Study On The Electronic Structure Of Low Dimensional Transition Metal Dichalcogenides WTe₂ And TiSe₂

Transition metal dichalcogenides WTe2 and TiSe2 are studied by using the first principle.Firstly,for the WTe2 nanoribbons,the properties of the elec-=tronic structures are mainly studied.The different boundary nanoribbons of 2H and Td phase crystal structures are established and optimizated.The stability of nanometers can be defined through the edge enenrgy,and the properties of the electronic band structures are calculated and analyzed.The data show that the Tdy boundary nanoribbons is the most stable one and approximate to structure of two dimensional monolayer.In the Tdx exist a 0-0.32 eV adjustable band gap with width.In 2Harmchair nanoribbons,the band gap is regulatable with width of Nanobelt.The Tdy and 2Ezigzag shows the metal properties and structure is quite similar to two-dimensional plane.In WTe2,one side band gap can be adjusted in nanoribbons and the other side is pure metal,which is of great significance in the practical application of WTe2.Secondly,for TiSe2,the effect of pressure and electron doping on the phase transformation of a charge density Wave is mainly studied.The electron and hole doping both inhibit the conversion of charge den-sity wave state of TiSe2.And when the lattice constant is stretched or compressed,charge density wave was enhance and weaken respectively.It is demonstrated that two critical points of the charge density wave and the ordinary phase in TiSe2.In the charge density wave state of TiSe2,the modulation by lattice compression will reduce the critical value of the doping stability,while the lattice tension will enhance the critical value of the doping stability.The normal TiSe2 will peak at 0.04 of the lattice compression.The results are of great significance for the study of transition metal sulfides.