First-principles Study On Electronic Structure Regulation Of Graphene-based And Graphene-like Two-dimensional Materials

Regulating the electronic structure of materials is an important means to change the physical and chemical properties of materials and achieve specific functions.Due to the large surface area and atomic thickness of two-dimensional materials,their electronic structure is easily affected by external factors,so the regulation methods are very rich,and the effect of regulation is more significant.Revealing the response mechanism of the electronic structure of two-dimensional materials to different regulation means and determining the structure-activity relationship are the key scientific problems that need to be solved to improve the performance of such materials and realize their application.Based on first principles calculations,this paper investigates the regulation of electronic structure and physicochemical properties of several typical two-dimensional materials by pressure,surface modification,atomic doping,etc.The main research contents are as follows:Firstly,the evolution of the electronic structure of large-angle bilayer graphene under pressure was studied,and it was found that flat bands and van hove singularities would appear near the Fermi level of large-angle double-layer graphene under high pressure,and the possible superconductivity phenomenon was predicted.In addition,in this system,the larger the twist angle,the greater the pressure required to achieve a flat band,and the Fermi velocity gradually decreases as the pressure increases.This work points out that pressure,as a direct means to improve the coupling effect between layers,can regulate the electronic structure of double-layer graphene to a certain extent in synergy with the means of twist angle,which provides a new idea for the design of double-layer two-dimensional systems with strong coupling between layers under large twist angle.The above work did not take into account possible bonding between layers.The bonding between layers will significantly change the electronic structure of doublelayer graphene,such as band gap,frontier orbital,etc.Therefore,we further studied the mechanism of bilayer graphene forming interlayer σ bonds through surface modification.First,the stability of 30 diamane structures were explored.Based on the formation energy and phonon spectrum,12 stable structures were screened.The analysis of the electron localization function revealed that the stability of these structures is due to the strong bonds formed between layers.Among them,10 diamane structures are direct bandgap semiconductors,with a wide range of bandgap value,which is positively correlated with the electronegativity of groups.And p-type and ntype semiconductors can be realized by doping.Some structures have excellent electron mobility and optical absorption coefficient.This work provides a systematic understanding of the influence of surface modification on the interlayer bonding and electronic structure properties of double-layer graphene.We have discussed the formation of new σ bonds between graphene layers to regulate its electronic structure and properties.And at the same time,we studied the effect of the introduction of transition metal diatoms on electronic structure for existing σ bond break inside graphene and explore their application in electrocatalytic oxygen evolution reaction(OER).It is found that in the homonuclear diatomic model catalyst,only Ir2N6-C has a performance comparable to IrO2 under the single-site mechanism.The dual-site mechanism is less prone to occur due to the difficulty of oxygen desorption.Among the heteronuclear diatomic model catalysts,there are 30 model catalysts with comparable performance to IrO2 under the single-site mechanism,among which RhPtN6-C has excellent performance and an overpotential of 0.307 V.For the dual-site mechanism,there are 12 potential catalysts.among them,CuOsN6-C has the excellent performance with an overpotential of 0.138 V and relatively easy desorption of oxygen.Finally,the electronic structure origin of the model catalyst with excellent performance is explained by the D-band center model,hydrogen bond and bond length.This work provides a clear direction for the design of carbon-based diatomic OER catalysts with excellent performance.Finally,we extend the research object to the graphene-like structure VSSe,where non-metallic atom doping regulates its electronic structure,and explored its application in hydrogen evolution reaction(HER).The results show that the doping of S site or Se site by As atom and Si atom,as well as C atom and Ge atom doped into Se site,can greatly improve the HER activity in the VSSe plane.Electronic structure analysis showed that the strong interaction between the center of the pz orbital of the doped atom and the s orbital of the H atom resulted in a higher binding strength between the doped atom and the H atom,thereby activating the surface of VSSe.This work provides theoretical guidance for the experimental design of highly active twodimensional material HER catalysts.