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Comparative Analysis of the AM1-SM2 and PM3-SM3 Parametrized SCF Solvation Models for Free Energies in Aqueous Solution

Cramer, C. J.; Truhlar, D. G.
J. Comput.-Aid. Mol. Des. 1992, 6, 629.

Two new continuum solvation models have been presented recently, and in this paper they are explained and reviewed in detail with further examples. Solvation Model 2 (AM1-SM2) is based on the Austin Model 1 and Solvation Model 3 (PM3-SM3) on the Parameterized Model 3 semi-empirical Hamiltonian. In addition to the incorporation of phosphorus parameters, both of these new models address specific deficiencies in the original Solvation Model 1 (AM1-SM1), viz., 1) more accurate account is taken of the hydrophobic effect for hydrocarbons, 2) assignment of heavy-atom surface tensions is based on the presence or absence of bonded hydrogen atoms, and 3) consistent, improved treatments of specific hydration-shell water molecules are afforded. The new models offer considerably improved performance compared to AM1-SM1 for neutral molecules and essentially equivalent performance for ions. The solute charges within the Parameterized Model 3 Hamiltonian limit the utility of PM3-SM3 for compounds containing nitrogen and possibly phosphorus. For other systems both AM1-SM2 and PM3-SM3 give realistic results, but AM1-SM2 in general outperforms PM3-SM3. Key features of the models are discussed with respect to alternative approaches.

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