A QM/MM/continuum model for computations in solution:: Comparison with QM/MM molecular dynamics simulations

We propose a model for fast quantum mechanical computations of molecules and processes in solution. The chemical system is described quantum mechanically (QM) using density functional theory A few discrete solvent molecules are described using molecular mechanics (MM) force fields. The bulk solvent is described through a dielectric continuum model. The interaction between the QM/MM aggregate and the continuum is computed by using a multipole moment development of the charge distribution of the former. This is an intermediate model between the standard continuum approach and the combined quantum mechanics and molecular mechanics (QM/MM) technique, in which a large number of MM solvent molecules is considered and a statistical simulation of the solution is performed. The method may also be used to estimate long-range interactions in combined QM/MM Monte Carlo or molecular dynamics simulations. (C) 2001 John Wiley & Sons, Inc.