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We present an analysis of bulk and surface electronic structures of thallium based ternary III-V-VI2 series of compounds TlMQ2, where M=Bi or Sb and Q=S, Se or Te, using the ab initio density functional theory framework. Based on parity analysis and (111) surface electronic structure, we predict TlSbSe2, TlSbTe2, TlBiSe2 and TlBiTe2 to be non-trivial topological insulators with a single Dirac cone at the Γ-point, and TlSbS2 and TlBiS2 to be trivial band insulators. Our predicted topological phases agree well with available angle-resolved photoemission spectroscopy (ARPES) measurements, in particular the topological phase changes between TlBiSe2 and TlBiS2. Moreover, we propose that Weyl semimetal can be realized at the topological critical point in TlBi(S1−xSex)2 and TlBi(S1−xTex)2 alloys by breaking the inversion symmetry in the layer by layer growth in the order of Tl-Se(Te)-Bi-S, yielding six Dirac cones centered along the Γ − L directions in the bulk band structure.

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We demonstrate room temperature ferroelectricity in the epitaxial thin films of magnetoelectric

We present a theoretical study of the structure-property correlation in gallium ferrite, based on first-principles calculations followed by a subsequent comparison with experiments. The local spin density approximation (LSDA + U ) of the density functional theory has been used to calculate the ground state structure, electronic band structure, density of states and Born effective charges. The calculations reveal that the ground state structure is orthorhombic Pc2 1 n having A-type antiferromagnetic spin configuration, with lattice parameters matching well with those obtained experimentally. Plots of the partial density of states of constituent ions exhibit noticeable hybridization of Fe 3d, Ga 4s, Ga 4p and O 2p states. However, the calculated charge density and electron localization function show a largely ionic character of the Ga/Fe-O bonds which is also supported by a lack of any significant anomaly in the calculated Born effective charges with respect to the corresponding nominal ionic charges. The calculations show a spontaneous polarization of ∼59 μC cm −2 along the b-axis which is largely due to asymmetrically placed Ga1, Fe1, O1, O2 and O6 ions.

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