| Abstract |
A comparative study, strictly by computer simulation, of the phase diagrams and sublimation enthalpies of model C-ngreater than or equal to60 fullerenes is presented. Gibbs ensemble and Gibbs-Duhem integration Monte Carlo simulations were carried out with the effective potentials of Girifalco. The triple-point properties were determined by a direct method recently proposed by us. It is based on the behavior of the Gibbs ensemble simulations at the lowest temperature limit, and it does not involve free-energy calculations or any other theoretical approach. According to the present results, the liquid phases of the studied fullerenes (C-60, C-70, C-76, and C-84) extend over similar to450 K. No sign of liquid supercooling was observed. The triple-point temperatures increase from C-60 to C-84. This and the simultaneous effect of molecular size cause a relative dislocation of the phase diagrams to higher critical temperatures and lower densities. The simulated enthalpies of sublimation increase from C-60 to C-84, and they are in very good agreement with the available experimental data. It is suggested that at least the predicted triple-point properties should approach those of real fullerenes. There is a strong correlation between the phase properties and the details of the interaction potentials, clearly reflected in the relative location of the phase diagram and enthalpy curves. On the whole, the simulated results are in good accordance with those recently reported by Abramo et al. (Abramo, M. C.; Caccamo, C.; Costa, D.; Pellicane, G. Europhys. Lett. 2001, 54, 468) from a combination of simulation, modified hypernetted chain (MHNC) theory, and a kind of corresponding states rule and confirm the consistency of the MHNC theoretical approach. The reduced properties, which also include the critical- and triple-point pressures as well as the sublimation enthalpies, confirm that some kind of corresponding states rule may be established for fullerenes. On the basis of that, the enthalpy of sublimation of C-96 is predicted. |
