Comparative study of hybrid functionals applied to structural and electronic properties of semiconductors and insulators

TL;DR

This study systematically evaluates hybrid functionals in density functional theory for predicting structural and electronic properties of a diverse set of semiconductors and insulators, highlighting their strengths and limitations.

Contribution

It provides a comprehensive comparison of three hybrid functionals, assessing their accuracy for various materials and proposing an optimal approach for exchange energy treatment.

Findings

Hybrid functionals improve band gap predictions over GGA.

Long-range corrected hybrid functional accurately reproduces gaps in ionic and rare-gas solids.

HSE functional effectively describes covalent materials.

Abstract

We present a systematic study that clarifies validity and limitation of current hybrid functionals in density functional theory for structural and electronic properties of various semiconductors and insulators. The three hybrid functionals, PBE0 by Perdew, Ernzerhof, and Becke, HSE by Heyd, Sucseria, and Ernzerhof, and a long-range corrected (LC) functional, are implemented in a well-established plane-wave-basis-set scheme combined with norm-conserving pseudopotentials, thus enabling us to assess applicability of each functional on equal footing to the properties of the materials. The materials we have examined in this paper range from covalent to ionic materials as well as a rare-gas solid whose energy gaps determined by experiments are in the range of 0.6 eV - 14.2 eV: i.e., Ge, Si, BaTiO$_3$, $\beta$-GaN, diamond, MgO, NaCl, LiCl, Kr, and LiF. We find that the calculated bulk moduli by the hybrid functionals show better agreement with the experiments than the generalized gradient approximation (GGA) provides, whereas the calculated lattice constants by the hybrid functionals and GGA show comparable accuracy. The calculated energy band gaps and the valence-band widths for the ten prototype materials show substantial improvement using the hybrid functional compared with GGA. In particular, it is found that the band gaps of the ionic materials as well as the rare-gas solid are well reproduced by the LC-hybrid functional, whereas those of covalent materials are well described by the HSE functional. We also examine exchange effects due to short-range and long-range components of the Coulomb interaction and propose an optimum recipe to the short-range and long-range separation in treating the exchange energy.