EFFECTS OF LONG-RANGE POTENTIALS BY IMPURITIES IN POLYACETYLENE

Existence of nearly free solitons is numerically shown when dopant con centration is less than a critical value which is between 1% and 2%. T aking into account the structure of the Na-doped polyacetylene, observ ed at 6.67%, we assume a weakly random distribution of the dopants at lower concentrations. They have a long-range potential. Bond configura tion and excess electron density are determined for each sample of ran dom distribution. Distribution of potential variation is calculated, t ogether with the phonon density of states and infrared absorption spec tra. Below the concentration 1%, translational mode of the nearly free solitons strongly contributes to the spectra. At the concentration hi gher than 2%, no free charged solitons are found. It indicates the fac t that there is the critical concentration between 1% and 2%.