INCORPORATION OF SOLVENT EFFECTS INTO DENSITY-FUNCTIONAL CALCULATIONSOF MOLECULAR-ENERGIES AND GEOMETRIES

In this paper, we present the implementation of the ''conductorlike sc reening model'' (COSMO) into the density functional program DMol. The electronic structure and geometry of the solute are described by a den sity functional method (DFT). The solute is placed into a cavity which has the shape of the solute molecule. Outside of the cavity, the solv ent is represented by a homogeneous dielectric medium. The electrostat ic interaction between solute and solvent is modeled through cavity su rface charges induced by the solvent. The COSMO theory, based on the s creening in conductors, allows for the direct determination of the sur face charges within the SCF procedure using only the electrostatic pot entials. This represents the major computational advantage over many o f other reaction held methods. Since the DMol/COSMO energy is fully va riational, accurate gradients with respect to the solute coordinates c an be calculated for the first time, without any restriction on the sh ape of the cavity. The solvation energies and optimized molecular stru ctures are calculated for several polar solutes. In addition, the tren ds in basicity of amines and the relative stabilities of molecular con formers are studied. Our results suggest that for neutral solutes, agr eement between calculated and experimental solvation energies of bette r than about 2 kcal/mol can be achieved. (C) 1995 American Institute o f Physics.