Many-body interactions calculated with the direct reaction field model

The direct reaction field (DRF) model was developed for calculations of ele ctronic properties of molecules in the condensed phase. In the DRF approach the electrons of (part(s) of a system is described with wavefunctions, the larger parts classically with point charges and polarizabilities. Leaving out the quantum-mechanical part(s) leads naturally to a polarizable force f ield. In this paper we demonstrate the usefulness of the DRF model for the study of many-body interactions in polar systems. We have calculated the ma ny-body interactions in clusters of HF, H2O and urea in our classical polar ization model and compared the results to ab initio calculations using larg e basis sets. We find that the results obtained using the classical model c ompare excellently to ab initio results. (C) 1999 Published by Elsevier Sci ence B.V. All rights reserved.