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Abstract In this paper, four types of compounds are considered: ideal wurtzite (B N), N vacancies in B N (B N − V N), A l doped ideal B N (A l : B N) and A l doped B N with N vacancies(A l : B N − V N). The structural, electronic and magnetic properties are calculated by using the density functional theory (DFT) based on the generalized gradient approximation implemented in Quantum-Espresso code. Our results show that the nitrogen vacancies and the aliminium impurities are responsible of the magnetic properties in these compounds. We have also found that aluminium impurities have a remarkable effect on the optical band gap. Our results are in good agreement with experimental and other theoretical studies. We can conclude from this study, that this material can be used as diluted magnetic semiconductors. Highlights • The DFT method has been used to study the Al doped (w−BN). • The lattice parameters increase with the incorporation of Al in the BN supercell. • The Al impurities decrease the value of the band gap. • Al and N vacancy induce magnetic properties. [ABSTRACT FROM AUTHOR]

In this paper, the manipulative effect of N doping on topological insulator Bi 2 Se 3 was investigated by using density functional theory (DFT). The computational results reveal that the van der Waals (vdW) correction is necessary when calculating the geometric structure of Bi 2 Se 3. Taking into account the spin–orbit coupling(SOC), the electronic structure of Bi 2 Se 3 can be accurately described, especially for the energy bands near the Fermi level. The N doping at anion sites can produce an impurity band which appeared at Fermi energy. Comparing with pure Bi 2 Se 3 , the electronic structure of N doping Bi 2 Se 3 changed obviously at Fermi energy. The valence band and conduction band meet when N doped on Se1 sites, the insulating properties of Bi 2 Se 3 system are damaged. The indirect gaps between the valence band and conduction band are 0.135 eV and 0.115 eV with N doping on Se2 sites with the doping levels 6.67% and 1.67%, respectively. On the other hand, the N doping at Se sites of Bi 2 Se 3 can induce magnetic moments. The magnetic moments are related to the covalent bond length between N atom and Bi atom. Furthermore, the real and imaginary parts of dielectric functions have been computed. The static dielectric constant ε 1 (0) becomes significantly larger and the peaks in the imaginary part of dielectric constant ε 2 (ω) spectra move toward low energy. The intensity of the peak is gradually enhanced and there is a small bump in Bi 6 Se 8 N2 at 0.38 eV. The N doping paves a prospective way to tune the topological properties and may find change to potential spintronic applications and electronic devices. • The electronic structure of N doping Bi 2 Se 3 are changed obvious at fermi energy. • The insulation properties of Bi 2 Se 3 system are damaged with N doping on Se1 sites. • The N doping at Se sites can induce magnetic moments. [ABSTRACT FROM AUTHOR]