DFT study of polarizabilities and dipole moments of water clusters

Density functional theory (DFT) calculations with different exchange-correlation functionals, Becke's three-parameter exchange functional and the gradientcorrected functional of Lee, Yang, and Paar (B3LYP) and Becke's three-parameter functional with Perdew-Wang correlational functional (B3PW91), are performed to study the dielectric properties of small and medium-sized water clusters. For these H-bonded systems, we optimize the geometries and compute the dipole moments and polarizabilities using a supermolecule approach. The corresponding properties of the individual water molecules in the clusters are extracted from the molecular properties using the Hirshfeld expansion of the electronic density. Calculations at Hartree-Fock and second-order Moller-Plesset (MP2) levels are also presented for a comparison with the DFT results. The dependence of the dielectric properties on the cluster structure and size is given for both clusters and individual molecules and is compared with the available experimental data. The intermolecular interactions and their influences on the dielectric properties are discussed. The current results could serve to improve existing polarizable force fields for water. (C) 2004 Wiley Periodicals, Inc.