Atomic orbital populations and atomic charges from self-consistent field molecular orbital wavefunctions

Atomic orbital populations, obtained by partitioning the electrons within a molecular orbital in proportion to the squares of the atomic orbital coefficients, are shown to avoid the two major deficiencies of the Mulliken population analysis, namely, orbital populations greater than two and less than zero. Within a series of molecules, our method, which is a modification of the method due to Christoffersen and Baker and is referred to as the MCB method, leads to similar chemical trends as the conventional Mulliken approach. With the core populations frozen at two, the MCB method shows an approximately linear relationship between the charge on a hydrogen atom and the electronegativity of the first-row atom in the binary hydrides. For the same series of molecules, the MCB atomic charges correlate linearly with atomic charges obtained by integration of the charge density ρ(r) over regions of space defined by the gradient vector field.