CALCULATIONS ON CRYSTAL DEFECTS IN TRANSPOLYACETYLENE

A number of studies were focused on the structure and morphology of po lyacetylene. But there is still a lack of reliable structural data cau sed by the difficult morphology and disorder of this material. There a re two possible space groups fitting the experimental data of polyacet ylene, P 2(1)/a and P 2(1)/n. A controversy appears also about the und erstanding of the doping and dedoping of this system. For instance, di fferent doping levels may result in structural changes and disorder. T o study the influence of the morphology on X-ray measurements we did c omputer simulations of different crystal defects. Depending on whether the bond alteration is in phase or out of phase on neighbouring chain s, the (001) reflection is strongly allowed or forbidden. Random orien tation of the chains requires the orthorhombic space group P nam. Ther efore, we concentrate on the change of the calculated intensity of the (001) reflection as a function of the artificially introduced disorde r. We show calculations based on the three space groups P 2(1)/a, P 2( 1)/n and P nam.