DEFECT-INDUCED GAP STATES IN QUASI-ONE-DIMENSIONAL SYSTEMS

A simple scheme for estimating the single-particle energies of defect- induced states in quasi-one-dimensional systems from the band structur es of the defect-free systems is proposed. It is based on a transfer-m atrix formulation of the Schrodinger equation and is shown to be most valid for extended defects. A number of applications are presented, in cluding solitons, polarons, twistons, and ring-torsion defects in conj ugated polymers, solitons in hydrogen-bonded systems, structural and s ubstitutional defects in Se helices, and interfaces between crystallin e materials. The scheme provides thereby a unifying description of a l arge number of different defects.