VBSM: A Solvation Model Based on Valence Bond Theory

Su, P.; Wu, W.; Kelly, C. P.; Cramer, C. J.; Truhlar, D. G.

* J. Phys. Chem. A*
**2008**, *112*, 12761.

A new solvation model, called VBSM, is presented. The model combines
valence bond (VB) theory with parameters determined for the SM6 solvation
model (SM6, C. P. Kelly, C. J. Cramer, and D. G. Truhlar, *J. Chem. Theory
Comp.* **2005**, *1*, 1133-1152). VBSM, like SM6, is based on
the generalized Born (GB) approximation for bulk electrostatics and atomic
surface tensions to account for cavitation, dispersion, and solvent
structure (CDS). The solvation free energy of VBSM includes (i) a
self-consistent polarization term obtained by using VB atomic charges in a
GB reaction field with a VB self-consistent field procedure that minimizes
the total energy of the system with respect to the valence bond orbitals
and (ii) a geometry-dependent CDS term to account for deviations from
bulk-electrostatic solvation. Test calculations for a few systems show that
the liquid-phase partial atomic charges obtained by VBSM are in good
agreement with liquid-phase charges obtained by charge model CM4 (C. P.
Kelly, C. J. Cramer, and D. G. Truhlar, *J. Chem. Theor. Comp.*
**2005**, *1*, 1133-1152). Free energies of solvation are
calculated for two prototype test cases, namely for the degenerate
S_{N}2 reaction of Cl^{-} with CH_{3}Cl in water
and for a Menshutkin reaction in water. These calculations show that the
VBSM method provides a practical alternative to single-configuration
self-consistent field theory for solvent effects in molecules and chemical
reactions.

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