The results for Bisanthene are summarized in Table and Figure . The corresponding HOMO-LUMO gaps are given in Table MP2 corrections) in Table give similar results for the energy differences, this is not true for the corresponding HOMO-LUMO gaps. As is shown in Table . the smallest gap is obtained by the non-hybrid PBE functional, known to significantly underestimate the gap; whereas the larger gap is obtained by the double hybrid functional. Table The distribution (and not necessarily the total number) of aromatic rings (i.e., the aromaticity pattern) is very important for the aromatic and electronic properties (including the stability) of such polycyclic structures. In fact, the actual aromaticity pattern can be "measured" by scanning tunnelling microscopy (STM), as was mentioned earlier. Gutman et al. have shown that the aromaticity pattern of (alternant) NGRs can be "measured" by examining the submolecularly resolved STM images which coincide with the corresponding aromaticity pattern (see for example their figure ). This is very important for our purposes (vide infra). Finally, it should be mentioned that the convergence of the open to the closed singlet state under geometry optimization which occur in bisanthene, does not occur in peri-tetracene (and other higher peracenes). Thus, the comparisons of the three spin states are not as straightforward as for bisanthene. However, as will be shown below, the conclusions are exactly the same. theoretical prediction can (and indeed is) experimentally verified by the comparison of the experimental STM images with the calculated aromaticity patterns for each candidate spin state, as we can see in Fig. . As we can see in Fig. , the "measured" STM image matches the aromaticity pattern of the closed singlet state, and clearly disagrees with the one of open singlet (and triplet). We can then conclude that the closed singlet state is the true spin state of peri-tetracene. Thus, we suggest here a new experimental verification of the closed singlet ground state of peri-tetracene (contrary to recent theoretical predictions), and at the same time a new method to safely predict the true spin state of benzenoid (alternant) NGRs and GNRs. As will be shown below in section 4, this is not true for non-alternant NGRs.