ELECTRONIC BAND-STRUCTURE AND UNOCCUPIED DENSITY OF STATES FOR YBAS AND YB4AS3

The one-electron energy band structure for YbAs and Yb4As3 is calculated up to 1.5 Ry above the Fermi energy by a self-consistent augmented plane wave (APW) method with the local density approximation. The calculated unoccupied density of states is compared with the observed bremsstrahlung isochromat spectroscopy (BIS) spectra. In YbAs, two peaks appear at about 5.5 and 10 eV above the Fermi energy, in good agreement with the experimental result. These originate from the Yb 5d and the Yb 5d-As 4p antibonding states, respectively. In Yb4As3, a broad peak originating from the Yb 5d states combined with the antibonding state appears at about 5.5 eV above the Fermi energy. The discrepancy between calculated and observed peak positions is due to the valence fluctuation.