Ab initio investigations of phonon anomalies and superconductivity in the rock-salt YS

Abstract

The phonon spectrum, phonon linewidths and electron-phonon coupling parameter for YS have been calculated by using a first-principles scheme, based on the application of the plane-wave pseudopotential method, density functional theory, and a linear response technique. Our phonon results confirm the presence of anomalous features in the neutron-scattering spectrum for the longitudinal acoustic branch. It is shown that the electronic d-state effects are primarily responsible for the anomalous phonon behaviour. The calculated values of phonon linewidths along various symmetry directions are presented and discussed. The longitudinal acoustic phonon linewidth shows a maximum at the zone boundary L where the branch exhibits a pronounced dip. The calculated electron-phonon coupling parameter, lambda = 0.52, compares very well with a previous empirical value of 0.56.