Simulations of Nanocrystals Under Pressure: Combining Electronic Enthalpy and Linear-Scaling Density-Functional Theory

TL;DR

This paper introduces a linear-scaling density-functional theory implementation for simulating nanocrystals under pressure, enabling efficient geometry optimizations and molecular dynamics, with validated results on silicon nanocrystals.

Contribution

It presents a novel electronic enthalpy method integrated into a linear-scaling DFT code for finite systems under pressure, including calibration and validation procedures.

Findings

Good agreement with explicit solvent simulations.

Size-dependent pressure-induced structural transformations observed.

Identification of three amorphous structures in nanocrystals.

Abstract

We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [Phys. Rev. Lett., 94, 145501 (2005)], it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.