HCl-doped conducting Emeraldine polymer by ab-initio Car Parrinello Molecular Dynamics

The HCl acidification process of the three dimensional Emeraldine Base II polymer is studied by means of Car-Parrinello Molecular Dynamics. Following X-ray experimental suggestions we have considered different starting simulation cells belonging either to the P21221 or to the Pc2a space groups. We have found that only the Pc2a primitive cell with chlorine counterions inserted in polaronic positions can reproduce the X-ray experimental spectrum; moreover, the backbone nitrogen atoms of each polymer chain are arranged on a plane, all the rings of the protonated chains assume the same character intermediate between benzenoid and quinoid, and all the nitrogen imine groups become nitrogen amine groups. Our study definitely supports the metallic character of the ES-II polymer as due to the Pi-electrons along each chain with chlorine counterions in polaronic arrangement. The presence of Cl- - -H---N hydrogen bonds has also been highlighted.