operation of these methods are considered.
All electron calculations of open‐shell polyatomic molecules. III. Perturbation treatment of the spin polarization in vinyl and methyl radicals
Authors: Millié Philippe , Lévy Bernard , Berthier Gaston 
Published: December 2004

AbstractA first order perturbation treatment starting with SCF‐MO'S in canonical or equivalent quasi‐localized form is presented for the hyperfine coupling constants of vinyl and methyl radicals. The spin‐polarisation contribution to hyperfine splittings is found to be large, negative for the proton of the radical center in both radicals and positive for the β protons of vinyl.
Gaussian representations of charge overlap effects in intermolecular forces
Authors: Riera A. , Meath W. J. 
Published: December 2004

AbstractThe ground state HH+ and HH interactions are used as model interactions for investigating the feasibility of using Gaussian basis sets for representing charge overlap effects in intermolecular forces. The non‐expanded charge‐induced dipole energy and the non‐expanded dipole‐dipole dispersion energy, respectively, for these interactions are calculated using two types of Gaussian basis functions to represent the first order wave function, Ψ(1). Very good results for these interaction energies, which include charge overlap effects, are obtained for all interatomic separations by using small Gaussian basis sets to represent the interaction, that is Ψ(1), and/or the isolated atoms (the zeroth order wave function).
Symmetry eigenfunctions suitable for many‐electron theories and calculations. I. Mainly atoms
Authors: Bunge Carlos F. , Bunge Annik 
Published: December 2004

AbstractAn interpretation of degenerate symmetry spaces associated with a given atomic or molecular configuration is presented, and the theory necessary for atomic applications is discussed in detail. Löwdin's symmetric projection operator for spin and orbital angular momentum is applied on a well‐defined sequence of Slater determinants. In this way a degenerate LS space is divided into orthogonal invariant subspaces which can be classified according to internal couplings of angular momentum. A procedure is found which permits expression of each of these LS eigenfunctions as the smallest possible number of successively orthogonalized projected Slater determinants. In particular, minimum size Hartree‐Fock interacting spaces (important in rapidly convergent correlation energy calculations) are obtained in their most compact form. An optimum partition of degenerate spaces of three and four excited (atomic or molecular) configurations is obtained in general. Interpretations, simplifications, and systematizations in atomic configuration interaction calculations are discussed in light of present results.
Structure de l'ion fluoronium FH et chemin de la protonation du fluorure d'hydrogene
Authors: Leibovici Claude 
Published: December 2004

AbstractThe structure of the ion FH is investigated on the basis of semiempirical (INDO) and nonempirical (extended gaussian basis set) calculations. In agreement with experiment, both methods predict that, when going from FH to FH, there is a lengthening of the FH bond; also in agreement with infrared analysis, the calculations indicate a bent structure for the fluoronium ion (valence angle at about 120°). The analysis of the FH protonation path reveals the existence of a potential barrier which is exclusively produced by solvation effects; the dependence of the proton affinity of FH on the dielectric constant of the reaction medium is also discussed.
Dynamic polarizability of helium: A random phase approximation calculation
Authors: Linderberg Jan , Prato Domingo 
Published: December 2004

AbstractThe random phase approximation (RPA) or time‐dependent Hartree–Fock approximation (TDHF) is reconsidered for the calculation of the dynamic polarizability for atoms. An integral equation which admits a simple numerical treatment is established. The asymptotic approximation for the electron propagator is tested for its applicability by means of comparisons with earlier results.
Matrix elements in all valence electron models
Authors: Linderberg Jan , Seamans Lloyd 
Published: December 2004

AbstractModel Hamiltonians for all valence electron calculations are examined with regard to the possibility of obtaining consistent sets of matrix elements for the description of electromagnetic processes such as photon absorption, optical activity, and magneto‐optical activity. Linear and angular momentum and position operator matrix elements are related to Hamiltonian matrix elements through symmetry relations and equations of motions. The possibility of elimination of empirical interatomic matrix elements is studied.
Error analysis of variationally optimized upper‐ and lower‐bound wave functions for H
Authors: Ley Barbara E. , Thorpe Tony , Rothstein Stuart M. 
Published: December 2004

