Electron-phonon coupling and spin fluctuations in 3d and 4d transition metals: implications for superconductivity and its pressure dependence.

We have calculated the electron-phonon coupling for the complete 4d series and the nonmagnetic 3d transition metals using the linear response method and the linear muffin-tin orbitals' basis. A comparison of the linear response results and those obtained via the rigid muffin-tin approximation is provided. Based on the calculated values of the electron-phonon coupling constants, band density of states and the measured values of the electronic specific heat constants, we estimate the spin-fluctuation effects, i.e. the electron-spin-fluctuation (electron-paramagnon) coupling constants in these systems. For the sake of comparison, several other metals, Cu, Zn, Ag, Cd, Al and Pb, are also studied. Alternative estimates of the electron-paramagnon coupling constants are obtained from the values of the Stoner parameters and the band densities of states at the Fermi level. Implications of these results on the superconductivity and its pressure dependence as well as the alloying effects of superconductivity in these systems are discussed. It is pointed out that spin fluctuations play an important role in the validity of the Matthias rule that in metallic systems the optimum conditions for (electron-phonon) superconductivity occur for 5 and 7 valence electrons/atom.