Self-consistent Reaction Field Model for Aqueous and Nonaqueous Solutions Based on Accurate Polarized Partial Charges

Marenich, A. V.; Olson, R. M.; Kelly, C. P.; Cramer, C. J.; Truhlar, D. G.

* J. Chem. Theory Comput.*
**2007**, *3*, 2011.

A new universal continuum solvation model (where "universal"
denotes applicable to all solvents), called SM8, is presented. It is an
implicit solvation model, also called a continuum solvation model, and it
improves on earlier SMx universal solvation models by including free
energies of solvation of ions in nonaqueous media in the parametrization.
SM8 is applicable to any charged or uncharged solute composed of H, C, N,
O, F, Si, P, S, Cl, and/or Br in any solvent or liquid medium for which a
few key descriptors are known, in particular dielectric constant,
refractive index, bulk surface tension, and acidity and basicity
parameters. It does not require the user to assign molecular-mechanics
types to an atom or group; all parameters are unique and continuous
functions of geometry. It may be used with any level of electronic
structure theory as long as accurate partial charges can be computed for
that level of theory; we recommend using it with self-consistently
polarized Charge Model 4 or other self-consistently polarized class IV
charges, in which case analytic gradients are available. The model
separates the observable solvation free energy into two components: the
long-range bulk electrostatic contribution arising from a self-consistent
reaction field treatment using the generalized Born approximation for
electrostatics is augmented by the non-electrostatic contribution arising
from short-range interactions between the solute and solvent molecules in
the first solvation shell. The cavities for the electrostatic calculation
are defined by superpositions of nuclear-centered spheres whose sizes are
determined by intrinsic atomic Coulomb radii. The radii used for aqueous
solution are the same as parametrized previously for the SM6 aqueous
solvation model, and the radii for nonaqueous solution are parametrized by
a training set of 220 bare ions and 21 clustered ions in acetonitrile,
methanol, and dimethyl sulfoxide. The non-electrostatic terms that are
proportional to the solvent-accessible surface areas of the atoms of the
solute have been parameterized using solvation free energies for the
training set of 2346 solvation free energies for 318 neutral solutes in 90
nonaqueous solvents and water and 143 transfer free energies for 93 neutral
solutes between water and 15 organic solvents. The model is tested with
three density functionals and with four basis sets: 6-31+G(d,p), 6-31+G(d),
6-31G(d), and MIDI!6D. The SM8 model achieves the mean unsigned errors of
0.5-0.8 kcal/mol in the solvation free energies of tested neutrals and
the mean unsigned errors of 2.2-7.0 kcal/mol for ions. The model
outperforms the earlier SM5.43R and SM7 universal solvation models as well
as the default Polarizable Continuum Model (PCM) implemented in *Gaussian
98/03*, the conductor-like PCM as implemented in *GAMESS*,
*Jaguar *'s continuum
model based on numerical solution of the Poisson equation, and the GCOSMO
model implemented in *NWChem*.

To request a copy of this article, send e-mail to the Research Reports Coordinator at the Minnesota Supercomputer Institute
(requests@msi.umn.edu). Please provide a mailing address and specify that
you would like **UMSI report 2007/244**.