Theoretical Study Of Structure Prediction And Related Electron Properties For Several Two-dimensional Nanomaterials

In 2004,the exfoliation of graphite,namely graphene,was successfully fabricated by Geim and Novoselov.Since then,the research of two-dimensional（2D）materials has rapidly risen to be one of the hot spots of condensed matter physics due to their festinating electronic,mechanical,optical or magenetic properties and more and more 2D materials have been successfully discoveried or fabricated.On the premise of full investigation,we study severial 2D materials through the first-principle calculations.The research topic mainly includes the following works:Based on the CALYPSO,we successfully predicted a new 2D material,namely BeC monolayer.As we know,the stable 2D materials with planar hypercorrdinate motifs are extremely rare due to the difficulty in stabilizing the planar hypercoordinate configurations in extended systems.However,we predict a novel BeC monolayer featuring planar tetracoordinate carbon.In the BeC monolayer,each C atom is perfectly planar tetracoordinate and all atoms are in the same plane.In addition,BeC is an indirect semiconductor with a band gap of 1.01 eV and possesses exceptional high carrier mobilities(¹0⁴cm²V^-1s^-1),rendering it suitable for applications in electronics and photoelectronics.Besides the BeC monolayer,we also predicted a new MgN₂ monolayer.The cohesive energy,phonon-spectrum and mechanical stability criteria confirm the stability of monolayer MgN₂.In addition,according to the first principle calculation,we also find that the MgN₂ is an indirect semiconductor with a band gap of 2.06 eV,which is potential for applications in electronics and photoelectronics.Last,we study the adsorption behaviors of gas molecules on the Cu₂Si monolayer by first-principles calculations.Based on first-principles calculations,we investigate the adsorption of various gas molecules（O₂,NO,NO₂,NH₃,N₂,CO,CH₄ and CO₂）on the 2D Cu-Si extended system（Cu₂Si）.The changes in magnetization upon the gas adsorption may be detected sensitively and safely,suggesting the Cu ₂ Si monolayer is potential for gas sensing.