Single Slater determinant calculations have been done for the family of n-periacene molecules having n = 1-6, by applying both, the ab initio unrestricted Hartree-Fock (UHF) method, and a set of DFT functionals. The UHF results agree with previous DFT, exhibiting all of them (those for n = 1, 2 included) an anti-ferro magnetic polarized ground state. Moller-Plesset and CISD calculations have been carried out on the wave-functions previously found in the UHF calculations. All of them lead to an inversion in the relative stability found at the single Slater determinant level, predicting as the most stable the non-polarized closed shell state. (C) 2009 Elsevier B.V. All rights reserved.