HCl-doped conducting Emeraldine polymer studied by ab initio Car-Parrinello molecular dynamic

We present a Car-Parrinello molecular dynamics study of the highly conducting Emeraldine salt, which definitely settles the controversy between the polaronic and the bipolaronic lattice models present in the literature. Our treatment is fully microscopic and takes into account interchain interactions, individual chain conformation, and the dynamics of the HCl protonation. We have highlighted the peculiar role of the Cl- counterions both for the polymer structure and for the interpretation of its metallic character. Our study indicates that this metallic character is due to the pi electrons along each chain with chlorine counterions in polaronic arrangement and that only the Pc2a lattice symmetry provides an x-ray spectrum in complete agreement with the experiments.