Relativistic effects on the linear optical properties of Au, Pt, Pb and W

We report first-principles calculations of the linear optical properties for the metals gold, platinum, lead and tungsten. The dielectric functions are obtained within the independent particle approximation using Kohn–Sham energies and wavefunctions. We focus on the impact of spin–orbit coupling, but also investigate the role of the scalar-relativistic terms. The latter are crucially important to explain the absorption behavior and hence the color of gold. A detailed analysis of the oscillator strengths allows us to trace back the origin of the optical transitions within a given energy range to certain regions in the Brillouin zone. The four examples highlight the importance of relativistic effects that show up in different energy regimes of the optical spectra. Our results, not relying on any further approximation, allow us to judge the origin of the remaining discrepancies with experiment.