Cavity formation energies for diatomic and spherical solutes in a diatomichard body fluid

The chemical potentials of spherical and diatomic dumbbell particles dissol ved in a hard dumbbell fluid are determined using the Widom insertion Monte Carlo simulation method. Results obtained as a function of fluid density a nd solute-solvent size ratio are compared with previous simulation results and analytical hard body fluid expressions derived from bonded hard sphere (BHS), scaled particle theory (SPT), and corresponding hard sphere (CHS) eq uations of state. The BHS predictions best represent all the simulation res ults, while SPT predictions are comparably accurate except for small solute particles dissolved in high-density fluids, and CHS predictions are exact to first order in solute size and solvent density but somewhat less accurat e for large particles at high densities. Simulations of the excess reaction free energy for model dissociation and isomerization processes illustrate the subtle effects of solute shape on cavity formation energy for particles with identical molecular volumes. (C) 2000 American Institute of Physics. [S0021- 9606(00)50134-2].