The First Principle Study Of New Two-dimension Telluride

The representative of two-dimensional(2D)materials(graphene)has aroused a wave of research in many fields,such as nanoelectronics and nanomaterials.Compared with bulk materials,they have potential research and applications in electronics,energy storage and energy utilization due to their unique structure and electronic properties.In this thesis,we first introduce the development of 2D topological insulators and low-dimensional charge density wave materials.In chapter two,we introduce in detail the basic theories and calculation methods,including density functional theory and Wannier function.These theories and calculation methods provide the basis for the implementation of our work.In chapter three,we predict that the monolayer AuTe₂Cl is a quantum spin Hall(QSH)insulator with a topological band gap about 10 me V.The three-dimensional(3D)AuTe₂Cl is a topological semimetal that can be viewed as the monolayer stacking along b axis.By studying the energy level distribution of p orbitals of Te atoms for the bulk and the monolayer,we find that the confinement effect driven p^-_y-p⁺_z band inversion is responsible for the topological nontrivial nature of monolayer.Since 3D bulk AuTe₂Cl has already been experimentally synthesized,we expect that monolayer AuTe₂Cl can be exfoliated from a bulk sample and the predicted QSH effect can be observed.In chapter four,we report a compound of quasi-2D divalent rare-earth telluride EuTe₄which exhibits a striking semiconducting behavior in charge density wave(CDW)state.The high temperature structure contains consecutive near-square Te sheets.Upon cooling,the compound experiences a phase transition near 255 K.The low temperature structure reveals strong structural distortions showing a 1a×3b superstructure with a periodic formation of Te trimers in the monolayer Te sheets,yielding evidence for the formation of CDW order.based on the density functional theory(DFT)calculations.The modeling indicates that the FS topology favors a nesting vector along the b-axis direction with a value of q=b^*/3(where b^*=2?/b),which is quite well consistent with the experimental observations.Our result suggests a nesting-driven CDW phase in EuTe₄,which lowers the electronic energy of the system and is responsible for the semiconducting properties.In the last Chapter,we make a conclusion of this paper and give some future prospects for our work.