A unique pentagonal network structure of the NiS2 monolayer with high stability and a tunable bandgap

Abstract

Two dimensional atomic crystals with pentagonal building blocks have attracted extensive interest in recent years for their fundamental significance and potential applications in nanoscale devices. Here, with the help of ab initio calculations based on density functional theory, we report a unique pentagonal structured NiS₂ monolayer in P2₁m symmetry, named P-NiS₂. Its dynamic stability has been confirmed by phonon mode analysis. Molecular dynamics simulations and total-energy calculations show that this new P-NiS₂ has robust thermal stability and energetically more stable than all other reported NiS₂ monolayer structures. Electronic band structure calculations show that it is a semiconductor with an indirect band gap of 1.94 eV. Furthermore, we find that small strain triggers a transition from the indirect to direct band gap for this P-NiS₂, suggesting its great potential for applications based on strain-engineering techniques.