cQ& . -- Kl # JOURNAL OF NON-CRYSTALLINE SOLIDS ELSEVIER Journalof Non-Crystalline Solids 205-207 (1996) 251-255 Calculated structure, phase coexistence, and electrical conductivity of the alkali fluids E. Chac6n a, J.P. Hernandez bs * , P. Tarazona ’ a CSIC and Fisica Fundamental UNED, Ap. 60141, E-28028 Madrid, Spain b Physics and Astrollomy UNC, Chapel Hill, NC 27599-3255, USA ’ Fisica de la Materia Condensada (C-XII) UAM, E-28049 Madrid? Spain Abstract Energy estimates, which depend on the local coordination of each ion, are usedin grand canonical Monte Carlo simulations of a lattice-gasmodel for the alkali fluids. The non-additive interactions dueto valence electron delocalization are a crucial feature of the model. Theseself-consistent calculations treat the structural,thermodynamic, and electronic aspects of these fluids in a unified manner andobtain a liquid-vapor coexistence curve and an electrical conductivity, for the alkali family, in goodagreement with experimental observations. The authors’ previous work is improvedand extended. 1. Introduction Experimental studies of metal-atom fluids which have reached the high temperatures and pressures characteristic of their liquid-vapor critical points have become precise and reliable and span thermo- dynamic and electrical measurements under the same conditions. Data is available for those materials with the lowest critical temperatures: Hg (1751 K), Cs (1924 K), and Rb (2017 K) [l], with data on K (2178 K) now being available [2]; detailed data near the critical points of cesium and rubidium have been published [3]. The electronic and thermodynamic properties of such fluids are intimately related and have posed a long-standing challenge to theory. * Corresponding author. Tel.: + l-919-9627216; fax: -I- l-919- 9620480; e-mail: hemandz@physics.unc.edu. Theoretical understanding of the structural, ther- modynamic, and electronic properties of metal-atom fluids poses a considerable scientific challenge. Its various aspects are coupled since it is the electrons which determine interatomic interactions and thus the structure and thermodynamic data. The ionic structure, in turn, determines the electronic proper- ties 141. In the study of metal-atom fluids it is difficult to impose a structure, since it is so inti- mately related to the localization and delocalization of the valence electrons. The microscopic theory required for thesematerials should explain the essen- tial interdependence of thermodynamic, structural, and electronic properties. General arguments based on electron correlation effects (Hubbard model) and/or disorder induced localization (Anderson model) [5] are useful to study the metal-non-metal transition in systems with frozen ionic structure, but we are not aware of attempts, using such techniques, to comprehensively treat the properties of metal-atom 0022-3093/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved, PZi SOO22-3093(96)00233-5