Tight-binding bands

M. C. Desjonqueres and D. Spanjaard, Concepts in Surface Physics, Second Edition, Springer Verlag, Berlin (1996) and references therein R. Haydock, V. Heine and M. J. Kelly, Electronic Structure Based on the Local Atomic Environment for Tight-Binding Bands,. Phys. C 5 2845 (1972)... 

Tight-binding band electronic structure calculations have been... 

In this section we show how the general form of Renner-Teller interaction matrices can be obtained at any order in the phonon variables and with electron orbital functions of different symmetry (p-like, < like, /-like, etc.). For this purpose, we use an intuitive approach [18] based on the Slater-Koster [19] technique and its generalization [20] to express crystal field or two-center integrals in terms of independent parameters in the tight-binding band theory [21] then we apply standard series developments in terms of normal coordinates. 

The aim of this article is to show that the new quasi-two-dimensional organic conductor p -(BEDO-TTF)5[CsHg(SCN)4]2 [hereafter called (BEDO)CsHg] (BEDO-TTF - bis-(ethylenedioxy)tetrathiafulvalene) which contains closed and open orbits displays rather complicated oscillatory spectra associated with magnetic breakdown (MB) and quantum interference (QI) effects. Tight binding band structure calculations for this compound are proposed to characterise its Fermi surface. The aim of the article includes also an investigation of the optical conductivity anisotropy with polarized infrared reflectance spectra. 

The tight-binding band structure calculations were based upon the effective one-electron Hamiltonian of the extended Huckel method. [5] The off-diagonal matrix elements of the Hamiltonian were calculated acording to the modified Wolfsberg-Helmholtz formula. All valence electrons were explicitly taken into account in the calculations and the basis set consisted of double- Slater-type orbitals for C, O and S and a single- Slater-type orbitals for H. The exponents, contraction coefficients and atomic parameters were taken from previous work [6],... 

The behaviour of the quantum oscillations in (BEDO-TTF)5[CsHg(SCN)4]2 seems to be in good agreement with the predictions of tight binding band structure calculations. The additional frequencies in the SdH oscillations spectrum are most probably caused by the quantum interference effect. Thus, we propose that Fig. 5 provides an adequate description of the Fermi surface of (BEDO-TTF)5[CsHg(SCN)4]2 and that the... 

Itinerant-electron magnetism is found in a narrow range of bandwidths AW near W C/eff-For broader bands, localized spins on the M atoms are suppressed, and the tight-binding band-... 

Many of these properties may be rationalized in terms of a unique multisheet Fermi surface based on both the HOMO and the LUMO bands (211, 221, 247) and not solely on the HOMO band as in organic superconductors (13). Tight-binding band calculations have shown that the nature of the conduction band depends on the degree of dimerization within the stacks. This band originates either from the LUMO for weakly dimerized systems, or from the HOMO for strongly dimerized systems (221). 

The most orthodox model involving a quasi-one-dimensional tight-binding band with electron scattering by acoustic phonons and molecular vibrations (one-phonon processes) has been analyzed carefully and in great detail [43,44]. Good agreement with experimental data is claimed by the proponents of this model. 

Figure 4.7. The LCAO (tight-binding) band structure for ReOs. The dashed line represents the Fermi energy. To the far right is the density-of-states (DOS) curve for states of one spin. The occupied states (up to the Fermi level) are shaded gray. Note that the valence band is completely filled while the conduction band is partially filled. Hence, ReOs should be metallic.

Figure 5.3. The tight-binding band structure for graphene. The electronic properties are well described by the irand tt bands, which intersect atthe point K, making graphene a semi-metal.

In the tight-binding band approximation the analogous result for the dispersion relation can be written as... 

Numerical tight-binding band-structure calculations result in the approximative dispersion relation which is valid in the neighborhood of the FS [43]... 

The calculated tight-binding band structure based on the 20 K lattice parameters is shown in Fig. 4.44. Compared to other organic metals, unusually complicated dispersion relations are found which consist of ID and 3D energy bands. Perpendicular to c two ID FS sheets denoted by FSl and FS2 exist. Within the approximation used the doubly degenerate FSl is ideally... 

Molecular conductors exhibit a variety of physical properties that can be systematically understood on the basis of simple and clear electronic structures. Recent advances in angle-dependent magnetoresistance studies on molecular conductors have revealed that the simple tight-binding band calculation is very useful (but not almighty) to describe the Fermi surface topology [1, 2]. The variety observed in electronic structures heavily depends on the packing... 

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