Mesoscopic simulation of slow structural relaxation in fluid mercury near themetal–nonmetal transition

Abstract

The Langevin diffusion equation approach is proposed for studying the metal–nonmetal(M–NM) transitions in expanded fluid mercury from a mesoscopic and dynamicalviewpoint. In this theory, time evolutions of coarse-grained atomic densities are calculatedin accordance with the free energy functionals that incorporate changes in the electronicstates across the M–NM transitions. Because of the intrinsically discontinuous nature ofthe M–NM transitions, irregular mixing of high-density metallic domains andlow-density nonmetallic domains is predicted in the M–NM transition range. Thermalfluctuations cause local transformation between metallic and nonmetallic domains.The timescale of structural relaxation involving such a local M–NM transition isremarkably slow, which is reflected in the strikingly slow time decay of the dynamicaldensity correlation functions in the M–NM transition range. This result stronglysupports the experimental evidence of slow structural relaxation found throughanomalous sound wave attenuation. An increase in isothermal compressibilities and amodest enhancement of long-wavelength static structure factors are predictedacross the transition. Discontinuous density jumps are smeared out by structuraldisorder, leading to a continuous M–NM transition in agreement with observations.