Correlated frequency-dependent polarizabilities and dispersion coefficients in the time-dependent second-order Mّller-Plesset approximation

A new method for the calculation of correlated frequency-dependent polarizabilities by the use of time-dependent second-order Mّller-Plesset perturbation theory is presented. Within this method the dynamic polarizabilities are defined as second derivatives of the MP2 energy with respect to the strengths of two oscillating external fields. This definition assures the symmetry of mixed polarizabilities and leads to the same second-order pole structure as the diagrammatic double-perturbation MBPT methods. As a derivative method this approach becomes equivalent to finite field MP2 calculations in the static limit. We report applications to helium and neon.