<i>Ab initio</i>molecular dynamics study of the static, dynamic, and electronic properties of liquid Bi near melting using real-space pseudopotentials

Abstract

We perform a comprehensive study of the static, dynamic, and electronic properties of liquid Bi at $T=600\text{ }\text{K}$, $\ensuremath{\rho}=0.02876\text{ }{\text{\AA{}}}^{\ensuremath{-}3}$ by means of 124-atom ab initio molecular dynamics simulations based on PARSEC, a real-space implementation of pseudopotentials constructed within the density-functional theory. The predicted results are in good agreement with available experimental data, thus confirming the adequacy of this technique to achieve a reliable description of a nonsimple liquid metal such as liquid Bi, whose static structure has reminiscences of the rhombohedral structure of the crystal. The calculated intermediate scattering function $F(q,t)$ shows at low-$q$ values a strong diffusive component which imposes a slow decay of this function. The dynamic structure factor $S(q,\ensuremath{\omega})$ exhibits side peaks, indicative of collective density excitations, over a range of wave numbers up to $q\ensuremath{\approx}1.4\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$. Moreover, our simulations suggest an important ``positive dispersion effect'' for the density fluctuations of around 20%. We have also investigated the relaxation mechanisms for the density fluctuations by analyzing the different contributions to the second-order memory function of $F(q,t)$. Our results suggest that the thermal relaxation is the slow decaying channel, whereas the viscoelastic relaxation is the fast decaying channel. This behavior is just the opposite of that found in some liquid metals and may be attributed to the semimetal character of Bi.