Reduced dipole pseudospectra for the accurate tabulation of C6 dispersion coefficients

Abstract

The possibility of tabulating accurate reduced dipole pseudospectra of single molecules is of great importance for obtaining reliable dipole dispersion constants from which C6 dispersion coefficients can be derived for all possible interacting pairs. Use of an efficient interpolation procedure allows to obtain dispersion constants from analytical integration of the Casimir–Polder integral over the product of frequency-dependent polarizabilities (FDPs) at imaginary frequencies. FDP calculations can then be done at a few selected frequencies, so overcoming at a time the difficulties arising from numerical quadratures and sensibly reducing the computational demand. In the static case, appropriately reduced n-term pseudospectra are obtained by forcing in an optimal way large N-term extended pseudospectra to be converted to FDPs using the same interpolation technique. Calculations performed at the eight frequencies arising by choosing n = 4 (four-term approximation) in the optimized interpolation procedure, give reduced dipole pseudospectra from which isotropic C6 dispersion coefficients and γ6 anisotropy coefficients are obtained in almost perfect agreement with the result of the most accurate data available from the literature and of recently proposed variational techniques.