Band structure and optical properties of ordered AuCu3

The optical spectra of ordered Au${\mathrm{Cu}}_3$ have been measured at low temperatures by a direct ellipsometric technique. We find several structural elements above the absorption edge as well as in the infrared. The measured spectra are interpreted in terms of the interband absorption calculated from an ab initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered Au${\mathrm{Cu}}_3$ has distinct copper and gold $d$ bands positioned in and hybridizing with an $s$ band common to copper and gold. The calculated state density is found to be in good agreement with experiment. The Fermi surface is presented and is found to originate mainly in copper $4s$ and $4p$ states.