Computational Evaluation of Optical Nonlinearities: Quantum Chemical Approaches

Significant advancement of reliable computational techniques for calculations of nonlinear optical properties of molecules has been achieved in the last two decades. In particular, this is the case for calculations of the first- and second-order hyperpolarizablities implemented in numerous quantum chemical packages. Resonant properties such as two-photon and three-photon absorption have been implemented in only few of them. The inclusion of the influence of the environment on NLO properties has been also achieved. For evaluation of nonlinear response of molecular systems, two different approaches can be employed: the analytic response theory which is more rigorous and sum-over-states (SOS) methods, both based on perturbation theory. Within these approaches, the various methods with different quality of accuracy of electronic excited states can be used.