Theoretical models for the alkali fluids

Unified self-consistent models representing the basic characteristics of the alkali fluids are reviewed. The self consistency consists of Monte Carlo simulations, in a classical lattice gas, to obtain atomic configurations which appear with a thermal probability e^F/k_BT, where the configurational free energy F is determined by that of a quantum mechanical electronic system with one valence electron per atom. The models allow calculation of the structural, thermodynamic, and electronic properties of the fluid. The results of such calculations have been compared with experimental data. The calculated properties which have been emphasized are the vapor–liquid coexistence curve and, at coexistence conditions, the electrical conductivity and the electronic paramagnetic susceptibility. The main conclusions which have been reached are the following. The asymmetric coexistence curves of these fluids arise from the effects of equilibrium density fluctuations which, due to the influence of delocalizable valence electrons, give rise to energies which are not pairwise additive. The nonmetal to metal transition in these fluids is predominantly due to the onset of percolation in the atomic structures driven by the electronic effects. Self consistency of atomic and electronic structures are crucial to the understanding of the properties of these fluids.