Molecular dynamics determination of liquid-vapor coexistence in molten alkali halides.

We show by extensive molecular dynamics simulations that accurate predictions of liquid-vapor coexistence in molten alkali halides can be achieved in terms of a rigid ion potential description in which temperature-dependent ionic diameters are employed. The new ionic sizes result from the fitting of the experimental isothermal compressibilities, a condition whose physical implications and consequences are illustrated. The same diameters also allow us to formulate confident predictions for the compressibilities of salts in cases where the experimental data are lacking. The extension of the present approach to molten alkali-halide mixtures and to other classes of molten salts is discussed.

Atomistic molecular dynamics simulations of model C(36) fullerite.

We report atomistic molecular dynamics investigations of a model C(36) fullerite in which the fullerene molecules are modeled as rigid cages over which the carbon atoms occupy fixed interaction sites, distributed in space according to the experimentally known atomic positions in the molecule. Carbon sites belonging to different molecules are assumed to interact via a 12-6 Lennard-Jones-type potential; the parameters of the latter are employed in the framework of a molecular dynamics fitting procedure, through which the ambient condition physical quantities characterizing the hcp structure of solid C(36) are eventually reproduced. We discuss applications of the adopted modelization to the C(36) phases in a temperature range spanning from 300 to 1500 K, and compare the obtained results to the available data for C(36) and other fullerenes, and to the predictions of the well known Girifalco central potential modelization of interactions in fullerenes, as applied to the C(36) case.

Phase and glass transitions in short-range central potential model systems: the case of C60.

Extensive molecular dynamics simulations show that a short-range central potential, suited to model C60, undergoes a high temperature transition to a glassy phase characterized by the positional disorder of the constituent particles. Crystallization, melting, and sublimation, which also take place during the simulation runs, are illustrated in detail. It turns out that vitrification and the mentioned phase transitions occur when the packing fraction of the system-defined in terms of an effective hard-core diameter-equals that of hard spheres at their own glass and melting transition, respectively. A close analogy also emerges between our findings and recent mode coupling theory calculations of structural arrest lines in a similar model of protein solutions. We argue that the conclusions of the present study might hold for a wide class of potentials currently employed to mimic interactions in complex fluids (some of which are of biological interest), suggesting how to achieve at least qualitative predictions of vitrification and crystallization in those systems.