AN EQUATION OF STATE FOR FUSED HARD-SPHERE POLYATOMIC-MOLECULES

An equation of state for a fluid of fused hard sphere (FHS) molecules is developed based on an interpolation scheme which relates the free e nergy per particle to that of a fluid of tangent hard sphere (THS) mol ecules at the same packing fraction. Use of Wertheim's TPT1 (first ord er thermodynamic perturbation theory) equation for this latter quantit y yields an analytical expression for the compressibility factor for a ny shape of the FHS molecule. Predictions are in good agreement with t he simulation results for rigid homonuclear and heteronuclear diatomic s, linear and nonlinear triatomics, and tetrahedral pentatomics. For p urely repulsive models of n-alkane chains, it is found that the accura cy of the theory deteriorates with increasing chain length. The interp olation procedure is also generalized to the case of chemical associat ion.