ATOMIC CHARGES OF THE WATER MOLECULE AND THE WATER DIMER

Atomic charges in the water molecule and the water dimer have been cal culated by two different schemes for partitioning the total charge dis tribution: Mulliken charges and atomic polar tenser-based charges. Lar ge-scale calculations have been carried out where the basis set has be en increased systematically toward the basis-set Limit. The Mulliken c harges are highly sensitive to the choice of basis, and no convergence is observed. In contrast, atomic charges obtained from the trace of t he atomic polar tensor exhibit rapid basis-set convergence. We have al so investigated the effects of electron correlation on the atomic char ges of the water molecule. Finally, the polarization and charge-transf er effects on the atomic charges have been calculated for the water di mer. The importance of such terms in a water potential used in molecul ar dynamics simulations of aqueous solutions is discussed.