First-principles Study Of Electronic Structure Modulations In Novel Three-dimensional Materials

Electronic structure is essential in determining the application of materials.Modulating the electronic structure can change the intrinsic properties to obtain the promising performances in materials.Firstly,half-Heusler semiconductors with the total valence electron number of 18 have drawn great attention in optoelectric and thermoelectric fields.The accurate bandgaps for these semiconductors can effectively guide their practical application.Thus,we correct the bandgaps for 27 recently reported half-Heusler semiconductors XYZ with HSE06 hybrid functional.In addition,the inversion of band ordering can occur in half-Heusler compounds with specific constituent elements,indicating the topologically nontrivial phase,which is expected in spintronics.Here,we design the half-Heusler superlattice Lu Au Sn/Lu Pt Bi to study the tuned band inversion by Lu Pt Bi layer number.Finally,we investigate the variations of electronic and magnetic structures for bcc Gd under pressure to further understand the strong correlation in lanthanides.The main results of this thesis are listed as follows:1.The bandgaps for half-Heusler semiconductors XYZ are increased with HSE06 hybrid functional,where the increment of bandgap is determined by the energy separation between the two lowest conducting bands.In addition,an abnormal behavior that the bandgap decreases with the Pauling electronegativity difference between the atoms on Z-and X-sites is observed,arising from the delocalization of the charges on Y-site.2.[111] Lu Au Sn/Lu Pt Bi superlattice is relatively stable in structure.When the Lu Pt Bi layer number increases,the band inversion is enhanced for [111] Lu Au Sn/Lu Pt Bi superlattice,arising from band alignment,internal electric field and quantum confinement.3.The magnetic moment for bcc Gd decreases with pressure,which results from the charge transfer from the spin-up channels with higher energies to the spin-down 4f channels with lower energies.When pressure reaches around 90 GPa,the magnetic transition from ferromagnetic to [011] antiferromagnetic phase is observed.