A quantum mechanical method for calculating nonlinear optical properties of condensed phase molecules coupled to a molecular mechanics field: A quadratic multiconfigurational self-consistent-field/molecular mechanics response method

An approach for determining nonlinear optical properties within a quantum m echanics/molecular mechanics method is presented. The response equations in the multiconfigurational self-consistent-field/molecular mechanics approac h that includes polarization effects are derived and implemented for second order in response theory. The method is employed to calculate frequency-de pendent first hyperpolarizabilities and two-photon absorption properties fo r H2O in aqueous solution. The results are in close agreement with experime ntal measurements. (C) 2001 American Institute of Physics.