A COUPLED DENSITY FUNCTIONAL-MOLECULAR MECHANICS MONTE-CARLO SIMULATION METHOD - THE WATER MOLECULE IN LIQUID WATER

A theoretical model to investigate chemical processes in solution is d escribed. It is based on the use of a coupled density functional/molec ular mechanics Hamiltonian. The most interesting feature of the method is that it allows a detailed study of the solute's electronic distrib ution and of its fluctuations. We present the results for isothermal-i sobaric constant-NPT Monte Carlo simulation of a water molecule in liq uid water. The quantum subsystem is described using a double-zeta qual ity basis set with polarization orbitals and nonlocal exchange-correla tion corrections. The classical system is constituted by 128 classical TIP3P or Simple Point Charge (SPC) water molecules. The atom-atom rad ial distribution functions present a good agreement with the experimen tal curves. Differences with respect to the classical simulation are d iscussed. The instantaneous and the averaged polarization of the quant um molecule are also analyzed. (C) 1996 by John Wiley & Sons, Inc.