Electronic states in doped trans-polyacetylene: numerical simulation of half-filled systems

Abstract

Doped polyacetylene is simulated by the SSH model with a random distribution of impurities. Three types of impurities are examined. They are site- and two bond-types. One of the bond-types is named cis-type, since all the impurities are so assumed to modify the electron transfer that the dimerization is enhanced. The other is named compensated doping, since the half are for the enhancement while the other half are for reduction. Starting from a uniform dimerization, we determine the electronic states and the lattice configuration by an iteration method. Periodic boundary condition is relaxed so that the electronic wave function has a given phase difference between the left and right boundaries. The system is composed of one hundred (CH) units, electrons of the same number, and impurities of concentration up to eight percent. The sample averaging is performed over one hundred distributions of the impurities to confirm that the averaged order parameter and density of states well reproduce the results by the CPA calculations. The averaged order parameter is smaller than the impurity-free system with the site-type impurities and the compensated doping. It is larger with the cis-type impurities. With the site-type impurities, an impurity band is formed in the energy gap. With the cis-type doping, there is no impurity band. There are two in the compensated doping.