Wannier functions characterization of floating bonds in a-Si

We investigate the electronic structure of over-coordinated defects in amor phous silicon via density-functional total-energy calculations, with the ai m of understanding the relationship between topological and electronic prop erties on a microscopic scale. Maximally localized Wannier functions (MLWF) are computed in order to characterize the bonding and the electronic proper ties of these defects. The five-fold coordination defects give rise to delo calized states extending over several nearest neighbors (NNs), and therefor e to very polarizable bonds and anomalously high Born effective charges for the defective atoms. (C) 2001 Elsevier Science B.V. All rights reserved.