Structural Phase Trasformations via Ab-Initio Molecular Dynamics

TL;DR

This paper introduces a novel simulation method combining ab-initio molecular dynamics with variable cell shape techniques, enabling accurate quantum-mechanical modeling of solid-solid phase transitions under pressure and temperature changes.

Contribution

It presents the first simulation scheme that accurately models phase transformations with quantum forces and stress, improving predictive capabilities over empirical potentials.

Findings

Successfully simulated silicon metal-insulator transition under high pressure.

Demonstrated spontaneous phase transformations during simulations.

Validated the method's effectiveness for complex phase change phenomena.

Abstract

Available simulation methods, suitable to describe solid-solid phase transitions occurring upon increasing of presssure and/or temperature, are based on empirical interatomic potentials: this restriction reduces the predictive power, and thus the general usefulness of numeric simulations in this very relevant field. We present a new simulation scheme which allows, for the first time, the simulation of these phenomena with the correct quantum-mechanical description of interatomic forces and internal stress, along with the correct statistical mechanics of ionic degrees of freedom. The method is obtained by efficiently combining the Car-Parrinello method for ab- initio molecular dynamics with the Parrinello Rahman method to account for a variable cell shape. Within this scheme phase trasformations may spontaneously take place during the simulation with variation of external pressure and/or temperature. The validity of the method is demonstrated by simulating the metal-insulator transition in Silicon (from diamond structure to simple hexagonal structure) under high pressure.