The PSO Structure Prediction And Properties Calculation Of Novel Pentagonal Two-dimensional Materials

Since the single-layer graphene was prepared by mechanical peeling in 2004,two-dimensional materials have been a popular research field.Graphene has attracted widespread attention due to its high mobility,high strength,high thermal conductivity and easy peeling.However,the application of graphene in semiconductor materials is limited by its zero band gap.In 2015,a new single-layer two-dimensional carbon material,penta-graphene,was successfully developed by the Peking University team using first-principles calculation.The penta-graphene not only has super-high mechanical strength comparable to graphene,but also has a large intrinsic band gap,which perfectly solves the problem of zero band gap of graphene.Inspired by the above work,this thesis employed particle swarm optimization（CALYPSO）to predict a series of two-dimensional single-layer pentagonal structures,and then adopted the first-principles calculation to predict the stability of new structures.For the stable structures,the mechanical and photoelectric properties of the structure are tested by the first-principles calculation based on density functional,and the application prospects of the new two-dimensional layered materials are further explored.Finally,for each structure,the suitable experimental substrates are tested and the possible synthesis reaction is predicted,which provides theoretical basis for the preparation and synthesis of new materials in the laboratory.Specific research contents are as follows:1.Particle swarm optimization（CALYPSO）is used to predict the pentagonal two-dimensional structure obtained by orthogonal experiments of IV family（C,Si,Ge,Sn）and V family（N,P,As,Sb）elements.The dynamic and thermal stability of pentagonal two-dimensional structures are predicted by phonon spectrum calculation and molecular dynamics simulation.At the same time,the mechanical and photoelectric properties of the stable two-dimensional structures are calculated systematically.The simulation results show that the strength of the two-dimensional structure is slightly lower than that of graphene,which is equivalent to that of black phosphorus,but the flexibility of the two-dimensional structure is greatly improved.In terms of photoelectric properties,this kind of pentagonal two-dimensional structure have indirect band gaps ranging from 1.36 eV to 2.72 eV（HSE）,and the band gaps are adjustable via external strain,which can realize the property transition from metal to semiconductor.The band characteristics can be widely used in the design and development of semiconductor devices.2.The pentagonal two-dimensional single-layer structure composed of Pt and other V-group elements（P,As,Sb）is systematically studied by element replacement method.Similarly,the mechanical and photoelectric properties and experimental possibilities of the stable structure are systematically and comprehensively predicted and calculated by first-principles calculation.The results show that the mechanical stability of the two-dimensional structure is good,and its mechanical strength is better than that of the pentagonal two-dimensional structure composed of IV and V elements.And this kind of structures have direct band gaps ranging from 0.13 eV to 0.53 eV（HSE）,which is different from the first series structures.Moreover,the direct band gap is adjustable under the applied strain,remaining a direct band gap unchanged.The conversion of properties between metals and semiconductors can also be realized.3.The experimental substrates MgF₂ and MgAl₂O₄ suitable for the growth of folded pentagonal single-layer two-dimensional structure SiP₂ and pure planar pentagonal single-layer two-dimensional structure PtP₂ were found,respectively.And the suitable synthesis reaction was predicted theoretically,which provided theoretical basis for the experimental synthesis.