Theoretical Study Of Low-Dimensional Transition Metal Dichalcogenides,Oxides,Phosphorene And Blue Phosphorus

The development of the material marks the progress of human society.With high-performances of graphene in the research field,the novel nanomaterial entered the era of rapid development.In order to overcome the shortcomings of the graphene-zero band gap,the similar structure of graphene and other low-dimensional nanomaterials have continued to attract significant interest from researchers worldwide.Two-dimensional(2D)materials have the thickness of one or few atomic layers,usually present the van der Waals interlayer interaction,and have markedly different electrical and photoelecltric properties than their bulk counterparts due to the quantum confinement effect.Therefore 2D materials show great potential for application in electronic,optoelectronic and thermoelectric devices.One-dimensional(ID)nanomaterials is the ideal system for studying transfer behavior,physical properties such as optics,magnetism and relations between size and dimension.ID nanomaterials play an important role in constructing nano electronic and optical device.As determinate structures and controlled performance,low-dimensional nanomaterials have a great chance to become the important carrier of future energy and information technology.In this paper,by using first principles,we performed theoretical studies on the potential applications of some newly synthesized or predicted low-dimensional nanomaterials in lithium-ion battery,sodium-ion battery and tuning properties.The main contents include:1.Research of 2D MnO2 as cathode for lithium-ion battery.At the time lithium insert into cathode,electron transfer from Li atom to the nearest 0 atoms and the orbital coupling between the s orbital of the Li atom and pz orbital of the O atom.MnO2 only needs to overcome a negligible energy barrier of?0.15 eV for the diffusion of Li atom.Moreover,when the MrnO2 monolayer reaches the highest Li concentration,the Li adsorption energy can be still as high as 2.89eV with a theoretical capacity of 616 mAh/g.Our results strongly suggest a monolayer or few-layer of MnO2 to be a promising cathode material for LIB s with excellent electrochemical performance in the near further.2.The realization of a widely tunable Eg in BP:By means of the doping Alkali-metal atoms.A free-standing phosphorene monolayer is a semiconductor with a direct band gap of 0.89 eV at G point,and Eg of BP depends sensitively on the number of layers in a few-layer slab.Charge transfer from the adatom to the phosphorene layer.By means of the doping Alkali-metal atoms on phosphorene,Eg could be reduced due to the shifting down of CBM means n-type doping because alkali-metal atoms donate electrons to the empty band of the phosphorene.Eg reduce obviously with increasing dopant concentration,and a SMT discovered in some critical dopant concentrations.Our theoretical results strongly suggest that the purpose of tuning band gap of BP can be realized by means of the doping Alkali-metal atoms.3.The influence of point defects on electronic properties of Blue phosphoras.The formation energy of various types point defect were distinguishing,separated from 1.58 eV to 2.86 eV,which means defects existed steadily in blue phosphoras.The diffusion barrier of single vacancy is only 0.34 eV,means high mobility.In addition,the surface is easy to attract additional phosphorus atoms,the migration of such defects need to overcome the energy barrier of 0.18 eV.The introduction of various kinds of defects diminished their band gap.We provide a fundamental research about various point defects in blue phosphorous,it will further promote to design the potential application of these materials in the experiments.4.Research of amorphous MoS3 as anode for Sodium-ion battery.Contrary to the well-studied 2D layered MoS2,amorphous MoS3 consists of ID Mo chains bridged by sulfide and disulfide ligands.Such a unique molecular structure leads to improved electrochemical performance with large specific capacity,excellent rate capability,and satisfactory cycling stability at both low and high current rates——reatly outperforming all existing MoS2-based electrode materials.Our DFT calculations showing that the ID molecular chains provide more open sites for Na? adsorption,and have a smaller Na?ion diffusion barrier.