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First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in (111) orientation. By considering the spinâ€"orbit interaction, for stoichiometric surface, the topological states keep robust for six-bilayer case, and can be recovered in the three-bilayer film, which are guaranteed by time-reversal symmetry and inverse symmetry. For reduced surface doped by non-magnetic Bi or magnetic Mn atom, localized three-fold symmetric features can be identified. Moreover, band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom, while can be eliminated by adsorbed or substitutional magnetic Mn atom. [ABSTRACT FROM AUTHOR]

Study of the native defects in transition metal dichalcogenides (TMDCs) is of fundamental interest and potential technological importance. The atomic and electronic structures of native defects with charge states in ZrSe 2 are systematically investigated for the first time based on first-principles calculations with the optB86R-vdW and HSE06 functionals. We identify the configurations of relatively stable defects including Zr interstitial (Zr int), Se vacancy (V Se) and Zr antisite (Zr Se). The positive charged Zr interstitial defect (Zr int 2 +) has the lowest formation energy and thus is most commonly seen in ZrSe 2 , which is in good agreement with experimental observation. The Zr Se defect is found to form a DX-like configuration. Moreover, the non-interacting Zr Frenkel pairs are the most favorable form of intrinsic defects. The electronic structure analyses of these defects reveal that the extra Zr atoms adjacent to the defects act as donors, which are responsible for the native n-type conductivity of as-grown ZrSe 2. Our study can provide an insight into understanding the properties of native defects in ZrSe 2. • Native defects in ZrSe 2 are investigated for the first time by taking into account both the vdW and HSE06 functionals. • The atomic and electronic structures of native defects are discussed in detail. • Our results show that the native defects dominate the n-type doping of ZrSe 2. [ABSTRACT FROM AUTHOR]

The naturally grown Bi 2 Se 3 is always n -type doped by native point defects, although the p -type Bi 2 Se 3 is much desirable as a promising thermoelectric material and topological insulator. We use first-principles calculations to identify the origin of the n -type tendency in bulk Bi 2 Se 3 : The Se vacancies (V S e 1 and V S e 2) and Se B i antisite dominate the donorlike doping with low formation energy, while the predisposed Bi S e 1 defect results in the pair of V S e 1 and Bi interstitial, which is also a donor rather than an acceptor. For Bi 2 Se 3 (111) surface, by calculating the defect formation energy and surface charge density distribution, we find that the band structures modulated by the defects explicitly account for the existing experimental observations of n -type preference. Moreover, the topological surface states can be significantly affected by the n -type tendency of Bi 2 Se 3. • The Se vacancies and Se Bi antisite dominate the donorlike doping of Bi 2 Se 3. • The electronic structures of the native point defects are discussed in detail. • Surface charge density distributions of defected Bi 2 Se 3 (111) are presented. • Defects have dramatic influence on the surface states of Bi 2 Se 3. [ABSTRACT FROM AUTHOR]