Electronic structure calculations for rhenium carbonitride: An extended Hückel tight-binding study

Abstract

Effective theoretical models are needed to predict the physical properties of materials. Here we discuss the electronic structure of rhenium carbonitride (ReCN) in terms of tight-binding. The extended Hückel tight-binding (EHTB) formalism was employed to calculate the band structure, density of states (DOS) and investigate the chemical bonding properties as well as the crystal field splitting (CFS) of d orbitals in the Re atom. Two ReCN structures were studied, characterized by space groups P63mc and P3m1, respectively. The calculated energy bands and DOS depict semiconductor properties for both structures, seeing an indirect band-gap of 0.62 eV in P63mc (M - K) while a direct band-gap of 0.49 eV is seen in P3m1 at (H). Mulliken population and CFS analysis were done to gain insight into the filling of 5d orbitals in ReCN, crystallographical differences between the two crystal structures and their physical implications. The five-fold degenerate energy levels in both the P63mc and P3m1 structures are broken by a tetragonal crystal electric field. The P63mc structure undergoes Peierls distortion, resulting in a loss of symmetry. The EHTB method is an effective tool to approximate the physical and chemical properties of novel materials such as ReCN at a low computational cost and in terms of a simple quantum-mechanical framework, understood by the broader community. The EHTB model for ReCN will serve as a benchmark and starting point for future studies on the compound within similar contexts.