Effect of electron correlation on the topological properties of molecular charge distributions

Abstract

This paper reports on the effect of electron correlation on the topological properties of the charge density and its associated gradient vector and Laplacian fields. The properties of these fields define the atoms, their reactivity, and the structure of a molecular system within the theory of atoms in molecules. The singlet and triplet states of CH2, CF2, and SiH2 are investigated using a configuration interaction method which includes all single and double excitations with respect to suitable zero-order reference wave functions, together with a number of hydrocarbon molecules including unsaturated and geometrically strained systems for which the correlation is introduced via the generalized valence bond approach. It is found that the correlated charge distributions possess the same number and kind of critical points in both the ρ(r) and ∇2ρ(r) fields as are found for SCF charge distributions. Thus the topology of a charge distribution and the structure it defines are unaffected by the addition of Coulomb correlation. The quantitative changes in the properties of the charge density at the critical points in both ρ(r) and ∇2ρ(r) induced by correlation are found to be small in magnitude and to be more pronounced for shared or covalent atomic interactions than for systems with pronounced charge transfer between the atoms. The properties of the atoms in these molecules also exhibit correspondingly small changes in value.