A SEMIEMPIRICAL MODEL STUDY OF THE ELECTRONIC AND LATTICE STRUCTURE OF A PRESSURE-QUENCHED SE-TE MIXED-CRYSTAL

The electronic and lattice structure of a pressure-quenched Se-Te mixe d crystal was studied using a CNDO-type semi-empirical model. The fund amental structure without any superlattice modulation gives nine p ban ds. Three of these have large dispersions along the b axis and the oth ers have small dispersions in all directions. The former bands form si x planar Fermi surfaces which nest with one another. This produces a s table 9 x 2 superlattice structure with a glide reflection symmetry, i n which wedge-like trimers are formed by shifts of the atoms. The supe rlattice structure can be regarded as a quasi-one-dimensional system c omposed of 2/3, 5/9, and 7/9 filled chains along the b axis.