Zirconia and hafnia polymorphs -- ground state structural properties from diffusion Monte Carlo

TL;DR

This study employs diffusion Monte Carlo to accurately determine the structural properties, cohesive energies, and bulk moduli of zirconia and hafnia polymorphs, providing benchmarks and insights beyond traditional density functional theory calculations.

Contribution

The paper introduces highly accurate quantum Monte Carlo results for zirconia and hafnia polymorphs, offering benchmarks and clarifying discrepancies in previous DFT studies.

Findings

Quantum Monte Carlo yields precise structural parameters.

Results serve as benchmarks for DFT calculations.

Comparison with experimental data validates the approach.

Abstract

Zirconia (zirconium dioxide) and hafnia (hafnium dioxide) are binary oxides used in a range of applications. Because zirconium and hafnium are chemically equivalent, they have three similar polymorphs, and it is important to understand the properties and energetics of these polymorphs. However, while density functional theory calculations can get the correct energetic ordering, the energy differences between polymorphs depend very much on the specific density functional theory approach, as do other quantities such as lattice constants and bulk modulus. We have used highly accurate quantum Monte Carlo simulations to model the three zirconia and hafnia polymorphs. We compare our results for structural parameters, bulk modulus, and cohesive energy with results obtained from density functional theory calculations. We also discuss comparisons of our results with existing experimental data, in particular for structural parameters where extrapolation to zero temperature can be attempted. We hope our results of structural parameters as well as for cohesive energy and bulk modulus can serve as benchmarks for density-functional theory based calculations and as a guidance for future experiments.