The non-empirical calculation of second order molecular properties by means of effective states

Abstract

A method is presented for the efficient calculation of second order (multipole) properties. A complete spectrum (including the continuum) is represented by a small number of effective states. Relations with several existing techniques, such as Padé approximants and generalized Gaussian quadratures, are discussed. The method is applied to time-dependent Hartree-Fock calculations of dynamic multipole polarizabilities and dispersion interactions. For He, Ne, H₂ and N₂ effective spectra are presented which yield dispersion coefficients for the ten possible Van der Waals dimers within 1·2, 3·9 and 6·4 per cent of the full TDCHF C ₆, C ₈ and C ₁₀-coefficients, respectively. These effective spectra are useful if knowledge of Van der Waals surfaces and dynamic polarizabilities is required to interpret experimental data.