Onsite and intersite electronic correlations in the Hubbard model for halide perovskites

TL;DR

This study demonstrates that self-consistent DFT+U+V calculations significantly improve the accuracy of electronic structure predictions for halide perovskites, capturing complex correlations more efficiently than traditional methods.

Contribution

It introduces a self-consistent approach to determine Hubbard U and V parameters, enhancing band gap predictions and understanding of local charge states in halide perovskites.

Findings

Hubbard corrections improve band gap accuracy across different HP types.

Self-consistent Hubbard U indicates true local charge states.

Intersite Hubbard V is essential for capturing hybridization in distorted HPs.

Abstract

Halide perovskites (HPs) are widely viewed as promising photovoltaic and light-emitting materials for their suitable band gaps in the visible spectrum. Density functional theory (DFT) calculations employing (semi)local exchange-correlation functionals usually underestimate the band gaps for these systems. Accurate descriptions of the electronic structures of HPs often demand higher-order levels of theory such as the Heyd-Scuseria-Ernzerhof (HSE) hybrid density functional and GW approximations that are much more computationally expensive than standard DFT. Here, we investigate three representative types of HPs, ABX3 halide perovskites, vacancy-ordered double perovskites (VODPs), and bond disproportionated halide perovskites (BDHPs), using DFT+U+V with onsite U and intersite V Hubbard parameters computed self-consistently without a priori assumption. The inclusion of Hubbard corrections improves the band gap prediction accuracy for all three types of HPs to a similar level of advanced methods. Moreover, the self-consistent Hubbard U is a meaningful indicator of the true local charge state of multivalence metal atoms in HPs. The inclusion of the intersite Hubbard V is crucial to properly capture the hybridization between valence electrons on neighboring atoms in BDHPs that have breathing-mode distortions of halide octahedra. In particular, the simultaneous convergence of both Hubbard parameters and crystal geometry enables a band gap prediction accuracy superior to HSE for BDHPs but at a fraction of the cost. Our work highlights the importance of using self-consistent Huabbard parameters when dealing with HPs that often possess intricate competitions between onsite localization and intersite hybridization.