Frequency-dependent hyperpolarizabilities in the coupled-cluster method: the Kerr effect for molecules

Introducing frequency dependence in the equation-of-motion coupled-cluster method, we evaluate the optical Kerr effect for butadiene and ammonia. This permits a critical evaluation of dispersion estimates via the uncorrelated time-dependent Hartree-Fock theory. The percentage dispersions are similar for low frequencies, but not for larger values. We also consider other dispersion estimates based upon a power series expansion in the frequency. This leads to a possible resolution of the observed discrepancy between correlated theory and experiment for butadiene. Augmented by vibrational corrections, we offer estimates for the experimentally unknown Kerr values for NH3 and C4H6.