Electronic structure of amorphous germanium sulphides

First-principles calculations results are presented for the electronic structures of amorphous and liquid Ge-S. Model cluster calculation of the density of states using a geometry similar to that of the crystalline state coordination in GeS2 can reproduce the peak structure of the experimental valence band (VB) photoemission spectra. Conduction band densities of states are also calculated and their structure is interpreted together with the VB. The present calculations confirm that the states at the VB top are lone-pair states, and that the VB below them and the conduction band are bonding or anti-bonding states of the Ge-S bond. A definite shape of the molecular orbitals around the bandgap is also revealed. (C) 2002 Elsevier Science B.V. All rights reserved.