Evaluation of collective transport properties of ionic melts from molecular dynamics simulations

Abstract

Molecular dynamics simulations of beryllium fluoride (BeF₂) have been carried out in the canonical (NVT) ensemble using a rigid-ion potential model. The Green-Kubo formalism has been applied to compute viscosities and ionic conductivities of BeF₂ melt. The computational parameters critical for reliably estimating these collective transport properties are shown to differ significantly for viscosity and ionic conductivity. In addition to the equilibrium values of these transport properties, structural relaxation times as well as high-frequency IR-active modes are computed from the pressure and charge-flux auto correlation functions (ACFs) respectively. It is shown that a network-forming ionic melt, such as BeF₂, will display persistent oscillatory behaviour of the integral of the charge-flux ACF. By suitable Fourier transformation, one can show that these persistent oscillations correspond to high-frequency, infra-red active vibrations associated with local modes of the network.