We perform ab initio calculations within the local density approximation for infinite, isolated chains of poly(para-phenylene) (PPP) and poly(para-phenylene-vinylene) (PPV). Phonon frequencies at →k=→0 and structural properties are investigated with special focus on the ring-torsion barriers. Our results for PPV indicate a planar geometry, while for PPP we find a ring-torsion potential that is not affected by next-nearest-neighbor rings. This suggests the existence of a multiply degenerate ground state for PPP, with chiral, ordered, or random angle-alternating configurations having the same energy. In addition, we couple these results to a simple molecular-dynamics simulation in order to investigate the finite temperature behavior of the systems.
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Capaz et al. (2003) studied this question.
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