Charge distributions and chemical effects. XXXVI. Charge analysis involving configuration interaction: application to alkanes

Abstract

An analysis of atomic charges is presented for simple alkanes. Basically, Mulliken's scheme is followed, except for the partitioning of CH overlap populations. This achieves a relative ordering of atomic charges which is independent of the basis sets used in abinitio calculations. The absolute magnitude of atomic charges, however, is basis set dependent. Extensive geometry and scale factor optimizations yield the following results (in 10−3 e units) for the carbon net charge in ethane: 69.4 (STO-3G), 55.1 (STO-3G + CI), 42.8 (4-31G), and 37.8 (4-31G + CI). It appears that charge analyses converge toward the empirical result, 35.1 × 10−3 e, provided they are carried out after configuration interaction involving reasonably large optimized basis sets.