A SYSTEMATIC AND FEASIBLE METHOD FOR COMPUTING NUCLEAR CONTRIBUTIONS TO ELECTRICAL-PROPERTIES OF POLYATOMIC-MOLECULES

An analytic method to evaluate nuclear contributions to electrical pro perties of polyatomic molecules is presented. Such contributions contr ol changes induced by an electric field on equilibrium geometry (nucle ar relaxation contribution) and vibrational motion (vibrational contri bution) of a molecular system. Expressions to compute the nuclear cont ributions have been derived from a power series expansion of the poten tial energy. These contributions to the electrical properties are give n in terms of energy derivatives with respect to normal coordinates, e lectric field intensity or both. Only one calculation of such derivati ves at the field-free equilibrium geometry is required. To show the us eful efficiency of the analytical evaluation of electrical properties (the so-called AEEP method), results for calculations on water and pyr idine at the SCF/TZ2P and the MP2/TZ2P levels of theory are reported. The results obtained are compared with previous theoretical calculatio ns and with experimental values. (C) 1997 American Institute of Physic s.