Charge-dependent basis sets. I. First row elements

The effects of the molecular environment on the atomic orbital (AO) exponen ts have been taken into account by varying them with the electronic populat ion. The dependence of these AO exponents was described by a quadratic equa tion involving the net atomic charges or the individual AO populations. The se AO exponents were allowed to vary within the range defined by the AO exp onents of the cation and anion atomic species. The atomic charges and AO po pulations were calculated by the Mulliken and the Lowdin population analysi s approaches. Several molecules (HCN, HNC, CH3F, CH3OH), molecular anions ( OH-, NH2-, N-3(-), NO2-), and chemical reactions (HCN --> HNC; F- + CH3OH - -> FCH3 + OH-) were used to test this charge-dependent approach for basis s ets. Very significant differences were obtained for the anionic systems (mo lecules and transition states) when the charge-dependent and charge-indepen dent basis sets were employed. (C) 1999 John Wiley & Sons, Inc.