Calculation of optical spectra of aluminum

The electronic structure and optical properties of aluminum were studied using the augmented-plane-wave (APW) method. To improve the agreement between the calculated electronic structure and experiment a semiempirical scheme of Chen and Segall was used to adjust the band structure. This parametrization was implemented by employing a few pieces of experimental data on de Haas-van Alphen cross sections, the position of a major optical peak and the bandwidth of A1. The parametrized bands and wave functions were used in a calculation of the dielectric constant of A1 in which the dipole matrix elements were included. The spectrum was analyzed with regard to the origin of structure in $\overrightarrow{\mathrm{k}}$ space, with major structures treated analytically using the pseudopotential model. A novel aspect of this work is the elucidation of small-frequency behavior of the imaginary part of the dielectric constant which was shown to be nonzero at low frequencies due to an accidental degeneracy (in the absence of spin-orbit splitting) of the bands on the $\Gamma \mathrm{KWX}$ plane. The calculated spectrum is in very good agreement with optical data with respect to the location, strength, and width of major structures. A comparison between momentum matrix elements calculated by the pseudopotential and APW method is presented.