Simple Huckel method applications

By far, the theoretical approaches that experimental inorganic chemists are most familiar with and in fact nse to solve questions qnickly and qnalitatively are the simple Huckel method and Hoffinann s extended Hiickel theory. These approaches are nsed in concert with the application of symmetry principles in the bnUding of syimnetry adapted linear combinations (SALCs) or gronp orbitals. The ab initio and other SCF procednres ontlined above prodnce MOs that are treated by gronp theory as well, bnt that type of rigor is not usually necessary to achieve good qnahtative pictures of the character aud relative orderiugs of the molecular orbitals. 

Molecular-orbital theory has taken many forms and has been dealt with by many approximations. In 1963 Hoffmann S presented a formalism which he referred to as extended Hiickel (EH). In the 1930 s, however, this formalism would simply have been called molecular-orbital, since it is a straightforward application of molecular-orbital (MO) theory, using a one-electron Hamiltonian. Hoffmann referred to it as extended Hiickel because it did not limit itself to 7r-electron systems and was able to deal with saturated molecules by including all overlap integrals. In these respects it did extend the usual, or simple Huckel, method, which was customarily applied to 7T-electrons, and assumed complete tt — a separability. 

HuLiS started as a Java applet and evolves to ajavascript/HTML5 script to increase the ease of use [33]. The program is available as a web application at http //ism2. univ-amu.fr/hulis, and can also be downloaded as a standalone java applet. The mobile version is available from the same address. In addition to the simple Huckel method, HuLiS implements the two methods described herein and the topological resonance module described in this section. 

The extended Huckel method, as simple as it is, has proven enormously successful in very many applications. Its successes depend on the fact that the Fock matrices have the correct symmetry properties and that the atomic potentials supplied through the use of experimental ionization potentials are more or less correct. Extended Huckel theory (EHT) calculations are still being performed today and yield results of interest in nearly all areas of chemistry and condensed matter theory.As this theory requires only ionization potentials and basis sets, it has been extended in one form or another to all elements of the... 

Pauling bond orders were correlated with experimental CC bond lengths in numerous benzenoid hydrocarbons and have offered insights into the variations in CC bonds in these molecules. Pauling bond orders found additional application in quantum chemistry whether used alone or combined with their counterpart in HMO, the Coulson bond orders [21], One such illustration, outlined in Chapter 3 in the section "The Difference in HMO and PPP Bond Orders showed that the differences between the simple Huckel MO calculations and more elaborate self-consistent-field MO calculations, known as the Pariser-Parr-Pople MO method [22], points to so-called Fries valence structures. These are Kekule valence structures that have the largest number of benzene rings with three C=C bonds [23]. Pauling bond orders continue to be of interest in structural chemistry. For example, recently S. Narita and... 

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