The polarization of closed shells in an alternant polyene radical due to the field of its unpaired electron is discussed. It is shown that the Hartree–Fock solution is unstable relative to a small perturbation caused by polarization of closed shells in a long polyene radical. Its ground state is found to be antiferromagnetic with a forbidden zone in the spectra of one-particle excitations.
Yuri A.Kruglyak, I.I.Ukrainsky
Study of the Electronic Structure of Alternant Radicals by the DODS Method
Intern. J. Quantum Chem. IV(1), 57 - 72 (1970)