Energy band structure of Bi12SiO20 and Bi12GeO20 single crystals

The energy band structures of the Bi12SiO20 and Bi12GeO20 single crystals 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 than 0.02 Ry. An agreement between the calculated reflection coefficient and the experimental optical reflection data was obtained. Moreover, a striking similarity of the Bi12SiO20 and Bi12GeO20 energy band structures was found. The local pseudopotential approach is suggested to be more effective than any nonlocal one in order to describe other complex single crystals.