Extended Hiickel methodology

Polyacene (50) calculations have been carried out by a number of different methods, which, depending on the geometry, have given different values for the band gap. Extended Hiickel methodology gave values of 0.45 and 0.002 eV, respectively, for 50a and 50b [2]. In this case... 

In Sect. 5.3 that follows, we report on the electronic structural characteristics of the C-based hexagonite structure from the point of view of the extended Hiickel molecular orbital method (EHMO), which is an approximate solid state electronic structure algorithm based upon the tight binding methodology (Hoffmann 1963 ... 

This situation prompts a theoretical investigation of the problem. So far, the only available computation was carried out for the isolated molecule by the extended Hiickel Theory (51) and it predicts as the most stable conformation of the free zwit-terion the completely extended one. Because of known limitations of this methodology which lead frequently to erroneous results we have reinvestigated the problem by more refined quantum mechanical procedures. We have also distinguished explicitly between the study of the free molecule and the molecule in solution. 

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