Momentum space and Coulomb correlation: A two-particle density analysis for the H2(1Σ+g) molecule

Abstract

Electron correlation in momentum space is assessed for the ground-state of H2 by examining changes in the two-particle probability density evaluated over preselected momentum planes. The associated radial and angular ‘‘planar Coulomb shifts,’’ ΔR(p12) and ΔA(εp), are also calculated. This study complements an earlier analysis for H2 in position space. The natural expansion of the correlated wave function used previously was converted into momentum space by means of a Dirac–Fourier transform. As before, correlation effects are measured with respect to the description provided by the first natural configuration. Characteristics of the three components of Coulomb correlation for a linear molecule are highlighted by specific choices for the momentum of a ‘‘test’’ or ‘‘reference’’ electron. Unlike position space, it was found that one component worked in distinct opposition to the other components, a feature analogous to atomic studies in momentum space. The trends observed throughout a series of probability changes in momentum space for H2 were rationalized and linked to the correlation behavior in position space.