Study of half-metallicity has been performed in a new series of Mn2ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U).

A first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. In addition, we have also revealed a new marcasite phase in RuS2, unlike most studied pyrite structures. The new phase has fulfilled all the necessary criteria of structural stability and its practical existence. The transition pressure of 8 GPa drives the structural change from pyrite to orthorhombic phase in RuS2. From the thermodynamical calculation, we have reported the stability of new-phase under various ranges of applied pressure and temperature. Further, from the results of phonon dispersion calculated at Zero Point Energy, pyrite structure exhibits ground state stability and the marcasite phase has all modes of frequencies positive. The newly proposed phase is a semiconductor with a band gap comparable to its pyrite counterpart but vary in optical absorption by around 106 cm−1. The various Ru doped structures have also shown similar optical absorption spectra in the same order of magnitude. We have used crystal field theory to explain high optical absorption which is due to the involvement of different electronic states in formation of electronic and optical band gaps. Lӧwdin charge analysis is used over the customarily Mulliken charges to predict 89% of covalence in the compound. Our results indicate the importance of new phase to enhance the efficiency of photovoltaic materials for practical applications.

A semimetallic type of electronic profile has been predicted for RFe4Sb12 (R = Pr, Nd) from a first-principles investigation, where the presence of a small energy bandgap above the Fermi energy level (EF) is a key feature. The EF lies at the top of the valence band and it is crossed by a single band more than twice, which improves the band concentration and electronic specific heat as reflected by the high Seebeck coefficient. The doping of a heavy lanthanide atom at the center of the cage formed by pnictogen atoms has a significant effect on the electronic structure that enhances the Seebeck coefficient and the thermoelectric power factor. The heavy atom at the center also dampens the lattice vibration and lowers the lattice thermal conductivity. The Nd-doped system shows an enhanced Seebeck coefficient with the highest power factor among the sample alloys. Moreover, due to significant reduction in the lattice thermal conductivity from 2.46 W/m K to 0.54 W/m K, a maximum ZT value of ∼1.11 at 800 K has been observed for an Nd-doped system. The covalent nature of PrFe4Sb12, Pr-doped NdFe4Sb12, and Nd-doped PrFe4Sb12 and the ionic nature of NdFe4Sb12 have been confirmed, where Pr-doped NdFe4Sb12 is the stiffest and a highly rigid material with strong bonding forces among the constituent atoms. The results presented in this manuscript open the possibilities for further exploration of center atom-doped filled skutterudites with improved Seebeck coefficient and reduced lattice thermal conductivity, which are promising materials for thermoelectric applications

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The electronic and magnetic properties of Mn2ZnSi(1−x)Gex (x = 0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0) inverse Heusler alloys and Mn2ZnSi/Mn2ZnGe superlattice have been investigated using first-principles calculations.

Ab initio study on the family of ternary copper chalcogenides Cu 3 TaX 4 (X = S, Se, and Te) is performed to investigate the suitability of these compounds to applications as photovoltaic absorber materials. The density functional theory based full potential linearized augmented plane wave method (FP-LAPW method) is employed for computational purposes. The electronic structure and optical properties are determined including electron–electron interaction and spin–orbit coupling (SOC), within the generalized gradient approximation plus Hubbard U (GGA+ U ) and GGA+ U +SOC approximation. The large optical band gaps of Cu 3 TaS 4 and Cu 3 TaSe 4 considered ineffective for absorber materials, and also the hole effective mass has been modulated through applied pressure. These materials show extreme resistance to external pressure, and are found to be stable up to a pressure range of 10 GPa, investigated using phonon dispersion calculations. The observed optical properties and the absorption coefficients within the visible-light spectrum make these compounds promising materials for photovoltaic applications. The calculated energy and optical band gaps are consistent with the available literature and are compared with the experimental results where available.

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A theoretical investigation of electronic and magnetic properties has been performed on the new members of Heusler alloys M2NiZ (M = Sc, Ti, and V; Z = Tl and Pb) that crystallize in an inverse Heusler XA structure. The overall electronic properties and magnetic moments are predominated by M atoms, where the total magnetic moment varies linearly with the number of valence electrons, following the Slater–Pauling rule with ferro- or ferri-magnetic ground states. Their Curie temperatures are well above the room temperature and are comparable to analogous compounds. Among the sample alloys, Sc2NiTl, Ti2NiTl, and Ti2NiPb are half-metals, whereas V2NiTl has a nearly half-metallic profile that can be tuned into novel half-metal under uniform strain. Their thermodynamic, mechanical, and dynamical stabilities are also verified from their formation energy, elastic constants, and phonon spectra, respectively. A strong correlation between the directional elastic sound velocities and spatial dependence of elastic moduli is also observed. The evaluated Poisson's ratio from elastic constants and charge density plots predicts the partial ionic nature of Ti2NiTl and Ti2NiPb and the covalent nature of Sc2NiTl and V2NiTl. The optical phonon modes are found to be both Raman and infrared active, whereas the reststrahlen band is observed in the far-infrared region.