Heusler alloys with Mn and Co have been found to exhibit interesting electronic and magnetic properties. Mn 2 CoAl is well known SGS compound while Mn 2 CoGa has weak half metallic character. By using plane wave pseudo-potential method, we studied the effect of Fe and Cr doping on half-metalicity and magnetism of these compounds. The doping destroys the SGS nature of Mn 2 CoAl while the small-scale doping enhance the half-metallicity of Mn 2 CoGa making it perfect half-metal. In case of Mn 2 CoAl, the doping decrease the band gap while increase in band width is noticed for Mn 2 CoGa. The half-metallicity is destroyed in both cases when the doping level is beyond certain degree. Moreover, we have also computed magnetic behavior of Mn 2 CoZ alloys and we found that total magnetic moments of dopped samples have higher values than that of pristine compounds.

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We study the structural, electronic and magnetic properties of Co-based LiMgPdSn-types of quaternary Heusler compounds (CoFeCrAl, CoFeTiAs, CoFeCrGa, and CoMnVAS) using Density Functional Theory (DFT) implemented on Tight Binding Linear Muffin-Tin Orbital within Atomic Sphere Approximation (TB-LMTO-ASA) Code. The optimized value of lattice parameter for CoFeCrAl, CoFeTiAs, CoFeCrGa and CoMnVAs are found to be 5.61A˚, 5.76 A˚, 5.61A˚ and 5.71A˚ , respectively. From the calculation of electronic band structure and spin polarized total density of states (DOS), we found that CoFeCrAl and CoFeCrGa are spin-gapless semiconductors with halfmetallic gap of 0.82eV and 0.25eV respectively. CoFeTiAs half-metal (Nearly spin-gapless semiconductor) with half-metallic gap of 0.38 eV, and CoMnVAs is found to be nearly gapless halfmetal. Magnetic moment of these compounds almost obey the Slater-Pauling rules. All these compounds expected to have high curie temperature which makes them significant for spintroincs/magnetoelectroincs applications.

The Mott-insulator phase transition behaviour of the superstructure of strongly correlated system, CaxSr(1-x)VO3 (x =0, 0.33, 0.67, 1) have studied using the conventional density functional theory and the dynamical mean field theory. The Mott-Hubbard metal-insulator phase transition of superstructures, Ca0.33Sr0.67VO3 and Ca0.67Sr0.33VO3 formed by the CaVO3 and SrVO3 correlated metals, are obtained at U=4.5eV with β= 6(eV)-1 and U =4.5eV with β= 7(eV)-1 respectively. The values of U and β calculated through the Maximum Entropy model using the Green’s function data, are consistent with the experimental results. The value of Seebeck coefficient (S) of superstructure Ca0.33Sr0.67VO3 and Ca0.67Sr0.33VO3 are found to be +0.0011[V/K] and -0.0011[V/K] within the chemical potential  μ = -1.266 eV to μ = -0.938 eV. The figures of merit (ZT) are found to be 0.97 at room temperature for these systems. The variation of electrical and thermal conductivities has also been discussed.

The conventional density functional theory (DFT) and dynamical mean field theory (DMFT) is used to study the structural, electronic and the Mott-Hubbard metal-insulator phase transition of the pristine and superstructures, La(1-x)SrxTiO3 (x = 0, 0.20, 0.80, 1). The electrical and thermal conductivities, Seebeck coefficient, Figure of merit are calculated using the BoltzTraP codes. The present study reveals that the direct band gap of 2.20 eV and indirect band gap ~2.0 eV at the Γ point in the Brillouin zone of SrTiO3 is upgraded to 3.423eV by using modified Beck-Johnson (mBJ) interaction potential. The metal-insulator transition (MIT) of LaTiO3 and the superlattice La(1-x)SrxTiO3 have been investigated by using conventional density functional theory (DFT) and dynamical mean field theory (DMFT). The Mott-Hubbard metal-insulator transitions for pristine LaTiO3 for a Coulombian parameter, U = 2.5 eV and the thermodynamic parameter β = 6 (eV)-1 are consistent with the experimental results. A typical set of these correlation parameters for MIT La0.20Sr0.80TiO3 and La0.80Sr0.20TiO3 systems are found to be U = 3.5 eV and β = 10(eV)-1 and U = 3.2 eV and β = 10 (eV)-1 respectively. The characteristic sharp quasi-particle peak for a sample of La0.80Sr0.20TiO3 superlattice systems is obtained correlation parameter U = 3.0 eV and β = 6(eV)-1. A thermoelectric phase transition is observed for Seebeck Coefficient at temperature 300 K at near chemical potential, μ = 1eV of SrTiO3. The corresponding figure of merit (ZT) with chemical potential (μ) appears to be unity at near μ = 1eV.