Ab initiomolecular-dynamics simulations of the structural properties of liquidIn20Sn80in the temperature range798–1193K

Abstract

Ab initio molecular dynamics simulations on a liquid ${\mathrm{In}}_{20}{\mathrm{Sn}}_{80}$ alloy have been carried out at six different temperatures from $798\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1193\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We have studied the temperature-dependent structure properties, including binding energy, volume, pair correlation function, coordination number, structure factor, and bond-angle distribution function. The dynamical and electronic properties have also been studied. The calculated pair correlation function is in agreement with experimental data. A shoulder was reproduced in the high wave number side of the first peak in the calculated structure factor and the angle distribution function shows two peaks located at about 53\ifmmode^\circ\else\textdegree\fi{} and 102\ifmmode^\circ\else\textdegree\fi{}, implying the existence of the residual directional bonds of Sn atoms in a liquid ${\mathrm{In}}_{20}{\mathrm{Sn}}_{80}$ alloy. The coordination number of a Sn atom and the first-peak height of the calculated structure factor decrease more sharply in a low-temperature region from $798\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}986\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ than that in a high-temperature region from $986\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1193\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, so there is a noticeable bend at around $986\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the curves of both coordination number versus temperature, and peak height versus temperature. In the high temperature region, the most prevalent atomic bonded pairs are the 1311 type, whereas in the low temperature region, the most prevalent atomic bonded pairs are the 1551 type. In the middle temperature region $(929--986\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, with decreasing temperature, there seems to exist a steplike increase for 1551-, 1541-, 1441-, and 1431-type pairs and a steplike decrease for 1201-, 1311-, 1321-, and 1422-type pairs. However, the analysis based on the two-state model and the additional calculation at $963\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ show that the change in local atomic structures is continuous, indicating that the abnormal structure change that happened in liquid ${\mathrm{In}}_{20}{\mathrm{Sn}}_{80}$ is not of first order.