Metal, electronic structure

The goal of many biomolecular NMR studies is characterization of global molecular structure. In metallo-biomolecules, and in particular, for paramagnetic species, it is sometimes preferable to use NMR to perform a more focused study of the metal ion coordination enviroiunent and the metal electronic structure. Metal sites show great variation in the effects on chemical shifts and line widths and thus often call for tailored approaches. In this section, characteristics of some of the metalloproteins metal sites most frequently studied by NMR are summarized. Examples have been selected to illustrate approaches described in this chapter such as metal substitution, use of pseudocontact shifts, RDCs, relaxation enhancement, and detection of nuclei other than H. 

Luce T A and Bennemann K H 1998 Nonlinear optical response of noble metals determined from first-principles electronic structures and wave functions calculation of transition matrix elements P/rys. Rev. B 58 15 821-6... 

Concelcao J, Laaksonen R T, Wang L S, Guo T, Nordlander P and Smalley R E 1995 Photoelectron spectroscopy of transition metal clusters correlation of valence electronic structure to reactivity Rhys. Rev. B 51 4668... 

Behm J M and Morse M D 1994 Spectroscopy of]et-cooled AIMn and trends in the electronic structure of the 3d transition metal aluminides J. Chem. Rhys. 101 6500... 

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The conduction of heat by liquid metals is directly related to tire electronic structure. Heat is caiTied tlrrough a metal by energetic electrons having... 

Al tshuler, L.V. and Bakanova, A.A., Electronic Structure and Compressibility of Metals at High Pressures, Soviet Phys. Uspekhi 11 (5), 678-689 (1969). 

J Li, L Noodleman, DA Case. Electronic structure calculations Density functional methods with applications to transition metal complexes. In EIS Lever, ABP Lever, eds. Inorganic Electronic Structure and Spectroscopy, Vol. 1. Methodology. New York Wiley, 1999, pp 661-724. 

Among the alkali metals, Li, Na, K, Rb, and Cs and their alloys have been used as exohedral dopants for Cgo [25, 26], with one electron typically transferred per alkali metal dopant. Although the metal atom diffusion rates appear to be considerably lower, some success has also been achieved with the intercalation of alkaline earth dopants, such as Ca, Sr, and Ba [27, 28, 29], where two electrons per metal atom M are transferred to the Cgo molecules for low concentrations of metal atoms, and less than two electrons per alkaline earth ion for high metal atom concentrations. Since the alkaline earth ions are smaller than the corresponding alkali metals in the same row of the periodic table, the crystal structures formed with alkaline earth doping are often different from those for the alkali metal dopants. Except for the alkali metal and alkaline earth intercalation compounds, few intercalation compounds have been investigated for their physical properties. 

As the nanotube diameter increases, more wave vectors become allowed for the circumferential direction, the nanotubes become more two-dimensional and the semiconducting band gap disappears, as is illustrated in Fig. 19 which shows the semiconducting band gap to be proportional to the reciprocal diameter l/dt. At a nanotube diameter of dt 3 nm (Fig. 19), the bandgap becomes comparable to thermal energies at room temperature, showing that small diameter nanotubes are needed to observe these quantum effects. Calculation of the electronic structure for two concentric nanotubes shows that pairs of concentric metal-semiconductor or semiconductor-metal nanotubes are stable [178]. 

Since the initial discovery[1,2] and subsequent development of large-scale synthesis of buckytubes[3], various methods for their synthesis, characterization, and potential applications have been pursued[4-12). Parallel to these experimental efforts, theoreticians have predicted that buckytubes may exhibit a variation in their electronic structure ranging from metallic to semiconducting, depending on the diameter of the tubes and the degree of helical arrangement[13-16]. Thus, careful characterization of buckytubes and their derivatives is essential for understanding the electronic properties of buckytubes. 

Studies on the electronic structure of carbon nanotube (CNT) is of much importance toward its efficient utilisation in electronic devices. It is well known that the early prediction of its peculiar electronic structure [1-3] right after the lijima s observation of multi-walled CNT (MWCNT) [4] seems to have actually triggered the subsequent and explosive series of experimental researches of CNT. In that prediction, alternative appearance of metallic and semiconductive nature in CNT depending on the combination of diameter and pitch or, more specifically, chiral vector of CNT expressed by two kinds of non-negative integers (a, b) as described later (see Fig. 1). 

In this chapter the results of detailed research on the realistic electronic structure of single-walled CNT (SWCNT) are summarised with explicit consideration of carbon-carbon bond-alternation patterns accompanied by the metal-insulator transition inherent in low-dimensional materials including CNT. Moreover, recent selective topics of electronic structures of CNT are also described. Throughout this chapter the terminology "CNT stands for SWCNT unless specially noted. 

Right after the discovery of MWCNT [4] several reports on the electronic structures of CNT were almost immediately reported based on rather simple tight-binding method or its equivalent [1-3,5,6]. The most interesting and important features therein [1-3] were that CNT will become either metallic or semiconductive depending on the configuration of CNT, that is. 

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