Electronic structure and electron-phonon interaction in hexagonal yttrium by density functional calculations

To understand the pressure-induced changes in the electronic structure and the electron-phonon interaction in yttrium, we have studied hexagonal-close-packed (hcp) yttrium, stable at ambient pressure, and double hexagonal-close-packed (dhcp) yttrium, stable up to around 44 GPa, using density-functional-based methods. Our results show that as one goes from hcp yttrium to dhcp yttrium, there are (i) a substantial charge transfer from s -> d with extensive modifications of the d band and a sizable reduction in the density of states at the Fermi energy, (ii) a substantial stiffening of phonon modes with the electron-phonon coupling covering the entire frequency range, and (iii) an increase in the electron-phonon coupling constant lambda from 0.55 to 1.24, leading to a change in the superconducting transition temperature T-c from 0.3 to 15.3 K for mu(*)=0.2.