Behavior of the APSG electronic wavefunction near the electron‐electron coalescence point

Abstract

AbstractThe behavior of electronic wave functions within the antisymmetrized product of strongly orthogonal geminals (APSG) approximation at the point of the electron‐electron coalescence is examined. Its elucidation allows one to understand the origins of the previously reported satisfactory performance of APSG wavefunctions as reference states in the connected moments expansion method (CMX). It is shown that the failure to satisfy the electron‐electron cusp condition causes divergence of certain type of integrals that enter the CMX formulae, which in turn brings about significant deterioration of the quality of the resulting estimates for the ground‐state energy in finite basis sets.