Extended Hiickel tight binding

Based on the extended Hiickel tight-binding method the 2D energy dispersion relation and FS of k-(ET)2Cu(NCS)2 [29, 155, 161, 162] and K-(ET)2l3 [147, 163] have also been calculated. Figure 2.19 shows the results. The band structures are very similar except for the degeneracy of the two upper bands along Z-M for K-(ET)2l3. In k-(ET)2Cu(NCS)2, due to the lack of a center of... 

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... 

Nonself-consistent Extended Hiickel—Tight-binding Method... 

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. 

In order to obtain a better model for the molecular bond, [Santos et al., 2006] employed the extended Hiickel, or tight binding, theory. For the breaking of the bond in a diatomic molecule according to the schemes... 

The band structure of a three-dimensional solid, such as a semiconductor crystal, can be obtained in a similar fashion to that of a polyene. Localized molecular orbitals are constructed based on an appropriate set of valence atomic orbitals, and the effects of delocalization are then incorporated into the molecnlar orbital as the number of repeat units in the crystal lattice is increased to infinity. This process is widely known to the chemical conununity as extended Hiickel theory (see Extended Hiickel Molecular Orbital Theory). It is also called tight binding theory by physicists who apply these methods to calcnlate the band structures of semiconducting and metallic solids. 

The calculation of the exact band structure from first principles, however, is rather complex and requires considerable simplifications. The usual and very successful method to calculate the band structure of organic charge transfer salts is a tight-binding method, called extended Hiickel approximation. In this approximation, one starts from the molecular orbitals (MO) which are approximated by linear combinations of the constituent atomic orbitals. Each MO can be occupied by two electrons with antiparallel spins. These valence electrons are assumed to be spread over the whole molecule. Usually, only the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are relevant and are, therefore, considered in most band-structure calculations [41]. 

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