Comparative study of force fields for benzene

We have examined the ability of several atomic force fields of different forms to reproduce the structure and binding energy of benzene dimer as determined from quantum chemistry calculations, the experimental gasphase second virial coefficient of benzene, and thermodynamic and structural properties of liquid benzene. The force fields investigated were a united atom Lennard-Jones potential, a united atom Lennard-Jones potential with a point quadrupole, an anisotropic united atom model, and explicit (all) atom force fields with partial atomic charges and without partial atomic charges. These force fields which do not include electrostatic interactions predicted the planar sandwich structure (D-6h) to be the most stable dimer structure, in contrast to quantum chemistry calculations that indicate that the planar sandwich structure is a saddle point between stable parallel displaced (C-2h) geometries. Only the explicit atom + partial charge model predicted benzene dimer structures and energies that are in qualitative agreement with those from quantum chemistry calculations. A force field of this form for benzene is presented that accurately reproduces the gas-phase second virial coefficient of benzene and the thermodynamic properties of liquid benzene and does a reasonable job in reproducing the structure of liquid benzene and properties of benzene dimer as determined from quantum chemistry calculations.