Ab initio calculations of multipole moments, polarizabilities and isotropic long range interaction coefficients for dimethylether, methanol, methane, and water

Multipole moments, up to and including 1= 6, and multipole polarizabilities up to and including I + I’ = 6, have been calculated, for the molecules dimethylether, methanol, methane and water, from LCAO-SCF wavefunc-tions using an AO basis set of DZ quality augmented with double d-polarization functions at the non-hydrogen-, and p-polarization functions at the hydrogen atoms. The polarizabilities were obtained using Rayleigh-Schrödinger perturbation theory and the non-empirical Unsold method. The long range isotropic coefficients, C₆, C₈, and C₁₀ have been calculated for all ten types of interactions between the four molecular species. For the interaction between like molecules an effective C6 coefficient has been derived for comparison with experiment. The agreement between calculated values and experimental data, as far as available, is satisfactory.