The role of Coulomb interaction on the electronic properties of monolayer NiX$_2$ (X = S, Se): A DFT+U+V study

TL;DR

This study investigates how Coulomb interactions influence the electronic properties of monolayer NiS2 and NiSe2, revealing their role in band gap formation and charge transfer insulating behavior through advanced DFT methods.

Contribution

It provides a systematic analysis of Coulomb interactions using DFT+U+V, highlighting their impact on electronic structure and phase characterization of monolayer Nickel dichalcogenides.

Findings

Coulomb interactions significantly affect band gap size.

Evidence of charge transfer insulating phase.

Comparison of functional methods clarifies electronic localization.

Abstract

The electronic structure of Nickel dichalcogenides, NiS$_2$ and NiSe$_2$, in monolayer form, is studied employing first-principles methods. We assess the importance of band ordering, covalency and Coulomb interactions in the ground state of these systems. Hybrid functional results are compared with standard functionals and also with Hubbard-corrected functionals to systematically address the role of electronic interactions and localization. We found that mean-field correlation realized by intersite Hubbard interactions are directly linked to the magnitude of the energy band gap, giving compelling evidence for the presence of a charge transfer insulating phase in these materials.