Physical properties of the body-centred tetragonal CaPd2Ge2

Abstract

We have investigated the structural, elastic, electronic, and lattice dynamical properties of CaPd2Ge2 in the body-centred tetragonal ThCr2Si2 structure using a generalised gradient approximation of the density functional theory and the ab initio pseudopotential method. The calculated second-order elastic constants indicate that CaPd2Ge2 is mechanically stable and behaves in a ductile manner. Our electronic results show that the states close to the Fermi level are primarily contributed by Pd d and Ge p orbitals. A detailed analysis of electron-phonon interaction calculations reveals that the mechanism for superconductivity in CaPd2Ge2 is mainly governed by interactions of Pd d and Ge p electrons around the Fermi level with acoustic phonon modes and low-frequency optical phonon modes, which strongly change PdGe4 tetrahedral bond angles. The values of the average electron-phonon coupling constant and the logarithmic average frequency are calculated to be 0.66 and 77.3 K, respectively. Inserting these values into the Allen-Dynes formula with using an acceptable value of mu* = 0.13 for the effective Coulomb repulsion parameter, the value of superconducting transition temperature is obtained to be 1.69 K, which is in excellent agreement with its experimental value.