Ab initio studies on the geometrical and vibrational structures of polymers

The geometrical structures and vibrational spectra of all-trans, cis-transoid and trans-cisoid polyacetylene, and all-trans-polymethineimine have been calculated using the energy gradient scheme for one-dimensional polymers based on the ab initio crystal orbital method. The vibrational spectra of all-trans-polyacetylene reported here are in good agreement with the experimental results. We have proposed a reassignment of the Raman spectra of cis-transoid- polyacetylene. The vibrational spectra of the trans-cisoid polyacetylene are calculated theoretically. The bond alternant structure of all-trans-polymethineimine is more stable than the equidistant one, and the vibrational spectra are calculated for this structure.