Dynamical properties of the hexagonal close-packed metals Sc, Y, and Ru

In this paper we perform a comparative study of the dynamical response of the three hexagonal close-packed metals Sc, Y, and Ru for small- and medium-sized wavevectors up to 50 eV. The calculations are based on ground states which are determined using ab initio pseudopotentials together with a plane-wave expansion of the wavefunctions. We consider many-body as well as crystal local-field effects which both turn out to be small. In all of the three elements we find a strong anisotropy of the response with respect to the direction of the wavevector transfer. Furthermore, we obtain almost undamped plasmon excitations for small wavevectors in the direction normal to the hexagonal planes for the response of Sc and Y.