CONVERGENCE OF PERTURBATION EXPANSIONS AROUND NONSTANDARD MEAN FIELDS

We investigate the convergence of Mo?ller-Plesset Goldstone perturbation-theory expansions around the g-Hartree, Hartree-Fock, and scaled Hartree-Fock mean fields for quantum-chemical models of the beryllium atom and the lithium hydride molecule. We use a finite Hilbert space of many-electron functions constructed from a finite Gaussian basis set of atomic orbitals. In this space it is possible to diagonalize the nonrelativistic Hamiltonian exactly and to calculate perturbation expansions in high order. Our results show significantly faster convergence for perturbation expansions around the g-Hartree mean fields in a large range of the mean-field parameter. © 1990 The American Physical Society.