Selfhyphen;Consistent Theory of Bond Alternation in Polyenes: Normal State, Chargehyphen;Density Waves, and Spinhyphen;Density Waves

摘要

The unrestricted Hartreendash;Fock theory is used to investigate bond alternation inC4Nplus;2H4Nplus;2cyclic polyenes. The possible ground states are examined as functions of the parameters in the Pariserndash;Parrndash;Pople model Hamiltonian. We show that chargehyphen;densityhyphen;wave ground states do not exist for physical values of the input parameters. The normal, or molecularhyphen;orbital, ground state does give rise to a negligible bond alternation at largeN, in agreement with previous workers. Spinhyphen;densityhyphen;wave ground states exist for most values of the parameters and have lower energy than the normal ground states. These states do not exhibit bond alternation when the sigmahyphen;bond compression is the same as that used to obtain the normal energy.