Analytical energy gradients of a self-consistent reaction-field solvation model based on CM2 atomic charges

Analytical energy gradients have been derived for an SM5-type solvation model based on Hartree–Fock self-consistent reaction-field theory and CM2 atomic charges. The method is combined with an analytic treatment of the first derivatives of nonelectrostatic first-solvation-shell contributions to the free energy and implemented in the General Atomic and Molecular Electronic Structure System (GAMESS). The resulting equations allow one to use accurate class IV charges to calculate equilibrium geometries of solutes in liquid-phase solutions. The algorithm is illustrated by calculations of optimized geometries and solvation free energies for water, methanol, dimethyl disulfide, and 9-methyladenine in water and 1-octanol.