Accurate dipole moments from Hartree-Fock calculations by means of class IV charges

Charge Model 2 (CM2) is parameterized for Hartree-Fock calculations with th e correlation-consistent polarized valence double zeta (cc-pVDZ) basis set. The resulting charge model has an RMS error of 0.18 D over a training set of 198 polar molecules. The charge model is additionally applied to 8 nucle ic acid bases and methyl azide to test its performance for nitrogen-contain ing compounds not found in the training set. The results demonstrate that t his new CM2 model based on ab initio Hartree-Fock calculations is robust in predicting the charge distributions of such molecules. Comparison of CM2 r esults for the nitrogen-containing test set with those from a previous char ge model, charge model 1 (CM1) based on AM1 (Austin model 1) and PM3 (param eterized model 3) wave functions, indicate that the CM2 charges are more ac curate than those from the previous model. (C) 1999 American Institute of P hysics. [S0021-9606(99)30125-2].