Extended Huckel molecular orbital

The substrate in these studies was restricted to be rigid, and Morse functions were used for the hydrogen-surface and two-body interactions. The parameters in the Morse functions were determined for single hydrogen atoms adsorbed on the tungsten surface by fitting to extended Huckel molecular orbital (EHMO) results, and the H2 Morse parameters were fit to gas-phase data. The Sato parameter, which enters the many-body LEPS prescription, was varied to produce a potential barrier for the desorption of H2 from the surface which matched experimental results. 

In this section we mention the paramagnetic monocationic complexes [Mo(CO)2(dppe)2]+ and [Mo(CO)2(bipy)2]+, both of which are produced by oxidation of the parent Mo° complexes. In the former case, the oxidants used include [MeCftKUNJfBFj,46 NO[PF6], I2 and AgIla-47 and a variety of analogues [Mo(CO)2L2]+ has been obtained (L2 - dppm, dmpe, diars, etc.).1 47 Electrochemical oxidation has also been used, with other measurements, to show that a rapid cis — trans isomerization follows oxidation and an explanation for this phenomenon has been proposed on the basis of extended Huckel molecular orbital calculations, the stereochemical change being dependent on the number of valence electrons and the nature of the coligand jr-donor or -acceptor capacity. Similar studies have been made upon the compounds [Mo(CO)2L2]+ (L = bipy or phen).47... 

Chemisorption state modeling by extended Huckel molecular orbital calculations were made in a collaborative study with R. M. Gavin, and full details of these calculations will be published elsewhere. 

Electronic band structures were calculated for several polymeric chains structurally analogous to polyacetylene (-CH-CH) and carbyne (-CbC). Ihe present calculations use the Extended Huckel molecular orbital theory within the tight binding approximation, and values of the calculated band gaps E and band widths BW were used to assess the potential applic ilitf of these materials as electrical semiconductors. Substitution of F or Cl atoms for H atoms in polyacetylene tended to decrease both the E and BW values (relative to that for polyacetylene). Rotation about rhe backbone bonds in the chains away from the planar conformations led to sharp increases in E and decreases in BW. Substitution of -SiH or -Si(CH,) groups for H in polyacetylene invaribly led to an increase in E and a decrease in BW, as was generally the case for insertion of Y ... 

Fig. 5.1. Experimental P-O bond length versus bond overlap population calculated using extended Huckel molecular-orbital theory. See Bartell et al. (1970) for further details (after Bartell et al., 1970 reproduced with the publisher s permission).

Bartell, L. S., L. S. Su, and H. You (1970). Lengths of phosphorous-oxygen and sulfur-oxygen bonds. An extended Huckel molecular orbital examination of Cruickshanks dTr-dit picture. Inorg. Chem. 9, 1903-12. 

Recent evidence favors Dg symmetry and a pentagonal bipyramidal structure for the heptafluoride. Claassen et al. (2) review the earlier debate about structure of lower symmetry. They provide convincing evidence of D symmetry from the first observation of Raman spectra of the vapor state and re-examination of the infrared spectra. Their data—including five fundamentals in Raman (two polarized), five fundamentals in infrared, no coincidences between Raman and infrared, and one fundamental inactive—are consistent only with symmetry. This is confirmed by Falconer et al. (4) who interpret their electric-deflection experiments as indicating a symmetry-forbidden dipole moment. Extended Huckel-molecular-orbital calculations (5) also predict Dg symmetry. The adopted structural parameters are from our approximate analysis of the electron-diffraction data of Thompson and Bartell (6). The authors gave a radial distribution curve and suggested only a gross (unrefined) structure because of the probable presence of... 

The methylidyne cubane [Cp Ti(/x-CH)]4 (Scheme 202) is obtained as a dark brown crystalline solid by thermolysis of Cp TiMe in toluene with methane elimination. This transformation was monitored by NMR and no intermediates are observed. The signals assignable to the methylidyne groups appear as singlets at 6 17.75 in the NMR and at 6 490.8 in the 13C NMR spectra. In order to analyze the interaction between the /i3-ligand and the titanium centers, extended Huckel molecular orbital calculations have been carried out. In contrast, the thermolysis of the trinuclear oxo alkyls [Cp Ti(/i-0)(CH2R)]3 (R = H, Me) affords the //3-alkylidyne derivatives [Cp Ti(//-0)]3-(/x3-CR).505-507... 

REX relativistically extended Huckel molecular orbital theory... 

The fact that the electrochemical oxidation of cis-[M2(cp)2(/x-SR)2(CO)4] and of [M2(/i-SR)2(CO)8]2 is reversible despite the amount of structural reorganization involved suggests that these changes require low activation energy. Extended Huckel Molecular Orbital (EHMO) calculations on the model complex (R = H) indicated that the Lowest Unoccupied Molecular Orbital (LUMO) was the u Mo—Mo [ 1- Weakening of the... 

Fig. 4. Electron exchange between iron cations in (Fe06)n octahedra clusters calculated by extended Huckel molecular orbital theory (from [21] and [22].

ECP (Effective Core Potential) 171 Effective pair potential 68 EHMO (Extended Huckel Molecular Orbital Model) 130 Eigenvalue 17 Eigenvector 17 Einstein relation 253 Electric dipole moment 100, 265, 282 Electric field gradient 278 Electric moments 184 Electric quadrupole moment 268, 269 Electric second moment 268 Electric susceptibility 256 Electron affinity 147 Electron correlation 186, 273 Electron density 100, 218, 222 Electron relaxation 118 Electron spin 91, 95, 99, 277, 305 Electronic Schrodinger equation 74 Electrostatic field 14 Electrostatic field gradient 271... 

EHMO extended Huckel molecular orbital (quantum chemical method)... 

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. 

Extended Huckel molecular orbital calculations were used to obtain an initial, qualitative picture of the electronic structure changes involved in two-electron transfer. EHMO calculations were carried out in D2h symmetry on H2P" bridged analogs of the [M2(p-PR2)2(CO)8] complexes using the CACAO program (50). Structural information and computational details are provided in reference 18. 

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