Absolute Solvation Free Energies from Quasi-Chemical Theory

David Rogers, University of Cincinnati

Quasi-chemical theory, as introduced by Lawrence Pratt and colleagues, provides an exact separation of the excess chemical potential into local, chemical interactions and long-ranged packing and dispersion and/or electrostatic contributions due to the solution environment. The local contribution can be obtained from ab-initio, quantum mechanical calculations or estimated from classical dynamics simulations. The packing contribution is the excess chemical potential of a hard-core solute and can be estimated from simulations of pure water using a 2-moment Gaussian “information theory” model. A general method is presented for obtaining upper and lower bounds for the long-ranged contribution in this formalism. This separation is applied to estimate the solvation free energies of several small molecule solutes. The advantages and limitations of the method are discussed.

Abstract Author(s): David M. Rogers and Thomas L. Beck