Instabilities of the symmetry-adapted restricted-Hartree–Fock ground state in infinite polyenes. II. Nonsinglet instabilities

✍ Scribed by O. Castan̄o; P. Karadakov

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 712 KB
• Volume: 22
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/qua.560220213

✦ Synopsis

Abstract

The stability of the possible ground states of an infinite linear equidistant polyene model has been discussed in the PPP approximation of the unrestricted‐Hartree–Fock (UHF) method. The emphasis has been placed upon the investigation of nonsinglet (triplet) instabilities: the spin‐density waves (SDW's) and the spin‐bond‐order alternation waves (SBAW's). For physically realistic parameter sets the SDW ground state of the infinite linear equidistant polyene has been shown to be lowest in energy. Whereas the symmetry‐adapted restricted HF (RHF) solution (SAS) has been shown to be unstable to the formation of SDW's and SBAW's for all investigated parametrizations, the bond‐order alternation wave (BAW) solution has been found to be unstable to the formation of SDW's, but stable to the formation of SBAW's; in fact, the BAW's and the SBAW's have been shown to yield identical gap widths and ground‐state energies (at least in the PPP method). It has been shown that there exist such sets of semiempirical parameters for which the charge‐density wave (CDW) ground state is nonsinglet stable irrespective of the existence of an energetically advantageous SDW solution for the same parameter set.