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

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.