Computational Study Of Magnetoelectric Coupling Effect And Flexoelectric Effect About α-In₂Se₃

Due to the excellent electrical,optical,thermal properties,as well as atomic layer thickness,two-dimensional materials can provide more efficient,smaller and lower power consumption solutions for the manufacturing of integrated circuits,which also can help improving the stability and reliability of chips.At present,the laboratory has successfully prepared a variety of two-dimensional materials,including:graphene,nitrite（h-Bn,AIN,etc.）,transition metal dichalcogenides（Mo S₂,WS₂,etc.）,ferroelectric materials（Cu In P₂S₆,Ge Se,In₂Se₃,etc.）and ferromagnetic materials（Cr₂Ge₂Te₆,Bi₂Te₃,1T-VSe₂,etc.）.In addition,two-dimensional materials can flexibly regulate their physical properties through appling external electric field,strain,chemical modification and heterojunction construction,which can greatly break through the limitations of traditional intrinsic materials in application due to their relatively simple functions.In this thesis,first-principles calculations are applied in the framework of density functional theory.On the basis ofα-In₂Se₃,the regulation of magnetoelectric coupling effect on electrical properties and magnetic properties of two-dimensional composite multiferros and the regulation of electrical properties such as energy band structure or charge distribution in two-dimensional materials are studied.It provides some theoretical guidance for the design of multifunctional materials and flexible devices.This thesis is divided into five chapters.The first chapter introduces the magnetoelectric coupling effect and flexoelectric effect of two-dimensional materials.The second chapter introduces the theoretical basis and research tools which are involved.Chapters 3 and 4 present the research of this thesis.Finally,in Chapter 5,the thesis summarizes the work done and focus on future research directions.The details of our work are as follow:In Chapter 3,we investigated the electrical and magnetic properties of VSe₂/In₂Se₃two-dimensional multiferroic heterojunctions,and investigated the effect of polarization on the energy band.We finally achieved a continuous variation of the heterojunction energy bands between type-I,II,and III alignment.In addition,we investigated the magnetic properties in VSe₂/In₂Se₃ heterojunctions,focusing on the modulation of the magnetic anisotropy energy of heterojunctions by reversing polarization directioon,and found that the magnetic moment and magnetic anisotropy energy of V atoms in heterojunctions varied to a larger extent when the polarization direction of In₂Se₃ is directed toward VSe₂ compared with that of monolayer VSe₂.In Chapter 4,we analyzed the flexoelectricity effect of monolayerα-In₂Se₃ by varying the strain gradient and polarization direction of the bending structure,finding that the difference in the electron cloud shapes of the s and p orbitals made the highest occupied molecular orbital（HOMO）and the lowest unoccupied molecular orbital（LUMO）responsed to stress differently.In addition to this,we also investigated the flexoelectricity effect of external electric field on the band gap of the monolayerα-In₂Se₃bending structure and found that the band gap decreased linearly with the increase of the strain gradient and external electric field.