CRITICAL-EVALUATION OF BENZENE ANALYTICAL NONBONDED FORCE-FIELDS - REPARAMETRIZATION OF THE MM3 POTENTIAL

An extensive characterization of six existing nonbonded analytical 12-site potential functions for benzene has been performed by computing various properties in all three phases. The computed properties include gas-phase benzene dimer energies and structures, benzene second-virial coefficients, liquid benzene densities and vaporization enthalpies, liquid benzene C-C and ring center-center radial correlation as well as orientational functions, crystal unit cell parameters, unit cell volumes, and heat of sublimation data for six aromatic compounds, The 12-6 potential of Jorgensen and Severance emerged as the best effective two-body potential in condensed phases, while the exp-6 potentials of Williams and Starr proved to be the most consistent in all three phases. Two new parameter sets have been obtained in the framework of the MM3 potential, and one of them represents significant improvement over the original MM3 parameters and is comparable in quality to the force field of Williams and Starr. An analysis of the 12-6 and exp-6 potential forms is given, and the question of whether point charges or point dipoles should be used and the relationships between properties in different phases have also been examined.