AUTHOR=Huynh Thi My Duyen , Nguyen Duy Khanh , Nguyen Thi Dieu Hien , Dien Vo Khuong , Pham Hai Duong , Lin Ming-Fa 

TITLE=Geometric and Electronic Properties of Monolayer HfX2 (X = S, Se, or Te): A First-Principles Calculation

JOURNAL=Frontiers in Materials

VOLUME=7

YEAR=2021

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2020.569756

DOI=10.3389/fmats.2020.569756

ISSN=2296-8016

ABSTRACT=<p>The essential properties of monolayer HfX<sub>2</sub> (X = S, Se, or Te) are fully explored by first-principles calculations. The optimal lattice symmetries, sublattice buckling, electronic energy spectra, and density of states are systematically investigated. Monolayer HfS<sub>2</sub>, HfSe<sub>2,</sub> and HfTe<sub>2,</sub> respectively, belong to middle-gap semiconductor, narrow-gap one and semimetal, with various energy dispersions. Moreover, the van Hove singularities (vHs) mainly arise from the band-edge states, and their special structures in the density of states strongly depend on their two or three-dimensional structures and the critical points in the energy-wave-vector space. The above-mentioned theoretical predictions are attributed to the multi-orbital hybridizations of [<inline-formula id="inf1"><mml:math id="minf1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>d</mml:mi><mml:mrow><mml:msup><mml:mi>x</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mo>−</mml:mo><mml:msup><mml:mi>y</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>, d<sub>xy</sub>, d<sub>yz</sub>, d<sub>zx</sub>, <inline-formula id="inf2"><mml:math id="minf2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>d</mml:mi><mml:mrow><mml:msup><mml:mi>z</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>]–[s, p<sub>x</sub>, p<sub>y</sub>, p<sub>z</sub>] in the Hf-X chemical bonds. The diversified physical phenomena clearly indicate a high potential for applications, as observed in MoS<sub>2</sub>-related emergent materials ions.</p>