We have carried out an ab initio study of the electronic, vibrational and electronphonon interaction properties of the body-centred tetragonal CaIrSi 3 by employing the density functional theory, a linear-response formalism, and the plane-wave pseudopotential method. The electronic structure and phonon dispersion relations of this material have been analyzed with and without the inclusion of spin-orbit interaction (SOI). Our electron-phonon interaction results reveal that Si-related phonon modes are more involved in the process of scattering of electrons than the remaining phonon modes due to considerable existence of the Si 3p states near the Fermi level. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter is found to be 0.58 which compares very well with its experimental value of 0.56. Using the calculated value of λ, the superconducting critical temperature (T c ) for CaIrSi 3 is found to be 3.20 K which is in good accordance with its experimental value of 3.55 K. Furthermore, we have shown that the effect of SOI on the values of λ and T c is very small.

We have presented the structural, elastic, electronic, phononic, and electron-phonon interaction properties of the La-based noncentrosymmetric superconductors, such as LaIrSi 3 , LaRhSi 3 , and LaPdSi 3 , by using the generalized gradient approximation of the density functional theory. The calculated elastic constants reveal the mechanical stability of all the studied compounds in their noncentrosymmetric structure, while the lack of inversion symmetry gives rise to lift the degeneracy of their electronic bands, except in the C-Z and X-P directions. The calculated Eliashberg spectral function shows that all phonon branches of these materials couple considerably with electrons, and thus, all of them make contribution to the average electron-phonon coupling parameter k. Using the calculated values of k and the logarithmically averaged phonon frequency x ln , the superconducting critical temperature T c values for LaIrSi 3 , LaRhSi 3 , and LaPdSi 3 are estimated to be 0.89, 2.56, and 2.40 K, respectively, which accord very well with their corresponding experimental values of 0.77, 193904-2Uzunok et al.