Dynamics of polaron pairs in BOW and SDW backgrounds

Dynamics of a pair of polarons with like charges and antiparallel spins in the bond-order-wave (BOW) background is numerically studied using the extended Peierls-Hubbard model for trans and cis isomers of polyacetylene. The unrestricted Hartree-Fock approximation is used. An (fictitious) spin-dependent electric field is introduced to the system so that the polarons approach each other and collide together. In the case of the trans isomer, the polarons separate into a soliton and an antisoliton after the collision. The breather is left behind. In the case of cis isomer, the polarons make a bound state, bipolaron. The excess energy (the energy difference between the polaron pair and the bipolaron) is transferred to phonons localized around the bipolaron. The results in the spin-density-wave (SDW) background are also summarized and compared with the present results.