Theoretical models for the liquid-vapor and metal-nonmetal transitions of
alkali fluids are investigated. Mean-field models are considered first but
shown to be inadequate. An alternate approach is then studied in which each
statistical configuration of the material is treated as inhomogeneous, with the
energy of each ion being determined by its local environment. Nonadditive
interactions, due to valence electron delocalization, are a crucial feature of
the model. This alternate approach is implemented within a lattice-gas
approximation which takes into account the observed mode of expansion in the
materials of interest and which is able to treat the equilibrium density
fluctuations. We have carried out grand canonical Monte Carlo simulations, for
this model, which allow a unified, self-consistent, study of the structural,
thermodynamic, and electronic properties of alkali fluids. Applications to Cs,
Rb, K, and Na yield results in good agreement with observations.Comment: 13 pages, REVTEX, 10 ps figures available by e-mail
