The imaginary part of the dielectric constant ${\epsilon }_2$ has been calculated for Cu, Ag, and Au in the energy range $\hslash \omega \le 25$ eV with full inclusion of momentum matrix elements and spin-orbit effects. The calculations were performed by a second-principles method using a combined interpolation scheme. Overall agreement with experiment, both with regard to positions and intensitites of structures, is quite good, especially for Cu and Au. Band-by-band decompositions of ${\epsilon }_2$ are presented and are used to locate prominent structures in $\overrightarrow{\mathrm{k}}$ space. In the case of Au, the prominent transitions seen in thermoreflectance data around 20 eV are shown to occur at the $L$ point (or possibly at the $X$ point) rather than at the zone center as previously proposed.

• Received 23 October 1980

DOI:https://doi.org/10.1103/PhysRevB.24.1895