Phase diagram of model C _{n ⩾ 70} fullerenes

Abstract

Recent studies have confirmed that model C60 has a stable liquid phase confined to a rather narrow temperature range; in this letter we determine the phase diagram of model C70 and show that also this fullerene possesses a liquid phase whose existence range is wider than that of C60. A "corresponding state" behaviour of C60 and C70, emerging from a description in terms of reduced quantities of both the interaction potential and the phase diagrams' parameters, is then extended to higher-order fullerenes. Critical-and triple-point densities and temperatures of C76, C84 and C92 are thereby predicted. The decreasing accuracy of such a representation of Cn>70 phase behaviour with increasing n is discussed in relation to the model potential features.

Free energy determination of phase coexistence in model C60: A comprehensive Monte Carlo study

“…8, the ∆s = 0 locus tends to overestimate the coexisting fluid density, thus affecting the location of the triple point in the phase diagram. We remark that a similar trend would emerge if the HansenVerlet prescription [18,23] for the height of the first peak of the structure factor were used [3]. In fact, the close correspondence between the two interpretations of the freezing transition in terms of structural indicators, has been recently pointed out in Ref.…”

“…A refinement of our preliminary report on the phase diagram of higher order fullerenes C n>60 [3] is also in progress. Finally, we plan to investigate the C 60 properties, as well as the phase behavior of systems constituted by doped fullerites, in the lowtemperature region of the solid phase.…”

“…It is actually known that a stable liquid-vapor coexistence still survives for the model envisaged here, albeit restricted to a few tens degree temperature range [11,12]. A tiny liquid pocket has been predicted also in the phase diagram of similar models of higher order fullerenes [3], although it is argued that even a modest reduction of the range of the forces might cause the disappearance of the liquid phase. The emerging borderline nature of the Girifalco model implies that the overall appearance of its phase diagram sensitively depends on the details of the interaction potential; in fact, the initial controversy around the existence of a stable liquid phase for this system [11,13] has been solved by taking into account on one side the full role of the attractive part of the interaction [14], and on the other, a conveniently large simulation sample [15].…”

“…The Girifalco model constitutes a prototype system in several respects; recent studies suggest that a similar "smeared out" spherical description can be attempted for C n>60 systems, although fullerene molecules with n > 60 can have a sensibly non-spherical shape; the cases n = 70, 76 and 84 have in particular been examined (see [3] and references therein). On the other hand, more refined calculations of the fullerene-fullerene interaction yield results very close to those predicted through the Girifalco model [4,5], and a similar representation has been used for the description of other hollow nanoparticles as carbon onions, or metal dichalcogenides (also termed inorganic fullerenes) as GaAs and CdSe [6].…”

Communication: Phase diagram of C36 by atomistic molecular dynamics and thermodynamic integration through coexistence regions

“…It turns out that the triple and critical point temperatures, T tr and T cr , are significantly lower, and much higher, respectively, of their counterparts for a rigid cage model of C 60 . 10,11,13,[15][16][17] We get thus evidence of a huge expansion of the stable liquid phase pocket of C 36 in comparison to that early found in C 60 . 10-12, 14, 16, 17 Moreover, the diffusion coefficient and the structural arrangement at the triple point density of C 36 , maintain liquid-like features over several hundreds degrees below T tr , by thus indicating a substantial extension of the "supercooled" liquid region.…”