Electronic Transmission Coefficient as a Tool for the Analysis of the Effect of Impurities and Defects on the Electronic Structure of Polymers

The effect of impurities and defects on the electronic structure of some polymeric chains has been approached by considering a model infinite chain ...AAAABAAAA..., where B is an impurity or defect embedded in an infinite chain ...AAAAA.... The transmission coefficient t(E) and differential density of states Delta DOSfE) curves have been used to characterize the different types of interactions between an impurity/defect level and an energy band. When the energy band can interact with more than one level of the impurity/defect, interference effects have to be considered. A rule to predict the constructive/destructive nature of these interferences is given. The use of the transmission coefficient as an analytical tool and the connection with the usual orbital interaction analysis of the electronic structure of molecules and solids are illustrated. The effect of several C=X impurities (X = O, S, CH2) and sp(3) defects as well as donor and acceptor pendant groups on the electronic structure of polyacetylene chains has been considered.