Trapping and hopping of bipolarons in DNA: Su-Schrieffer-Heeger model   calculations
  With the Su-Schrieffer-Heeger model involving the effects of solvent polarization and external electric field, we show that bipolaron maybe more stable than two polarons when a dication induced into a DNA stack. Under the high electric field, the dication can move quite a long distance through the DNA by a series of hopping process, partially losing its configuration instantaneously due to the nonadiabatic effects. 
J. H. Wei, L. X. Wang, K. S. Chan and YiJing Yan