Compression behavior and structure of dense helium at high temperatures by molecular dynamics simulation

摘要

In this work, the isotherm and energy distribution at T=304 K of dense helium are studied by molecular dynamic (MD) simulations with exp-6 potential r~*=2.967 3 A (the position of the well min- imum) and ε/k_B=10.8 K (ε is the well-depth and k_B is the Boltzmann constant) given by Peter et al., and different values of stiffness parameter α. The optimized value of α=12.7 is deduced that can de- scribe the atomic interactions for dense helium satisfactorily. This optimized αin exp-6 potential is used to conduct MD simulations of two isotherms of dense helium at T=300 K and T=298 K. The calcula- tions are in good agreement with the experimental. We further employed this method to investigate the equation-of-state and structure of dense helium at higher temperatures and found that when the density remained 1.6 g/cm~3, the second peak of the radial distribution function would disappear in the tempera- ture range from 2 000 to 040 K, demonstrating that a solid-liquid transition or decrystallization had oc- curred.