Thermodynamic behavior of the carbon schwarzite fcc (C-36)(2)

The thermodynamic behavior of the carbon schwarzite fcc (C-36)(2) has been studied by tight-binding molecular-dynamics simulations at constant tempera ture and pressure. The system is totally sp(2) bonded and it can be represe nted as a folded graphite sheet made by hexagonal and heptagonal rings. The structure has a density rho as low as rho = 1.05 gr/cm(3) at T = 300 K and a bulk modulus B, evaluated by measuring the volume variation upon applica tion of an external hydrostatic load, as large as B = 0.70 Mbar. At T simil ar to 4000 K, the structure unfolds via a topological transformation, which brings the value of the topological connectivity of the structure k(c) fro m k(c) = 19 (for a cell including four molecules) to k(c) = 3 (which is the value of a graphite sheet). The behavior of the structural, dynamical, and electronic-structure properties has been evaluated in the whole temperatur e range, below and above the temperature of the topological transition. [S0 163-1829(99)02148-7].