Electronic polarization of a water molecule in water. A combined quantum chemical and statistical mechanical treatment

The polarization of an ab initio quantum chemically described water molecule due to the surrounding statistical mechanical Monte Carlo water bath is studied. The quantum chemically described water molecule is surrounded by 89 statistically described water molecules situated in a spherical cavity in a dielectric continuum. The total interaction between the quantum chemically described water molecule and the total surroundings is on average 0.5 kJ/mol larger than for the interaction for a classically described water molecule. This increase is despite the fact that the potential function used between the quantum chemically described water molecule and a classical water molecule is almost identical to the potential between the classical molecules. The difference is due mainly to the polarization of the quantum chemically and the classically described water molecules.