Ab initio investigations of phonons and superconductivity in the cubic Laves structures LaAl2 and YAl2

We have performed an ab initio study of structural, elastic, electronic, lattice-dynamical, and electron-phonon interaction properties of the cubic Laves structures LaAl2 and YAl2. The calculations have been carried out within the density-functional theory and linear response formalism using pseudopotentials and a plane-wave basis. The calculated phonon dispersion relations for both materials accord very well with experimental data available for the principal symmetry directions. The average electron-phonon coupling constant lambda is found to be 0.35 for YAl2 and 0.65 for LaAl2. Thus, our results indicate the superconducting transition temperature is very low for YAl2 but a superconducting transition temperature T-c of around 3 K for LaAl2 is found with mu* = 0.16. Finally, we have observed that the soft phonon modes related to the vibrations of La atoms play a dominant role in the superconductivity of LaAl2. (C) 2012 American Institute of Physics. [doi:10.1063/1.36813271]