The Simulation And Performance Study Of Carbon And Silicon Low Dimensional Stable Structure

Graphyne material is one of research hotspots recently.In recent years,with continuous improvement of theoretical and experimental method,the graphyne nanomaterials research has made great progress.Much work about preparation,characterization,doping and related mechanical properties of graphyne has been reported in recent years.Compared with graphene,graphyne is more suitable for being applied as field-effect transistor.In addition,the bandgap of graphyne is closed to the silicon,it promote the conversion of the light-energy and can be used in optical device.In recent years,despite the research about graphyne have been done a lot,now we are still far from complete understanding of these intriguing materials.Meanwhile,a lot of challenges for the future remain in some directions.As we all know,the experiments considerably lag behind the theory,the most urgent task is to find novel preparation techniques.Besides,the search for new analogues based on graphyne through theoretical calculations seems very desirable.It will lead to the expansion of the family of the graphyne and discover more unexpected properties.In this paper,an efficient molecular dynamics scheme based on a semi-empirical Hamiltonian combined with First Principles theoretical calculations were adopted as calculation method.We will use it to do relaxation about many forms of silicon-graphyne and search the stable structure.In the second chapter,we will detail the theoretical basis of SCED-LCAO method.Then we briefly introduce the research method with the focus on the framework of density function theory,their developments and exchange correlation.In the third chapter,a study to shed light on the existence of Silicon-graphdiyne together with their stability,structural and other properties,has been carried out using an efficient semi-empirical Hamiltonian scheme based on quantum mechanics.Its most stable structure is a single planar structure with a lattice constant of 12.251?.The system occurs structural phase transition at 1520 K.When the temperature is above 1520 K,the basic structure will be destroyed.When the temperature is below 1520 K,the system can restore its initial structure.It is found that sp hybridization exist between Si and C atoms in this conjugated structure.The study of pair distribution function shows that sp bond length is about 1.58 ?.The sp hybridization gradually transformed into other forms of hybridization at high temperature.Our calculation indicates that delocalized π-bonds exist in this system and all the lengths of Si-C bonds tend to be more uniform.The energy gap is 1.416 eV.LUMO and HOMO energy level,are 0.386 eV and-1.03 eV respectively.It reveals that the Silicongraphdiyne should be n-type material.In the fourth chapter,We have demonstrated that a stable silicon-graphyne structure can be obtained by relaxing an initial configuration of graphyne which doped with silicon atoms in the special position.We explained how to use the method of design for different initial structure of silicon-graphyne,and then do simulation of the stability of the this structure.Our results show that the SiC graphyne and Si1C9 graphyne are stabilized to a flat sheet structure,while,the most stable Si2C8 graphyne is a slightly buckled structure with the buckling of 0.05?.The most interesting finding is that the sp hybridization not only exists between C atoms,but also exists between Si and C atoms,indicating the flexibility of Si-C bonding nature in the SiC systems.Another significant finding is that the electronic structures of the SimCn graphyne are sensitive to the location of the Si atoms(i.e.,the stoichiometry of C and Si elements).In Si2C8 structure,all the six corner positions are occupied by the Si atoms,and a tiny gap appears at the M point.While in the SiC and the Si1C9 graphynes,only part of the corner positions are occupied by carbon atoms and an obvious band gap opens in these two systems.These two systems behave as a semiconductor with the energy gap of 0.955 eV for the SiC graphyne and 0.689 eV for the Si1C9 graphyne,respectively.The study on temperature dependence reveals that the obtained structures are rather stable below 700 K for the SiC graphyne,800 K for the Si1C9 graphyne,and 1000 K for the Si2C8 graphyne,respectively.They will be destroyed only when the temperature reaches 2350 K(for SiC graphyne),or 2600 K(for Si1C9 graphyne),or 3300 K(for Si2C8 graphyne).In the fifth chapter,the structural stability,the strain-induced electronic properties of the α-Si1C7-graphyne monolayers have been systematically studied by first-principles calculations.Compared with α-graphyne,the Dirac-cone electronic structure disappeared due to the substitution of C atoms by Si atoms and a direct-band gap of 0.83 e V was found.The electronic properties of α-Si1C7-graphyne under the symmetrical biaxial and asymmetrical uniaxial strains is investigated.The calculated results reveal that the band gap decreased linearly under the biaxial strain,while the asymmetrical uniaxial strains along armchair direction could make the gap decrease in a parabolic trend.Quite different from the former cases,the effect of the strain along the zigzag direction on the band gap is decreased almost linearly in different range of the tensile strain.These changes of the electronic property of α-Si1C7-graphyne under uniaxial strain are remarkably distinct.Compared with such cases,this result reveals that a strain-induced electronic structure transition occurs in α-Si1C7-graphyne.