Dispersion coefficients for polarizabilities and first and second hyperpolarizabilities using full configuration interaction theory

Dispersion coefficients for frequency-dependent properties can efficiently be calculated from the derivatives of the properties with respect to their frequency arguments. We have derived and implemented analytic expressions f or the second-order dispersion coefficients of second-, third-, and fourth- order properties in full configuration interaction (FCI) linear, quadratic, and cubic response theory. The accuracy of the second-order dispersion exp ansion is investigated for BH and Ne for CCSD and FCI. Pade approximants im prove the results. The deviation from the analytic results is, in most case s, less than that between CCSD and FCI. The sensitivity of the dispersion c oefficients to the choice of wavefunction model and basis set is found to b e significant. (C) 1999 Elsevier Science B.V. All rights reserved.