A semiempirical quantum mechanical solvation model for solvation free energies in all alkane solvents

Using a linear fit of the solvent-ordering part of the microscopic surface tension to experimental macroscopic surface tensions, the Generalized Born/Surface Tension solvation model presented previously for n-hexadecane (called Solvation Model 4 or SM4), is extended to include all alkanes as solvents, including normal, branched, and cyclic alkanes. The general SM4 alkane model is applicable to any alkane solvent for which the macroscopic dielectric constant and surface tension are either known or estimable. It treats electrostatic effects, including polarization of the solute by a reaction field, in terms of a continuum dielectric model of the solvent, uses element-based surface tension terms to account for first-solvation-shell effects, and uses an element-independent surface tension to account for solvent-ordering effects that extend further into solution. The electrostatic terms are based on the recently developed Charge Model 1 (CM1) for computing atomic partial charges. This charge model allows the development of a single set of parameters which is applicable to both the AM1 and PM3 Hamiltonians and also to any other electronic structure method that provides reasonably accurate geometries and partial charges.