A DFT+$U$+$V$ study of pristine and oxygen-deficient HfO$_2$ with self-consistent Hubbard parameters

TL;DR

This study employs self-consistent DFT + U + V calculations to analyze pristine and oxygen-deficient HfO$_2$, demonstrating comparable accuracy to hybrid functionals in predicting stability and electronic properties while offering computational efficiency.

Contribution

It introduces a cost-effective method using self-consistent Hubbard parameters to accurately model HfO$_2$'s electronic structure and defect formation energies.

Findings

Self-consistent DFT + U + V matches hybrid functional accuracy.

Hubbard parameters indicate bond strengths and electronic structure.

Efficient prediction of oxygen vacancy formation energies.

Abstract

HfO$_2$-based ferroelectrics have emerged as promising materials for advanced nanoelectronics, with their robust polarization and silicon compatibility making them ideal for high-density, non-volatile memory applications. Oxygen vacancies, particularly in positively charged states, are suggested to profoundly impact the polymorphism kinetics and phase stability of hafnia, thereby affecting its ferroelectric behavior. The electronic structures of pristine and oxygen-deficient hafnia polymorph have been extensively studied using density functional theory, primarily employing (semi-)local exchange-correlation functionals. However, these methods often underestimate band gaps and may not accurately capture the localized nature of $d$-electrons. In this work, we investigate hafnia in various phases using DFT + $U$ + $V$, with onsite $U$ and intersite $V$ Hubbard parameters computed self-consistently via the pseudohybrid Hubbard density functional, ACBN0, and its extended version eACBN0. We find that the self-consistent DFT + $U$ method provides comparable accuracy to the computationally more expensive Heyd-Scuseria-Ernzerhof (HSE) hybrid density functional in predicting relative thermodynamic stability, band gaps, and density of states. Furthermore, it is a cost-effective approach for estimating the formation energies of oxygen vacancies. Additionally, we demonstrate that environmentally dependent Hubbard parameters serve as useful indicators for analyzing bond strengths and electronic structures in real space.