Calculation of Intermolecular Interaction Energies by Direct Numerical Integration over Electron Densities. 2. An Improved Polarization Model and the Evaluation of Dispersion and Repulsion Energies

Abstract

A procedure to adapt electron densities of isolated molecules for the evaluation of intermolecular energies, first introduced in paper 1 (Gavezzotti, A. J. Phys. Chem. B 2002, 106, 4145) is here improved for polarization energy and extended to dispersion and repulsion terms. Dispersion is evaluated from atomic polarizabilities distributed over the electron density, using an average ionization potential taken as the energy of the highest occupied molecular orbital, in a London-type inverse sixth-power formulation. Repulsion is evaluated from the overlap between electron densities. The method, called semiclassical density sums (SCDS), requires only four disposable numerical parameters and allows a complete evaluation of intermolecular interaction energies for a rather wide range of molecular systems. Calculations on molecular dimers, in comparison with results obtained by high-level quantum chemical methods, show that SCDS energies are quite reliable, at a fraction of the computational cost. The sublimation...