DYNAMICS OF PRISTINE AND DOPED POLYACETYLENE - A COMBINED INELASTIC NEUTRON-SCATTERING AND COMPUTER-SIMULATION ANALYSIS

A characterization of the dynamics of trans-polyacetylene in its prist ine form and doped with sodium at 12.5 at. % is presented. The results of inelastic neutron scattering experiments are compared with the low -frequency density of vibrational states calculated from molecular dyn amics simulations. The anisotropy of the pristine trans-polyacetylene density of states is quantitatively reproduced by the simulations; a d ecomposition of the principal motions involved is presented. For the d oped system, complete ionization of the sodium ions was assumed, the c harge being uniformly distributed over the carbon atoms. It was found that the sodium ions perform low-frequency oscillatory motions with a rigid-body character parallel to the channel direction. The rigid-body motion occurs in the same frequency range as rigid-body motion of the chains. The results should be useful aids in theoretical investigatio ns of the influence of the large-amplitude modes on conduction propert ies.