Iterative Extended Huckel

All valence electron (AVE) calculations (simultaneous treatment of tr- and ir-electrons) Three treatments (i) EHT (extended Hiickel theory) (ii) lEHT (iterative extended Huckel theory) (iii) CNDO treatment (an SCF MO type) 68MI40908 68MI40907 69MI40907... 

Koopmans theorem values are given in parentheses b Iterative Extended Huckel Theory (IEHT)... 

Haskins (Ref 9c) has compared molecular orbital calcns of some azides and tetrazoles with expl behavior, dipole moments, and binding energies. He used an iterative extended Huckel molecular orbital approach to calculate dipole moments of l-(H)tetrazole, 2-(H)tetrazole, and 5-aminotetrazole and found good agreement with exptl measurements. For example, l-(H)tetra-zole was calculated as 5.269p and measured as 5,1 Ip. Binding energies calcd by the similar extended Huckel molecular orbital (EHMO)... 

In 1976 Leban et used this approach to study the interaction of a platinum electrode with several particles, among them the water molecule and halide ions. The cluster used was taken to be a model of the Pt( 111) surface and contained only five platinum atoms. In this work the iterative extended Huckel molecular orbital (lEHT) method was used. The stability of the adsorption of the water molecule and of the ions was tested by computing the charge transfer to the cluster and the total energy of the system for various positions of the adsorbate on the surface. 

Zalis and Vlcek studied the electronic structure of [M(mnt)2]" (M = Co, Ni or Cu n = 1, 2 or 3) by semiempirical methods. Iterative extended Huckel methods (lEHT) and CNDO results were compared. Except for [Co(mnt)2f , both methods yielded as the HOMO for all d complexes for the exception, CNDO found 10, as the HOMO. lEHT and CNDO revealed a greatly reduced... 

In the extended Huckel method, the repulsion which the electron experiences from electrons on neighboring atoms is supposed to be cancelled by the attraction with the nuclei. In addition, the electron-electron interactions on one atom are averaged or simulated by an electron density-dependent term (iterative extended Huckel). 

In semiempirical MO-LCAO calculations of any type, for instance the iterative extended Huckel (lEH) type , the charges on atoms, and more specifically their electronic configurations, are usually calculated by means of a Mulliken population analysis. (Other population analyses may also be efficient). For instance, for the p-electron density on atom A we have ... 

The Huckel methods perform the parameterization on the Fock matrix elements (eqs. (3.50) and (3.51)), and not at the integral level as do NDDO/INDO/CNDO. This means that Huckel methods are non-iterative, they only require a single diagonalization of the Fock (Huckel) matrix. The Extended Huckel Theory (EHT) or Method (EHM), developed primarily by Hoffmann again only considers the valence electrons. It makes use of Koopmans theorem (eq. (3.46)) and assigns the diagonal elements in the F... 

In analogy to extended Huckel theory, there are also charge iterative methods for simple Huckel theory. The equivalent of eq. (3.90) is... 

Extended Huckel Molecular Orbital (E.H.M.O.) calculations employed the ICON 8 program with the standard basis set of the valence orbitals and electrons of the elements present. All Hjj s were charge iterated. The experimental models, with full molecular symmetry were used in all calculations. 

Finally, within the crystal-orbital formalism for the valence electrons one can also use the extended Huckel method of Roald Hoffmann that leads to extended Huckel band structures of quasi-one-dimensional periodic chains. Unfortunately, we cannot here enter into the details of this method (neither in its simple nor in its iterative form). 

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