Showing papers by "Yasuyuki Ishikawa published in 1991"
TL;DR: The implementation of the matrix Dirac-Fock-Breit self-consistent-field procedure is presented for Gaussian-type basis sets that show no near-linear dependency problem and has the advantage over the finite-difference approach that it does not complicate the self- Consistent- field procedure in basis-set expansion calculations.
Abstract: The self-consistent-field treatment of the frequency-independent Breit interaction is reviewed with applications to many-electron atoms. The implementation of the matrix Dirac-Fock-Breit self-consistent-field procedure is presented for Gaussian-type basis sets that show no near-linear dependency problem. The matrix Dirac-Fock-Breit procedure has the advantage over the finite-difference approach that it does not complicate the self-consistent-field procedure in basis-set expansion calculations. Basis sets of even- and well-tempered Gaussian functions were used to expand the large and small components of Dirac four-spinors. Expressions are derived for evaluating the matrix elements of the Dirac-Fock-Breit equations. Calculations done on rare-gas atoms He, Ne, Ar, Kr, and Xe and alkaline-earth metals Be, Mg, Ca, and Sr are presented.
67 citations
TL;DR: In this paper, second-and third-order Coulomb correlation corrections were computed by systematically enlarging the virtual space, and the contracted Gaussian basis sets used in the many-body study were designed to retain flexibility for correlated calculations both in the core and the valence region.
7 citations
TL;DR: In this article, the nonvariational method proposed previously for the solution of the momentum-space Schrodinger equation is applied to the ground and various excited states of one-electron heteronuclear diatomic systems.
Abstract: The nonvariational method proposed previously for the solution of the momentum‐space Schrodinger equation is applied to the ground and various excited states of one‐electron heteronuclear diatomic systems. Detailed numerical results are reported for 34 electronic states of the HeH2+ system. The method is demonstrated to give highly accurate electronic energies for heteronuclear systems as for the case of the homonuclear H+2 system.
6 citations
01 Jan 1991
TL;DR: The majority of relativistic electronic structure calculations on atoms and ions have been done using finite difference numerical methods (Desclaux, 1973; Grant et al., 1980) as discussed by the authors, and effective means have been devised for augmenting them to account for correlation effects by, viz., multiconfiguration expansion and many body perturbation theory (MBPT) techniques.
Abstract: The majority of relativistic electronic structure calculations on atoms and ions have been done using finite difference numerical methods (Desclaux, 1973; Grant et al., 1980). They will remain important, especially in atomic calculations, because effective means have been devised for augmenting them to account for correlation effects by, viz., multiconfiguration expansion and many-body perturbation theory (MBPT) techniques.
1 citations
TL;DR: In this paper, the rotational state population distributions of nascent photofragments from the photodissociation of polyatomic molecules have been implemented with the use of the kinematic distribution function developed by Chen and Pei.
Abstract: A general procedure to evaluate the rotational state population distributions of the nascent photofragments from the photodissociation of polyatomic molecules has been implemented with the use of the kinematic distribution function developed by Chen and Pei [Chem. Phys. Lett. 124, 365 (1986)]. Numerical evaluations of rotational state population distributions of diatomic photofragments from photodissociation of the general class of triatomic molecules are presented. The calculated rotational state population distributions are compared with the most recent experimental data on OH and SH photofragments to obtain the information on the kinematic aspects of the photodissociating H2O and H2S molecules.
TL;DR: In this article, the authors performed relativistic self-consistent field (SCF) calculations on a number of neutral and ionized atoms with basis sets of contracted and uncontracted Gaussian-type functions.
Abstract: Relativistic self-consistent field (SCF) calculations have been performed on a number of neutral and ionized atoms with basis sets of contracted and uncontracted Gaussian-type functions. Both Dirac-Fock and Dirac-Fock-Breit SCF calculations have been performed with the intent of observing to what extent basis set contraction affects the calculated relativistic and Breit interaction contributions to total atomic energy. It is found that extensive basis set contraction has relatively little effect on the calculated relativistic and Breit interaction energies.
01 Jan 1991
TL;DR: In this paper, a basis set of Gaussian type functions (GTFs) is used to represent the region very near the nucleus of a molecule for the purpose of self-consistent field and correlation correction procedures.
Abstract: Most electronic structure calculations on molecules are done with basis sets of Gaussian type functions (GTF). Multicenter integrals over GTF are easily evaluated. However, Gaussians behave correctly at neither short nor long range; longer expansions in GTF than in exponential functions are required to attain similar accuracy. Much of the additional length is due to functions added simply to represent the region very near the nucleus. Primitive functions which represent this region may be grouped for the purpose of self-consistent field (SCF) and correlation correction procedures; the grouping is known as contraction. Contraction reduces integral storage requirements and time needed for SCF and post-SCF steps. Extensively characterized sets of contracted GTF for molecular calculations (Dunning and Hay, 1977; Wilson, 1987) exist.