The electronegativity equalization method II: Applicability of different atomic charge schemes

The amenability of different schemes for the calculation of atomic charges in the electronegativity equalization method (EEM) is investigated. To that end, a large training set of molecules was composed, comprising H, C, N, O, and F, covering a wide range of medicinal chemistry. Geometries are calculated at the B3LYP/6-31G* level. Atomic charges are calculated using five different methods, belonging to different types of population analysis. Effective electronegativities and hardness values are calibrated from the different quantum chemically calculated atomic charges. The resulting quality of EEM charges is investigated for the different types of atomic charge calculation methods. EEM-derived Mulliken and NPA charges are in good agreement with the ab initio values, electrostatic potential derived, and Hirshfeld charges show no good agreement.