Phase behavior of a hard sphere interaction site model of benzene

We present a study of the phase diagram for a hard sphere interaction site model of benzene using Monte Carlo computer simulation. The investigation c onsidered the fluid phase and three types of solid phases. Two of these are similar to experimentally determined structures of benzene and the third i s a structure which allows the system to reach a high packing density at hi gh pressure through a columnar-like arrangement of the molecules. Extensive calculations of the solid and fluid thermodynamic properties were made. Th e results show that, for the solid phase, the structure which enables the c losest packing of molecules is the most stable one. The solid structures si milar to those of benzene, while apparently mechanically stable, were found to be thermodynamically metastable for this purely hard core system. The s imulation results have been used to test the accuracy of the cell theory fo r the solid phase and an equation of state for the fluid phase due to Boubl ik, as well as phase diagram predictions obtained by using these approximat ions in combination. (C) 2000 American Institute of Physics. [S0021-9606(00 )51120-9].