Charge model 4 and intramolecular charge polarization

Partial atomic charges provide the most widely used model for molecular charge polarization, and Charge Model 4 (CM4) is designed to provide partial atomic charges that correspond to an accurate charge distribution, even though they may be calculated with polarized double-ζ basis sets with any density functional. Here we extend CM4 to six additional basis sets, and we present a model (CM4M) that is individually optimized for the M06 suite of density functionals for ten basis sets. These charge models yield class IV partial atomic charges by mapping from those obtained with Löwdin or redistributed Löwdin population analyses of density functional electronic charge distributions. CM4M/M06-2X/6-31G(d)//M06-2X/6-31+G(d,p) partial atomic charges are calculated for ethylene, CH_nCl_4-n (n = 0-4), benzene, nitrobenzene, phenol, and fluoromethanol and used to discuss gas-phase polarization effects.