Anomaly phase transition of silicon: a molecular dynamics study

Abstract

Silicon shows a very different trend while melting. Melting has remained a challenging subject from a long time. Especially, predicting the melting temperature of any solid substance still exists as a problem in many cases. This work is an attempt to study the mechanism of melting using classical molecular dynamics simulation, to define a set of parameters that could help us predict the behaviors of silicon at any temperature and also its phase transition mechanism. In order to understand the phenomenon, it is important to know the interaction potential governing the silicon system. Stillinger-Weber potential is a good model for Si atoms which takes into account two and three particle interactions. Melting of Silicon atoms is studied using Molecular Dynamics Simulation with the help of LAMMPS software. Heating and quenching processes is implemented on a system of Si atoms. Variations of various parameters like density, volume per atom, potential energy, Lindemann parameter, Non-Gaussian parameter, and coordination number with temperature has been studied. It has been found that melting in Si occurs in three stages. It involves pre-melting, melting and relaxation. Around 1450 k, the Gaussian parameter begins to jump. At this point, the potential energy and Lindemann parameter appear to be steady, indicating pre-melting. Lindemann index and potential energy (PE) take an upward inflection about 1600 k, and coordination number increases from 4 to 8, indicating diamond structural collapse. At temperatures above 1750 k, the non-Gaussian value drops abruptly, indicating that the solid is completely lost its crystallinity.