Effects of electron correlation on thermodynamic properties of expanded alkali fluids

On the basis of the lattice-gas Hubbard model, which is the extension of the original Hubbard model for a crystal to the lattice-gas system, the thermodynamic properties of expanded alkali fluids are investigated to clarify how electron correlation, which causes the metal-non-metal transition in these fluids, influences their thermodynamic behaviours near the critical point of the liquid-vapour (LV) transition, and especially at the transition itself. The thermodynamic potential is calculated in a self-consistent combination of approximations: the molecular-field approximation for treating random atomic arrangements and the single-site coherent-potential approximation due to Yonezawa and Watabe for dealing with electron correlation. The results calculated for the equation of state are analysed in detail and it is pointed out that the peculiar behaviour of the LV transition observed for fluid caesium could be caused by the effects of electron correlation.