Optical properties of Nb and Mo calculated from augmented-plane-wave band structures

Nonrelativistic band calculations of Mattheiss for Nb and Petroff and Viswanathan for Mo are used to calculate the imaginary part ε₂ of the dielectric function for these metals. The structure resulting from interband transitions in the frequency range 0.1-0.5 Ry is found to give fairly good agreement with experiment. The calculation indicates that structure in ε₂ can arise from transitions away from symmetry points and lines in the Brillouin zone. The difficulty in distinguishing between the direct and indirect transition models for ε₂ is shown to arise from a lack of strong optical critical points. Predictions of the rigid-band model for the optical properties of Nb-Mo alloys are presented.