Based on a numerically highly accurate local-density-approximation (LDA) calculation, the authors present a k.p analysis of the interband optical absorption in YBa2Cu3O7 in the infrared region (h(cross)w<0.1 eV). It is shown that the LDA band structure gives rise to three infrared interband transitions: a sharp peak for the in-plane (E perpendicular to c) polarization at about 320 cm-1, a wide maximum for E mod mod c at about 420 cm-1, and a structureless absorption ( epsilon 2 approximately=const) for E mod mod c. The first feature is due to transitions between the apical-oxygen-derived bands, the second one to that between the z-even and z-odd CuO2 plane bands, and the third one to the transitions between the chain band and the z-odd plane band. The possibility of observing these features in experiment is discussed.
 

Physical Review B, 46 11232-5, 1992.