ENERGY-BAND STRUCTURE OF BI12SIO20 AND BI12GEO20 SINGLE-CRYSTALS

The energy band structures of the Bi12SiO20 and Bi12GeO20 single cryst als were calculated using a local pseudopotential method. An iteration procedure was carried out by use of increasing number of plane waves (up to 1500) until the required energy eigenvalue stability was less t han 0.02 Ry. An agreement between the calculated reflection coefficien t and the experimental optical reflection data was obtained. Moreover, a striking similarity of the Bi12SiO20 and Bi12GeO20 energy band stru ctures was found. The local pseudopotential approach is suggested to b e more effective than any nonlocal one in order to describe other comp lex single crystals.