Investigating superconductivity in body centered tetragonal structures using density functional theory

Immediately after the discovery of superconductivity near 15 K in YNi2B2C, there has been continued and increasing interest in borocarbide superconducting materials. Many experimental and theoretical works have been made for the discovery of new borocarbide superconductors with higher transition temperature (Tc) values. At the end, new borocarbide superconductors with ThCr2Si2-derivative structure (LuNi2B2C structure) indicating high Tc values have been discovered. Among these materials, the highest Tc value of 23 K has been observed for YPd2B2C. Thus, ThCr2Si2 type intermetallics have been studied due to their superconducting and magnetic properties. Type-II superconductivity has been reported for SrPd2Ge2 (Tc near 3 K), which has ThCr2Si2-type structure. This superconductor seems enchanting as compared to Fe-based superconductors because the magnetic metal (Fe) is replaced by the nonmagnetic metal (Pd). This has led to the discovery of type-II superconductivity in SrPd2As2, BaNi2P2. Several experimental studies have been made to obtain superconducting parameters of these superconductors. The experimental works have provided impetus for theoretical studies of the structural and electronic properties of these materials. In order to achieve a better understanding of superconductivity in these materials, phonon properties of them must be studied experimentally as well as theoretically because the source of superconductivity is almost exclusively the electron-phonon interaction. To the best of our knowledge, theoretical investigation of the electron-phonon interaction in these superconductors has not been made. Thus, the source of superconductivity in these superconductors are still lacking in the literature. The goal of this thesis is to make the state-of-the-art investigations of the structural and electronic properties of the superconductors BaNi2P2, BaRh2P2, BaIr2P2, LiCu2P2, SrPd2Ge2, SrPd2As2, CaPd2Ge2, CaPd2As2, LuNi2B2C, ScNi2B2C, La3Ni2B2N3 and Bi2Pd by employing the plane wave pseudopotential method and density functional theory. With the availability of these results, a linear response method will be applied to study phonons in these materials. Moreover, we will carry out ab initio calculations of electron-phonon interaction for these materials in order to calculate their superconducting parameters such as the density of states at the Fermi level (N(EF)), the Eliashberg spectral function (α2F(ω)), the electron-phonon coupling parameter (λ), the electronic specific heat coefficient (γ) and superconducting transition temperature (Tc). Using the calculated superconducting parameters, we will try to explain the physics of superconductivity in these superconductors.