First-principles Study On Electronic Structure And Magnetic Properties Of 2D Metal Organic Frameworks

Material has important application in our production and life,but also promotes the development of human science and technology.Graphene has a two-dimensional planar structure.Since its discovery,its unique molecular structure and excellent physical properties make it a popular research topic in the field of electronic information,physics,materials science and other fields.Due to the revelation of graphene,a new type of two-dimensional carbon based materials have attracted more and more attention and become the focus of international academic research.As a new member of the family of two-dimensional materials,metal organic ligand self-assembled materials have great potential applications in the fields of energy and devices due to their unique properties,such as adjustable structure and function,large number of active sites and large specific surface area.In these areas,many researchers use a variety of physical or chemical means to actively explore new two-dimensional materials with special functions,especially the magnetic metal organic frameworks which have important applications in spintronics.However,relying solely on experimental exploration is bound to require high cost.First principles simulation based on quantum mechanics can design models which are meeting the requirements.The simulation characteristics and properties of the system are closer to the real situation.It also can greatly shorten the experimental period and reduce the cost,becoming an important foundation and core technology of computational materials science.Therefore,it has important applications in material design,synthesis,simulation calculation.In this paper,the first principles calculations based on density functional theory are used to study the electronic structure and magnetic properties of some two dimensional metal organic frameworks with coordination bonding configurations This thesis consists of four chapters.In chapter one,we first give a brief introduction to the magnetic properties of materials,especially the characteristics of ferromagnetism,anti-ferromagnetism and spin frustration.From the study of the magnetic properties to spintronics materials at nanometer scale,including half metallic ferromagnets and bipolar magnetic semiconductor materials.Secondly,we introduce the main methods and computing tools used in this study,including density functional theory and VASP software package.In the second chapter,we systematically studied the metal organic complexes TM-Cu3(C6S6)(TM=Cr,Mn,Fe,Co,Ni,Cu,Cu3(C6S6)=benzenehexathiol,Abbreviated as BHT)formed by a series of transition metals and organic ligands BHT containing S group.In this system,we mainly study the Co-BHT with ferromagnetic ground state and the Mn-BHT with spin frustrated ground state.The former is a metal material,and the latter can be controlled by carrier doping,which can realize a half metallic ferromagnetic ordering.Both of them have a very high temperature,which is of great significance to the application of two-dimensional materials.In the third chapter,we have studied the coordination configuration of alkali metal atoms(Na,K)and 2,3,6,7,10,11-HexabromotriphenyLene(C18H6Br6)on AU(111)substrates based on the experiment in the first half.Through theoretical analysis and calculation,we confirmed that the interaction between the C18H6Br6 molecule and the alkali metal on the gold substrate is a halide bond.R-Br as a Lewis base,the metal as a Lewis acid,the interaction between the two will form an angle of 90�-120�.We also analyzed the possible causes of the formation of the six coordination configuration of Na-C18Hf6Br6 and the four coordination configuration of K-C18H6Br6 complex on Au(111)substrate by calculating the formation energy.In the latter part of this paper,the K-C18H6R6(R=Cl,Br,I)systems were calculated by density functional theory.Among them,the k-C18Br6i6 and K-CisH6I6 are potential bipolar magnetic semiconductors,abbreviated as BMS,the K-C18H6Cl6 has a half metal structure.Finally,the stress and carrier doping were used to control the magnetic properties.In the fourth chapter,we mainly look for and design some two-dimensional metal organic configurations which may have the characteristics of half-metal.In the first part of this chapter,we propose a kind of novel two-dimensional material Mn3(C6X,N3H3)2 and Mn3(C6X6)(C6N6H6)(X=S,O)which are formed by transition metal Mn atom and organic ligand C12X6N6H6.Theoretical calculation found that they have high Curie temperature as well as the characteristics of half-metal.In the second part,we present a Mn3C12Br 12 structure containing Br and several MnxCySz structures with different coordination configuration.The results show that these structures have high Curie temperature.However,these structures are not stable after increasing temperature increasing.These studies provide support for the subsequent experimental and theoretical study of similar metal organic framework materials.In summary,using density functional theory we studied the geometrical structure,electronic structure and magnetic properties of different forms of two-dimensional self-assembly systems by the first principle calculation.These works not only reveal some novel properties of the two dimensional metal organic frameworks in the electronic and magnetic properties,expand our understanding to these systems,but also lay the foundation for further theoretical and experimental feasibility study.