On the actual nature of the anti-ferromagnetism shown by unrestricted calculations on conjugated hydrocarbon rings
Departamento de Química Física, Unidad Asociada del CSIC and
Instituto Universitario de Materiales, Universidad de Alicante,
San Vicente del Raspeig,
Received in final form: 23 June 2011
Published online: 29 September 2011
Unrestricted Hartree-Fock (UHF) calculations with spin-polarisation, plus Møller-Plesset (MP) perturbative corrections, have been applied to the study of the first four molecules of the family of n-acenes and also to the ground state of cyclobutadiene. The results are similar to those previously obtained for n-periacenes, which describe anti-ferromagnetic spin-polarised electronic structures. The projection to pure spin states gives results that recover the usual description of these molecules, i.e., non spin-polarised ground states. Extended coupled cluster calculations reinforce the projected results, also giving non spin-polarised ground states.
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2011