AbstractWave functions which are a linear combination of H‐type elliptical orbitals are optimized to provide either an upper bound or a lower bound to the H ground state. For the latter, Temple's formula is used. Three criteria are considered to determine the relative accuracy of these wave functions: (i) energy (calculated versus exact eigenvalue); (ii) average error; and (iii) local energy. Although the lower‐bound optimized wave functions obtained are the most accurate available for H from approximate wave functions, they are still inferior to the corresponding upper‐bound wave functions by criteria (i) and (ii). In particular, using criterion (ii), it is shown numerically that the upper‐bound functions are “correct to second order,” while the lower‐bound functions are almost, but not quite, “correct to second order.” Despite this, the local energy analysis, criterion (iii), reveals that the lower‐bound wave functions can be more accurate than the upper‐bound functions in some regions of space, and hence give more accurate values for physical properties sensitive to these regions. Examples considered are the dipole–dipole and Fermi contact interactions.
Orthogonalization of overlapping orbitals by optimal polynomials. I. Polynomials constructed from spectral radii
Authors: Ra Øystein 
Published: December 2004

AbstractInverses and inverse square roots of overlap matrices are approximated by polynomials constructed on the basis of an integral transform of the metric resolvent and Kublanovskaya's conformal mapping technique. Given reasonable upper and lower bounds for the support of the overlap matrix spectral distribution, the described expansions have significantly better convergence properties than the well known power series methods, yet retain the simplicity of these schemes.
Convergence behavior of some multiconfiguration methods
Authors: Banerjee A. , Grein F. 
Published: December 2004

AbstractThe optimization scheme of the “multiconfiguration method based on the generalized Brillouin theorem” (MCGBT) has been analysed and found to converge quadratically. Its rate of convergence has been compared with that of other optimization methods such as the first‐order Rayleigh‐Schrödinger perturbation, the steepest descent, the single vector diagonalization, the Newton‐Raphson, and the conventional SCF method. The convergence of the MCGBT scheme has been found to be superior to the convergence of the above mentioned schemes.
Group theoretical classification of states of a molecular system at definite states of its constituent parts
Authors: Kaplan I. G. , Rodimova O. B. 
Published: December 2004

AbstractA method is developed for determining the allowed states of a many‐particle system at definite states of the subsystems (impurity ion complexes in crystals, nucleon clusters in nuclei, polyatomic molecules). The advantage of the method proposed here over those previously developed is that the present one is independent of the number of particles in the subsystems. Depending on the value of spin Sa the subsystems are considered either as bosons or fermions. The representation character expression whose expansion gives all the terms 2s+1Γ(α) with a definite value of total spin of the system is written as the product of permutation and orbital factors. The orbital factor is defined in terms of characters of the local point group representations. Some alternative ways of calculating the permutation factor are discussed: a) with the use of tables of reduction of the unitary transformation group U2Sa+1 in a three‐dimensional rotation group; b) through the plethysm coefficients; and c) in terms of 3nj‐symbols of three‐dimensional rotation group. Some examples of application of the method to various systems are presented.
A survey of some theoretical studies of negative ions
Authors: Simons Jack 
Published: December 2004

AbstractThe quantum chemical methods employed by us to investigate the stabilities, charge densities, and bonding characteristics of atomic and molecular anions are briefly reviewed. The results of our work on chemically interesting species are surveyed, as are our initial results on the treatment of solvation effects in anionic systems. Finally, a simple‐minded approach to the problem of finding shape resonances for electron–atom scattering processes is outlined.
Absorption line shape of two coupled oscillators decaying in two different mediums
Authors: Hardisson A. , Mauricio F. , Velasco S. 
Published: December 2004

AbstractThe linear response theory is used to study the line shape of two coupled oscillators, decaying in two different baths, when one of the oscillators is coupled to the radiation field. The baths are considered to be thermally excited. The analysis is based on the computation of the correlation functions 〈a (t)ai (0)〉 and 〈ai (t)a(0)〉 of each oscillator, taking the coefficients associated with the operators a and ai in the Heisenbemg representation as the starting point of the calculation. The line shape in different cases is also discussed.
Exact eigenvalues for the Coulomb potential with cut‐off
Authors: Linz Peter , Chen Tien Chi 
Published: December 2004

AbstractThe solution of the quantum‐mechanical one‐particle problem involving a Coulomb potential with a cut‐off contains Whittaker functions, difficult to evaluate individually. However, the energy expression involves a ratio of two contiguous Whittaker functions, and the entire ratio is easily expressed as a convergent continued fraction. Representative energy eigenvalues are calculated, correcting the errors due to an earlier Bessel function approximation by Wannier.
Electronic structure of SiH2, PH2, and their positive and negative ions
Authors: Ball John R. , Thomson Colin 
Published: December 2004

