VIBRATIONS AND SOLITON DYNAMICS OF POSITIVELY CHARGED POLYACETYLENE CHAINS

Ab initio molecular dynamics simulation is performed on a small polyac etylene chain with a positive soliton defect. The dynamics is initiali zed by an external electric field. The collective motion of the carbon and hydrogen atoms are compared to some low frequency vibrational mod es of positively charged polyacetylene chains of varying lengths havin g the characteristics of the soliton displacement. The soliton effecti ve mass estimated using a variety of schemes is found to be about 10 e lectron masses. The static linear polarizability of singly charged pol yacetylene chains of varying lengths is computed and compared with tha t of undoped chains, The electronic contributions to the polarizabilit y are computed at the level of the coupled Hartree-Fock or the random phase approximation, and the vibrational contributions are estimated b y invoking the double harmonic oscillator approximation. The soliton d efect causes some enhancement of the electronic term, which covers 10- 15 carbon-carbon double bonds, and it generates a large increase of th e vibrational part, which in the absence of counter ions show no sign of leveling off even for the longest chains considered. (C) 1997 Ameri can Institute of Physics.