POLYCARBONITRILE - A SYNTHETIC METAL

First-principles calculations on the electronic properties of polycarb onitrile - a compound closely related to trans polyacetylene - have be en carried through. The lowest total energy for the neutral, undistort ed system is found for a structure with a C-N bond-length alternation, although also structures without this alternation have a gap at the F ermi level. Subsequent model calculations predict solitons but not pol arons to be stable for the charged and photoexcited chains. Solitons i nduce two roughly symmetrically placed gap states. Polycarbonitrile sh ould thus be considered a synthetic metal and might moreover be intere sting in non-linear optics.