Mesoscopic simulation of slow structural relaxation in fluid mercury near the metal-nonmetal transition

摘要

The Langevin diffusion equation approach is proposed for studying the metal-nonmetal (M-NM) transitions in expanded fluid mercury from a mesoscopic and dynamical viewpoint. In this theory, time evolutions of coarse-grained atomic densities are calculated in accordance with the free energy functionals that incorporate changes in the electronic states across the M-NM transitions. Because of the intrinsically discontinuous nature of the M-NM transitions, irregular mixing of high-density metallic domains and low-density nonmetallic domains is predicted in the M-NM transition range. Thermal fluctuations cause local transformation between metallic and nonmetallic domains. The timescale of structural relaxation involving such a local M-NM transition is remarkably slow, which is reflected in the strikingly slow time decay of the dynamical density correlation functions in the M-NM transition range. This result strongly supports the experimental evidence of slow structural relaxation found through anomalous sound wave attenuation. An increase in isothermal compressibilities and a modest enhancement of long-wavelength static structure factors are predicted across the transition. Discontinuous density jumps are smeared out by structural disorder, leading to a continuous M-NM transition in agreement with observations. [References: 47]