Chem. Phys. Lett. 307, 235-243 (1999).
Received 24 March 1999; in final form 28 April 1999
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 for 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 expansion is investigated for BH and Ne for CCSD and FCI. Padé approximants are found to improve the results. The deviation from the analytic results is in most cases less than that between CCSD and FCI. The sensitivity of the dispersion coefficients to the choice of wave function model and one-electron basis set is investigated and found to be significant.
*Corresponding autho. E-mail: helena@kemi.aau.dk
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