An observable for vacancy characterization and diffusion in crystals

TL;DR

This paper introduces a quantum probe-based observable to locate and analyze vacancy dynamics in crystals, revealing new migration mechanisms and crystal reorientation phenomena through rare event simulations.

Contribution

It proposes a novel quantum probe density approach for vacancy characterization and identifies complex diffusion paths and mechanisms in crystal simulations.

Findings

Identified vacancy diffusion paths including long-range migration.

Discovered a collective vacancy migration mechanism involving multiple lattice sites.

Observed vacancy-induced crystal reorientation processes.

Abstract

To locate the position and characterize the dynamics of a vacancy in a crystal, we propose to represent it by the ground state density of a quantum probe quasi-particle for the Hamiltonian associated to the potential energy field generated by the atoms in the sample. In this description, the h^2/2mu coefficient of the kinetic energy term is a tunable parameter controlling the density localization in the regions of relevant minima of the potential energy field. Based on this description, we derive a set of collective variables that we use in rare event simulations to identify some of the vacancy diffusion paths in a 2D crystal. Our simulations reveal, in addition to the simple and expected nearest neighbor hopping path, a collective migration mechanism of the vacancy. This mechanism involves several lattice sites and produces a long range migration of the vacancy. Finally, we also observed a vacancy induced crystal reorientation process.