Nucleating a Different Coordination in a Crystal under Pressure: A Study of the B1-B2 Transition in NaCl by Metadynamics

TL;DR

This paper introduces a novel NPT metadynamics simulation method using coordination number and volume to study pressure-induced phase transitions, successfully applied to NaCl's B1-B2 transformation, revealing nucleation mechanisms and size-dependent transition pathways.

Contribution

The study develops a new simulation scheme for pressure-induced structural transitions, enabling analysis of nucleation and growth mechanisms in large systems beyond collective models.

Findings

Observed nucleation and growth in NaCl B1-B2 transition.

Identified crossover from Buerger-like to Watanabe-Tolédano mechanisms.

Demonstrated applicability to large systems with realistic conditions.

Abstract

Here we propose an NPT metadynamics simulation scheme for pressure-induced structural phase transitions, using coordination number and volume as collective variables, and apply it to the reconstructive structural transformation $B1$-$B2$ in NaCl. By studying systems with size up to 64 000 atoms we reach a regime beyond collective mechanism and observe transformations proceeding via nucleation and growth. We also reveal the crossover of the transition mechanism from Buerger-like for smaller systems to Watanabe-Tol\'{e}dano for larger ones. The scheme is likely to be applicable to a broader class of pressure-induced structural transitions, allowing study of complex nucleation effects and bringing simulations closer to realistic conditions.