ON THE STABILITY OF POLYYNE

Results of first-principles, density-functional calculations on two interacting, parallel chains of polyyne are reported. The total energies indicate the existence of a (meta)stable configuration consisting of two crosslinked linear chains. This agrees with experimental findings that polyyne undergoes slow crosslinking if the interchain reactions are sterically possible. For slightly larger interchain distances the calculations predict that the chains prefer a zigzag structure and this may be the stable structure for a multichain system. The band structures indicate that the system changes from semiconducting to metallic upon reduction of the interchain distance. This agrees with the experimentally observed decrease of the energy onset of UV-VIS absorption and increase of electronic conductivity upon aging.