Impurity effects on solitons in conjugated polymer linking model hamiltonians and ab initio method descriptions

Conducting polymers present an enormous gamma of technological applications. Polyacetylene is the best studied conducting polymer and the presence of topological defects in the bonding conjugation called solitons is known to be associated with the principal properties of the material. The charge and bond length structure of a single polyacetylene chain with soliton trapped at impurities is investigated. As general model Hamiltonian we use the Su-Schrieffer-Heeger model combined with the Pariser-Parr-Pople model, with site type impurities. AM1 and PM3 semi-empirical and ab initio methods calculation as well as the B3LYP density functional calculation are performed with various radical molecules bonded to the polymer chain with a soliton. Actually, we have performed the calculations using the radicals NO, CH3, CN, I3, I, NF2, NH2, NHCH3, NO2, NCH2, IH2, K, Li, and Na. The charge density distributions associated with the soliton in the quantum chemistry calculations and the model calculation are presented. We found what radical molecules actually correspond to the charge distribution and bond length variations obtained with model calculations. Therefore, it is shown, within the present results, what impurities are being represented in model calculations.