Correlation Effects in Atoms. I. Helium

Abstract

The variational-perturbation method has been applied to the study of correlation effects in the helium atom. Starting from the Hartree-Fock Hamiltonian as zeroth-order approximation, we have evaluated the correlation energy through fifth order in perturbation theory. With a ten-parameter trial wave function we get ${E}_{\mathrm{corr}}=\ensuremath{-}0.0419$ atomic units, which differs from the exact value by 0.4% and shows the rapid convergence of this type of Hartree-Fock perturbation theory. Comparison is also made with similar calculations using Hartree or hydrogenic Hamiltonians as starting points.