Hiickel band calculation

Hiickel band calculations, rigid-rod transition metal-acetylide polymers, 12, 371-372 Human health, tin toxic effects, 12, 637 Hybrid magnets, metallocene-containing bimetallic M(II)—Cr(II) oxalates, 12, 427 bimetallic M(II)-Fe(III) oxalates, 12, 432 bimetallic M(III)-Ru(III) oxalates, 12, 435 materials, 12, 437 properties, 12, 425 trimetallic oxalates, 12, 436 Hydantoins, with lead reagents, 3, 888 Hydration... 

A theoretical study of a variety of tricyclic polymers with different types of bridging groups has been performed for the fused bithiophene system (Figure 9). Geometrical structures of the polymers were obtained from semi-empirical SCF band calculations and the electronic properties from the modified extended Hiickel band calculations <1997PCB10248, 1997JCP(107)10607>. 

The anions located in centrosymmetrical cavities lie slightly above or below the molecular planes. This structure results in a dimerization of the intermolecular distance (overlap) with a concomitant splitting of the HOMO conduction band into a filled lower band separated from a half-filled upper (holelike) band by a gap at 2k% called the dimerization gap which is shown in Fig. 6 at the point X of the new Brillouin zone. However, on account of the transverse dispersion, this dimerization gap does not lead to a genuine gap in the density of states as shown from the extended-Hiickel band calculation (Fig. 7). The only claim which can be made is that these conductors have a commensurate band filling (3/4) coming from the 2 1 stoichiometry with a tendency towards half... 

Since 1987 calculations have been done on a variety of systems, some of which had previously been prepared and others that were predicted to have low band gaps. Some of these predicted systems were subsequently prepared, whereas others remain unknown. Thus, the pyrrole polymer derivative of 22 (.v = y = 1), namely 23, was calculated (MNDO geometry/Hiickel band calculations) to have a band gap of 0.99 eV [64] and 1.10 eV using MNDO geometry and VEH band structure calculations [65]. A related vinylogous system (24) was calcu-... 

The pyrrole analogs of the polybenzo-, polynaphtho-, and polyanthrothiophenes, 1, 16, and 18, namely, 29, 30, and 31, were calculated (MNDO geometry/Hiickel band calculations) [70], and the more stable form in these cases is the aromatic rather than the quinonoid form. The band gaps were calculated for the planar and non-... 

A series of extended Hiickel theory (EHT) band calculations on crystal structures 16 and 17 have been performed <2003JA14394, 2004CM1564>. They show that the dispersion curves plotted along the stacking direction arise from the SOMOs of the radicals in the cell unit, that is, the putative half-filled conduction band of the molecular metal. Clearly, none of the materials are metallic, but the dispersion curves nonetheless provide insight into the extent of the intermolecular interaction along and perpendicular to the slipped 7t-stacks. 

Because only little direct evidence for the conformation of the phytochrome chromophore is available mainly theoretical calculations and measurements with model pigments are discussed here. Burke et al.22) were the first to apply Hiickel MO calculations to the problem to the conformation of the phytochrome chromophore. They pointed out that not the band position as such but the ratio of the oscillator strength of the long-wavelength band (fx) and the short-wavelength (f2) allows the best verifi-... 

The molecular arrangement in the crystals of neutral [Ni(tmdt)2] is illustrated in Figure 4.28 the [Ni(tmdt)2] molecules are ideally flat and closely packed. Three-dimensional short S - S contacts develop within the structure. The conductivity at room temperature is 4 x 10 S cm and it shows metallic behaviour (Figure 4.28). The band calculations based on first principle calculations and extended Hiickel tight-binding calculation... 

The transverse magnetoresistance measurements on a Type A sample showed a saturation at around 10 Tesla, and a decrease up to about 20 Tesla [34]. SdH oscillations are superposed on this background magnetoresistance above 20 Tesla (Fig. 21). The oscillation period is 0.0015 T-i. The band calculation, based on the extended Hiickel MO, shows that the Fermi surface of this salt is composed of 2D closed (hole like) and ID surfaces (Fig. 9) [23]. The area of the extremal orbit calculated from the SdH oscillation (16.5% of the first Brillouin zone) is comparable to that of the closed Fermi surface in Fig. 9 (19%). More precise measurements on the magnetoresistance and other properties are underway. 

Suppose we wish to compare the calculated energy of regular polyacetylene to that of a bond-alternating version, or that of PPP with PPP-N2. How do we get energies from the band calculations for these two cases In a Hiickel-type calculation of a molecule, we simply add up the one-electron energies. In a band calculation we are faced with a very large set of one-electron energies—one for each k value. How do we deal with this ... 

Almost a decade ago, we wrote a report on Special Project Research on New Superconducting Materials carried out at that time [17], in which our motivation, to use a simple extended Hiickel tight-binding band calculation, was briefly described. Since the chemical viewpoint on the usefulness of the simple band examination mentioned there seems to still be valid, it might be permissible to quote some sentences from it. 

Extended Hiickel gives a qualitative view of the valence orbitals. The formulation of extended Hiickel is such that it is only applicable to the valence orbitals. The method reproduces the correct symmetry properties for the valence orbitals. Energetics, such as band gaps, are sometimes reasonable and other times reproduce trends better than absolute values. Extended Hiickel tends to be more useful for examining orbital symmetry and energy than for predicting molecular geometries. It is the method of choice for many band structure calculations due to the very computation-intensive nature of those calculations. 

YAcHMOP stands for yet another extended Hiickel molecular orbital package. The package has two main executables and a number of associated utilities. The bind program does molecular and crystal band structure extended Hiickel calculations. The viewkel program is used for displaying results. We tested Version 3.0 of bind and Version 2.0 of viewkel. 

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