Calculated electronic properties and reflectivity of tantalum

A nonrelativistic band structure of the bcc transition metal tantalum has been calculated by an iterative empirical-pseudopotential method. Main peak locations in the density of occupied states agree to better than 0.3 eV with the results of two earlier augmented-plane-wave calculations, while the main peak in the density of unoccupied states is more than 1 eV lower than the main peak in either of the previous results. In the context of direct transitions, the constant-matrix-element approximation is shown to be generally valid for Ta. In addition, reflectivity spectra based on the $\overrightarrow{\mathrm{k}}$-dependent, direct transition model, and the nondirect transition model have been calculated, and each spectrum is in comparably good agreement with the data of Weaver, Lynch, and Olson. Modulated reflectivity spectra have also been calculated according to both models, and the results suggest that measurements of this quantity might help to determine which of the two types of transitions—direct or nondirect—predominates in Ta. Finally, the calculated Fermi surface agrees well with the data of Halloran et al.