Generalized self-consistent reaction field theory in a multicenter-multipole ab-initio LCGO framework. I. Electronic properties of the water molecule in a Monte Carlo sample of liquid water molecules studied with standard basis sets

A generalized reaction field theory of surrounding medium effects on the electronic wavefunction of a solute is implemented at an ab initio level of theory. The reaction field (RF) potential, which in the exact theory is given as a compact functional form factorized into a solute charge density and a RF susceptibility, is calculated at a multicenter multipolar level of approximation. The static reaction field potential response function depends on the geometry and on the polarizability response tensor of the surrounding medium. The scheme is well adapted to study electronic systems in structurally fluctuating environments when these latter are simulated either with molecular dynamics or by Monte Carlo techniques. For nonhomogenous media, such as the environments around a water molecule immersed in a sample of equilibrated water molecules, a permanent electrostatic potential is also present. Solvent effects on one water molecule produced by a MC sample of water molecules interacting via MCY water-water potential and previously equilibrated have been studied at the RHF SCF level with STO-3G, 4-31G, 4-31G** and 6-31G** basis sets. Fluctuations of Mulliken populations, dipole moments, permanent solvent potentials and reaction potential components are studied for these 4 basis sets.