نرگس مهدی پور

A many-body dissipative dynamics simulation approach is presented for inclusion of many-body interactions in fluid cesium. Employing this many-body potential, simulations are done, in the grand canonical ensemble, to calculate the vapor?liquid equilibria over a wide range of temperatures (from the melting temperature to the critical temperature). The calculated coexisting liquid and vapor densities and the vapor pressures are in close agreement with experiment. The metal-nonmetal transition is examined in terms of cluster formation in low density cesium with increasing pressure. Our analysis of cluster formation along the critical isotherm shows that at pressures noticeably higher than the critical pressure very large spherical clusters are formed in the simulation box. The cluster sizes decrease with decreasing pressure to the critical pressure. At the critical pressure, only small clusters are seen in the simulation box. The cluster structures also change noticeably as the metal?nonmetal transition approaches. In the metallic state, high-density, spherical clusters are formed. Decreasing the pressure to the critical pressure causes rearrangement in the structure of spherical clusters to ellipsoidal (lower density) clusters. In the nonmetallic region, the clusters are very diffuse (low density) and do not have a well-defined structure. Adopting the fraction of cesium atoms involved in clusters larger than a threshold size as the fraction contributing to electrical conductivity, our simulation results well predict a sudden decrease in the electrical conductivity in close agreement with experimental observations.