Improved Methods for Semiempirical Solvation Models

Liotard, D. A.; Hawkins, G. D.; Lynch, G. C.; Cramer, C. J.; Truhlar, D. G.

*J. Comput. Chem.*
**1995**, *16*, 422.

We present improved algorithms for the SM*x* (*x* = 1,
1a, 2, 3) solvation models presented previously [see the overview in
C. J. Cramer and D. G. Truhlar, *J. Comput.-Aided Mol. Design*,
**6**, 629 (1992)]. These models estimate the free energy of
solvation by augmenting a semiempirical Hartree-Fock calculation on
the solute with the generalized Born (GB) model for electric
polarization of the solvent and a surface tension term based on
solvent-accessible surface area. This paper presents three
improvements in the algorithms used to carry out such calculations,
namely (i) an analytical accessible surface area algorithm, (ii) a
more efficient radial integration scheme for the dielectric screening
computation in the GB model, and (iii) a damping algorithm for
updating the GB contribution to the Fock update during the iterations
to achieve a self-consistent field. Improvements (i) and (ii)
decrease the computer time, and improvement (iii) leads to more stable
convergence. Improvement (ii) removes a small systematic numerical
error that was explicitly absorbed into the parameterization in the
SM*x* models. Therefore we have adjusted the parameters for one
of the previous models to yield essentially identical performance as
was obtained originally while simultaneously taking advantage of
improvement (ii). The resulting model is called SM2.1. The fact that
we obtain similar results after removing the systematic quadrature
bias attests to the robustness of the original parameterization.

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