The electronic, mechanical properties and in-plane negative Poisson’s ratio in novel pentagonal NiX2 (X = S, Se, Te) monolayers with strong anisotropy: A first-principles prediction

Abstract

Inspired by the groundbreaking discoveries of the transition metal dichalcogenides (TMDCs) materials, the structural stabilities, electronic and mechanical properties of the pentagonal NiX2 (X = S, Se, Te) monolayers were comprehensively investigated by the first-principles calculations. The NiS2, NiSe2, and NiTe2 monolayers are indirect semiconductors with bandgaps of ∼ 2.45, ∼ 2.31 and ∼ 1.88 eV by using the HSE06 functional. The elastic constant and phonon dispersion calculations show that the pentagonal NiX2 (X = S, Se, Te) monolayers are mechanically and dynamically stable without negative values in elastic constant and frequency. Ab initio molecular dynamics (AIMD) simulations demonstrate the thermal stabilities of pentagonal NiX2 (X = S, Se, Te) monolayers at 300 K and 600 K, as evidenced by the unnoticeable structural evolutions and slightly changes in total energy. The negative Poisson’s ratio (NPR) is discovered for the NiTe2 monolayer, and the authenticity is analyzed by the unique geometric structure, electronic properties and bonding characteristics, which further expands the potential application of the pentagonal NiTe2 monolayer with auxetic effect. Our present work would not only provide a fundamental understanding of structural stabilities, electronic and mechanical properties of the pentagonal NiX2 (X = S, Se, Te) monolayers, but also shed some light on the experimental investigation on the pentagonal NiTe2 monolayer with novel auxetic effect.