A. Rutkowski et al., EFFECTIVE HAMILTONIAN FOR NEAR-DEGENERATE STATES IN RELATIVISTIC DIRECT PERTURBATION-THEORY - II - H-2(-LIKE SYSTEMS()), The Journal of chemical physics, 109(6), 1998, pp. 2135-2143
The recently developed effective Schrodinger-like Hamiltonian equation
(EHA) in a model space of near-degenerate nonrelativistic two-compone
nt spinors is applied to the relativistic energy corrections at first,
second, and third order of c(-2) within the framework of relativistic
direct perturbation theory (DPT). The dominant singular part of the t
otal relativistic correction is already recovered by the lowest-order
effective Hamiltonian in the spirit of degenerate perturbation theory,
while the perturbative expansion needs to account for only the small
remaining part. Numerical results for groups of excited potential curv
es of the one-electron H-2(+)-like quasimolecule Sn-2(99+) are present
ed and discussed. In general the most efficient approach is first-orde
r EHA-DPT for the set of states, followed by single-state DPT of highe
r orders. (C) 1998 American Institute of Physics.