DYNAMICS OF SOLITONS IN POLYACETYLENE IN THE STEP-POTENTIAL MODEL

In treating the motion of solitonic exitations in polyacetylene Newton 's equation is used to approximate the lattice dynamics. The force fie ld is obtained from the deviation of the pi-electron densities in the bonds from their equilibrium densities. The pi-electron density distri butions are evaluated with the step-potential model. This model of a n early free pi-electron coupled to the elastic lattice of sigma-bonded hydrocarbon ions is the conceptually simplest approach and has no free parameters. The electron-phonon coupling constant is scaled to butadi ene and benzene. It is shown that a neutral kink moves frictionless fo r velocities up to three times the velocity of sound and shakes off ph onons at higher velocities. This is in contrast to the results of the SSH-model, where the maximum velocity of the neutral kink is expected to be in a considerable range (0.6-4.0 times velocity of sound) depend ing on adjustable parameters.