Relativistic effective potentials in quantum Monte Carlo calculations

Abstract

Abstract This is the first of three papers,0 each from a different group, to report the use of effective potentials, model potentials, or pseudopotentials in QMC calculations in 1987 and 1988. The authors point out the advantages of eliminating core electrons in order to simplify the calculations, reduce the number of singularities in the wavefunction, and thereby reduce the variance in local energies. They note the primary difficulty in using relativistic effective potentials is the nonlocal character of most potentials and their dependence on angular projection operators rather than on mere electron configurations. In this study, the authors defined a simple local potential V in terms of the nonlocal effective potentials operating on a trial wavefunction. The extent of the error introduced was unknown but possibly small. The effective potentials were taken directly from earlier analytic studies for the species considered. The trial wavefunctions were single determinants of Gaussian orbitals together with Jastrow correlation terms. Calculations were carried out for Li/Li- and K/K- so that electron affinities could be obtained. The values so determined were 0.56 and 0.52 eV, respectively, compared to 0.618 and 0.502 eV determined in experiments. It was noted that corresponding all-electron calculations for the F /F- pair required a vastly greater computation effort, perhaps more than a factor of 1000 greater.