Tianhai Zhu

Density functional solvation model based on CM2 atomic charges

We extend the SM5 solvation model for calculating solvation free energies of a variety of organic solutes in both aqueous and organic solvents so that it can be employed in conjunction with high-level electronic structure calculations. The extension is illustrated by presenting three implementations based on density-functional theory (DFT). The three implementations are called SM5.42R/BPW91/MIDI!6D, SM5.42R/BPW91/DZVP, and SM5.42R/BPW91/6-31G*. They have the following features: (1) They utilize gradient-corrected DFT with polarized double zeta basis sets to describe the electronic structure of a solute. The particular exchange-correlation functional adopted is Becke’s exchange with the Perdew–Wang 1991 correlation functional, usually called BPW91. The MIDI!6D, DZVP, and 6-31G* basis sets are used. (2) They employ fixed solute geometries in solvation calculations. The model is designed to predict solvation free energies based on any reasonably accurate gas-phase solute geometry. (3) The electric polarizati...

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.