GAP STATES AND LOCALIZED ORBITALS IN QUASI-ONE-DIMENSIONAL SYSTEMS

We propose a simple scheme for estimating energies at which localized orbitals induced by interfaces, solitons, polarons, domain walls, twis tons, ring-torsion defects, etc., may be found. It is based on the pro perties of defect-free chains described within the single-particle app roximation. It is argued that the scheme is most correct in the limit of very delocalized defects. A number of examples of applications are presented, whereby results for many different systems are given a unif ying description.