Study Of Manipulation On The Geometry And Electronic Structure Of Twisted Bilayer Graphene

The electronic structure of double-layer graphene is closely related to its different stacking and rotation modes,and it is easily regulated by external fields such as strain.However,so far,people have only extensively studied the physical properties of the rotating double-layer graphene with the two rotation centers of "atom" and "ring",and the rotating double-layer graphene with the "bond" as the rotation center has not been reported.In this article,we have summarized the Moore pattern law of double-layer graphene rotating a series of angles under the above three different rotation centers.On this basis,using the first-principles calculation method,the electronic structure of the corresponding structures under three different rotation centers under the application of vertical and horizontal strain is studied.We found that after applying a vertical strain,the electronic structure of the double-layer graphene under different rotation centers corresponds to its geometric structure.After applying horizontal strain,the electronic structure of the rotating double-layer graphene does not correspond to the geometric structure,but its energy band opens a larger band gap.There are five chapters in the thesis:The first chapter of the thesis is the introduction.First,the crystal and band structure of single-layer,double-layer and rotating double-layer graphene are introduced respectively.Then,the research situation of strain on the regulation of graphene band structure is introduced.Finally,the research content and significance of this article are explained.In Chapter 2,we briefly introduce the theoretical principle in computational work: Density Functional Theory(DFT).Then introduced the software package used in modeling and calculation: VASP.In Chapter 3,we specifically summarized the Moore of a series of rotation angles satisfying m=1,n=3,4,5,6...under three different rotation centers("atom","ring",and "bond")The pattern is regular.In Chapter 4,we use the first-principles calculation method to study the double-layer graphene rotating at a larger rotation angle.The structures corresponding to the three different rotation centers have similar band structures.However,when the vertical strain is applied,the energy bands of the three structures are quite different.The energy band of the corresponding structure with the "ring" as the center of rotation will open the band gap.As the strain increases,the band gap further increases,and the band gap reaches 55 me V at a strain of 20%.Next,we calculated the local average density of states and the differential charge density of the three structures after applying vertical strain.The peak of the low energy density of states and the region with the strongest interlayer interaction correspond to the local stacking of the three structures.On the.Finally,we summarized the changes in the band gap of the double-layer graphene under this rotation angle after horizontal strain is applied.In Chapter 5,we summarize the main research content and innovations of this article,and prospects for the follow-up research work.