Using first principle electronic structure calculations within density functional theory and the supercell model, we have investigated the nature and formation energies of defect states associated with Ga and Te vacancies and Ge and Sn substitutional impurities in GaTe. We have also calculated the band structure of pure GaTe for comparison with systems with defects and also to find out the importance of spin–orbit interaction (SOI) on its band structure. We find that the top valence band at the Γ-point shifts up in energy by 0.1 eV due to the mixing of Te p x –p y and p z bands, this splitting being considerably smaller than in atoms where it is 0.8 eV. From an analysis of charge densities and band structures associated with the defect states, we find that most of them are strongly localized and lie deep in the band gap region. The calculated binding energy of the deep defect state and the ε(−1 / −2) transition level associated with the Ga vacancy appears to be in good agreement with experiment. Formation energy calculations suggest that V Ga is the preferred intrinsic defect in GaTe.

%B Journal of Physics: Condensed Matter %V 21 %P 015504 %G eng %0 Journal Article %J Journal of Physics: Condensed Matter %D 2008 %T Theoretical studies of defect states in GaTe %A Rak, Zs %A S. D. Mahanti %A Mandal, Krishna C %A Fernelius, N.C. %B Journal of Physics: Condensed Matter %V 21 %P 015504 %8 01/2009 %G eng %N 1 %0 Journal Article %J Physical Review B %D 2006 %T Ab initio studies of the electronic structure of defects in {PbTe} %A Salameh Ahmad %A S. D. Mahanti %A Khang Hoang %A M. G. Kanatzidis %XUnderstanding the detailed electronic structure of deep defect states in narrow band-gap semiconductors has been a challenging problem. Recently, self-consistent ab initio calculations within density functional theory using supercell models have been successful in tackling this problem. In this paper, we carry out such calculations in {PbTe,} a well-known narrow band-gap semiconductor, for a large class of defects: cationic and anionic substitutional impurities of different valence, and cationic and anionic vacancies. For the cationic defects, we study the chemical trends in the position of defect levels by looking at series of compounds {RPb2n−1Te2n,} where R is vacancy or monovalent, divalent, or trivalent atom. Similarly, for anionic defects, we study compounds {MPb2nTe2n−1,} where M is vacancy, S, Se or I. We find that the density of states near the top of the valence band and the bottom of the conduction band get significantly modified for most of these defects. This suggests that the transport properties of {PbTe} in the presence of impurities may not always be interpreted by simple carrier doping (from bound impurity states in the gap) concepts, confirming such ideas developed from qualitative and semiquantitative arguments.

%B Physical Review B %V 74 %P 155205 %8 10/2006 %G eng %N 15 %0 Journal Article %J Journal of Physics A: Mathematical and General %D 2006 %T The ground state of chargeless fermions with finite magnetic moment %A S. D. Mahanti %A Sudhanshu S. Jha %XWe consider the ground state of a system of chargeless fermions, such as neutrinos, of mass m and magnetic moment m interacting through long-range magnetic dipole interaction, within the framework of a {Hartree-Fock} variational approach. At high densities the uniform paramagnetic state becomes unstable towards a ferromagnetic state with quadrupolar deformation of the Fermi surface. The exchange energy which is attractive dominates the repulsive kinetic energy. If we let the density be a variable, then above a certain density the system will collapse to an infinite density state unless another short-range interaction stops the collapse. In the case of large deformations, the possibility of a purely dipolar deformation exists.

%B Journal of Physics A: Mathematical and General %V 39 %P 1239–1249 %8 02/2006 %G eng %N 6