An efficient quantum mechanical/molecular mechanics Monte Carlo simulationof liquid water

An efficient implementation of a quantum mechanical/molecular mechanics (QM /MM) Monte Carlo (MC) simulation of liquid water is presented. The auto-cor relation function of the energy is used to reduce the number of QM calculat ions during the simulation. The effects of the liquid structure on the dipo le moment of the quantum water molecule is considered. Using only 80 QM cal culations at the Hartree-Foc/6-31+ +G(d,p) level but on statistically nearl y uncorrelated structures, we find an average dipole moment for the liquid water of 2.73 +/- 0.13 D. This corresponds to an induced dipole moment of 0 .44 +/- 0.13 D on going from the gas phase to the liquid phase, in excellen t agreement with previous, more extensive computational procedures. (C) 200 1 Elsevier Science B.V. All rights reserved.