ON THE CALCULATION OF THE HYPERPOLARIZABILITIES OF ORGANIC-MOLECULES BY THE SUM OVER VIRTUAL EXCITED-STATES METHOD

The version of time-dependent perturbation theory commonly used in the calculation of the hyperpolarizabilities of organic molecules through an expansion over electronic excited states is briefly rederived by a direct method, simplified for application to the nonresonant case. The application of the method within the framework of semiempirical quantum theory and singly and doubly excited configuration interaction is described. A particular parametrization of the CNDO/S method (CNDO/VS) that has been successful in estimating molecular beta-values for polar aromatic molecules is reviewed. Applications of the method to the interpretation of the molecular and crystal second-order properties of 2-(alpha-methylbenzylamino)-5-nitropyridine (MBANP) and to the calculation of the gamma-tensor for various types of conjugated compounds are given.