DEFECTIVE LATTICE CHARGE-DENSITY WAVES IN LA10SE19, CS3TE22, RBDY3SE8, AND DY65.33SE120

In this paper we consider charge density waves in defective lattice st ructures. Just as in nondefective lattices, we find that the Fermi sur face plays an important role in supercell dimensions. In particular, a correspondence is found between the Fermi surfaces of the defective a nd the nondefective lattices. The concept of an effective band filling is introduced, which may be understood as the band filling for which the fully occupied lattice mimics the Fermi surface of the partially o ccupied lattice. To demonstrate the efficacy of this method, the super structures of La10Se19, Cs3Te22, RbDy3Se8, and Dy65.33Se120 are studie d. Fermi surfaces from both Huckel and extended Huckel tight-binding t heories allow the rationalization of the defect lattice structures fou nd in these systems. Finally a simple model based only on nearest neig hbor interaction is found to preserve most of the essential features o f the Huckel and extended Huckel treatments.