Accurate prediction of band gaps and optical properties of HfO$_2$

TL;DR

This study uses advanced density functional theory methods to accurately predict the band gaps and optical properties of various hafnia polymorphs, including amorphous forms, aligning well with experimental data.

Contribution

It provides a comprehensive computational analysis of hafnia's optical properties across different phases using the Tran-Blaha potential and simulated annealing for amorphous structures, which is novel.

Findings

Predicted band gaps closely match experimental values.

Dielectric functions show a spectral shift explained by the RPA approximation.

Amorphous hafnia's properties are characterized alongside crystalline phases.

Abstract

We report on optical properties of various polymorphs of hafnia predicted within the framework of density functional theory. The full potential linearised augmented plane wave method was employed together with the Tran-Blaha modified Becke-Johnson potential for exchange and local density approximation for correlation. Unit cells of monoclinic, cubic, and tetragonal crystalline, and a simulated annealing-based model of amorphous hafnia were fully relaxed with respect to internal positions and lattice parameters. The thus obtained band gaps of 5.76 eV, 5.88 eV, 6.54 eV, and 5.5 eV for monoclinic, cubic, tetragonal, and amorphous hafnia, respectively, are in excellent agreement with available experimental data. Dielectric functions were calculated and a shift of spectral weights to higher energies with respect to experimental data was predicted. This was attributed to the random phase approximation used to calculate the dielectric function, rather than inaccuracies in the band structure.