SOLVENT AND VIBRATIONAL EFFECTS ON MOLECULAR ELECTRIC PROPERTIES - STATIC AND DYNAMIC POLARIZABILITY AND HYPERPOLARIZABILITIES OF UREA IN WATER

We present an application of a recently developed algorithm for the an alytical computation of the static and dynamic electric response funct ions: polarizability alpha, first and second hyperpolarizabilities bet a and gamma, for molecules in solution. The present method is formulat ed at the ab-initio level within the framework of a continuous model o f the solvent. In this procedure the solute molecule is embedded in a cavity of realistic shape, carefully modelled on its molecular surface , whereas solute-solvent interactions are described in terms of the re action field produced by a set of apparent surface charges (ASC) which represent the solvent polarization. The explicit computational model to which we refer for the calculation of the solvent effects is the po larized continuous model, PCM, developed in our laboratory. For the ca lculation of the dynamic polarizability alpha, and hyperpolarizabiliti es beta and gamma, this method allows the use of the frequency depende nt dielectric permittivity for the solvent, epsilon(omega), over the c omplete range of variability of the frequency omega of the applied osc illating field. As an application of this method, the polarizability a nd the hyperpolarizabilities of urea have been calculated in vacuo and in aqueous solution: taking into account that the solvent influence i mproves the agreement with experimental results. (C) 1998 Elsevier Sci ence B.V.