Calculation of solvation energies: the self-consistent multipole moment reaction field method

Abstract

The self-consistent multipole moment reaction field (SCMMRF) method is proposed as a simple alternative to the conventional self-consistent reaction field (SCRF) technique for the calculation of solvation energies within the confines of the dielectric continuum model. The SCMMRF method represents a straight forward generalization of the original Kirkwood method by the inclusion of the solute's polarizability. Formally, the SCMMRF method is identical to SCRF through second order in the reaction field in its present formulation, i.e., hyperpolarizability contributions are neglected. The SCMMRF method is particularly cost-effective when applied in conjunction with correlated wavefunctions, since it requires only multipole moments and their polarizabilities to be computed. Test calculations for the water and pyrimidine molecules and for several H₂O clusters demonstrate that the SCMMRF technique is a numerically reliable alternative to SCRF. Using a composite discrete-continuum approach, the hydration energy of water has been computed to be –8⋅9 kcal mol^-1, in acceptable agreement with the experimental value of –9⋅7 kcal mol^-1.