THE ENTROPY OF A NETWORK CRYSTAL, FLUID AND GLASS

The equation of state and entropy of the fluid, glass and crystalline phases of a tetravalent network model were studied by computer simulation. The super-cooled fluid is a glass below 0.58 of its melting temperature, at constant pressure. The entropy of the fluid is much larger than that of the crystal and there is no indication of an impending Kauzmann catastrophe. The statistical entropy of the network glass, obtained by computing its configuration integral, is 0.72 +/- 0.1 Nk lower than the thermal entropy, obtained by integrating the equation of state. That result implies that the number of topologically distinct four-connected networks is Omega(net) = exp (0.72 N), or about 10(67) for the simulated system of N = 216 molecules. The results are compared with a corresponding study of the hard sphere fluid and glass.