Plasmon dispersions in simple metals and Heusler compounds

Abstract

We present a comprehensive study of plasmon dispersions in simple metals and Heusler compounds based on an accurate ab initio evaluation of the momentum- and frequency-dependent dielectric function $\ensuremath{\varepsilon}(\stackrel{P\vec}{q},\ensuremath{\omega})$ in the random-phase approximation. Using a momentum-dependent tetrahedron method for the computation of the dielectric function, we extract and analyze ``full'' and ``intraband'' plasmon dispersions: The ``full'' plasma dispersion is obtained by including all bands, the intraband plasma dispersion by including only intraband transitions. For the simple metals silver and aluminum, we show that the intraband plasmon dispersion has an unexpected downward slope and is therefore markedly different from the results of an effective-mass electron-gas model and the full plasmon dispersion. For the two Heusler compounds ${\mathrm{Co}}_{2}\mathrm{Fe}\mathrm{Si}$ and ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Si}$, we present spectra for the dielectric function, their loss functions, and plasmon dispersions. The latter exhibit the same negative intraband plasmon dispersion as found in the simple metals. We also discuss the influence of spin mixing on the plasmon dispersion.