AbstractAb initio LCAO‐MO‐SCF calculations on SiH2 and PH2 and their positive and negative ions are reported, using a variety of Gaussian basis sets. The charge distribution, bonding, and molecular properties of these ions are compared with the available experimental data.
Symmetry of nonrigid molecules and isomerization processes
Authors: Gilles J. M. F. , Philippot J. 
Published: December 2004

AbstractStarting from the concept of a totally flexible molecule, rigidity is introduced by restricting progressively the allowed permutations. Each nonrigid isomer is then characterized by its Longuet‐Higgins group ℒ of allowed permutation inversions. For a given ℒ all nonrigidity types correspond to all possible choices of the symmetry subgroup ℒ of the skeleton. The structure of ℒ also allows a characterization of the isomerization processes studied in chemical kinetics. In both situations, isomerization mechanisms may be associated with generators and are, in the simplest situations, represented by Cayley graphs.
Metric‐constrained variation method for atoms and molecules
Authors: Morikawa Tetsuo 
Published: December 2004

AbstractA new method is presented for the variational calculation of a set of vectors under the condition that the metric of the vectors remains unchanged through the process of variation. Application of this method to typical measures (energy, overlap, distance, etc.) in quantum chemistry gives rise to new variational equations, for which the solution yields the Löwdin symmetric orthonormalization, the Kashiwagi–Sasaki generalization, the symmetric deorthogonalization, and the Adams localization, etc.
Many‐body perturbation theory, coupled‐pair many‐electron theory, and the importance of quadruple excitations for the correlation problem
Authors: Bartlett Rodney J. , Purvis George D. 
Published: December 2004

AbstractMany‐body (diagrammatic) perturbation theory (MBPT), coupled‐pair many‐electron theory (CPMET), and configuration interaction (CI) are investigated with particular emphasis on the importance of quadruple excitations in correlation theories. These different methods are used to obtain single, double, and quadruple excitation contributions to the correlation energy for a series of molecules including CO2, HCN, N2, CO, BH3, and NH3. It is demonstrated that the sum of double and quadruple excitation diagrams through fourth‐order perturbation theory is usually quite close to the CPMET result for these molecules at equilibrium geometries. The superior reliability of the CPMET model as a function of internuclear separation is illustrated by studying the 1∑ potential curve of Be2. This molecule violates the assumption common to nondegenerate perturbation theory that only a single reference function is important and this causes improper behavior of the potential curve as a function of R. This is resolved once the quadruple excitation terms are fully included by CPMET.
Beryllium dimer, a critical test case of MBPT and CI methods
Authors: Blomberg Margareta R. A. , Siegbahn Per E. M. 
Published: December 2004

AbstractThe ground‐state potential curve for the beryllium dimer is calculated as a critical test case for methods based on many‐body perturbation theory (MBPT) and configuration interaction (CI). In particular, the recently proposed double excitation (DE) MBPT method is compared to the standard SCF‐CI method including single and double excitations from a single reference determinant. The SCF‐CI method is shown to give surprisingly accurate results compared to more complete CI calculations including a larger configuration space, whereas the DE‐MBPT method breaks down more or less completely, particularly for larger basis sets. The results thus demonstrate the importance of including the renormalization terms in this case. Finally, Davidson's correction and related methods lead to an even more severe breakdown than the DE‐MBPT method.
Universal basis sets and transferability of integrals
Authors: Silver David M. , Wilson Stephen , Nieuwpoort W. C. 
Published: December 2004

AbstractThe concept of a universal basis set for electronic structure calculation is illustrated by presenting results obtained when basis sets are transferred from one atom to another. A single Slater‐orbital basis set, consisting of nine 1s and six 2p functions, produces Hartree‐Fock total energies and orbital energies in good agreement with the most accurate calculations of these energies obtained using different basis sets individually optimized for each atom. Transferability of integrals is a natural consequence of the use of the same basis set for each atom in a molecule.
Theoretical study on the vertical electronic spectrum of carbonyl fluoride, F2CO
Authors: Vasudevan K. , Grein F. 
Published: December 2004

AbstractAb initio self‐consistent‐field (SCF) and configuration interaction (CI) calculations on the ground and excited states of carbonyl fluoride (F2CO) were carried out at its experimental ground‐state equilibrium geometry. Vertical transition energies deduced from the CI results provide assignments for the electronic systems I–IV, experimentally observed by Workman and Duncan. The singlet excited state, 1A1 (π→π*), is found to be a mixed valence–Rydberg state and to he 1 to 1.2 eV above the suggested experimental value, irrespective of the choice of the basis used for the CI calculations.