Predicted modifications in the direct and indirect gaps of Ge

The charge density of Ge was studied at various k-points and for various ba nds, by the ab initio pseudopotential method, using additionally the inters titial sites. The lowest X-c conduction-band points were found to be unique in having a high charge density in the interstitial site. It has been ther efore predicted and verified that the X-c points move up in energy relative to the Gamma(c) point when closed-shell atoms (like H) are substituted at the interstitial sites. The calculations also indicate the change of the ba nd-gap for HGeH. (C) 2000 Elsevier Science B.V. All rights reserved.