Chemia kwantowa w molekularnej optyce nieliniowej

We review quantum-chemical methodologies based on simple two- and three- state models for molecular hyperpolarizabilities and two-photon cross-sections. In this article we show that simplified few-state models, obtained from sum -over-states formalism, are important tools for investigations structure-property relationships for various type of đ-conjugated compounds. These relationships are important for rational design of molecules with large nonlinear optical response