Examining electronic structure

Tn some situations such as examining electronic structure, it can be important to include a k point at the T point. 

The electronic structures of porous solids have been examined by X-ray photoelectron spectroscopy (XPS). However, the penetration depth of electrons is 1 nm at best and XPS cannot examine electronic structures of inner pore-walls. XPS has been often used for the determination of surface chemical structures such as surface functional groups in activated carbon. Ar etching leads to the depth profile of electronic structures. This depth profile is often effective to evidence the presence of nanoporosity. 

Many phenomena in solid-state physics can be understood by resort to energy band calculations. Conductivity trends, photoemission spectra, and optical properties can all be understood by examining the quantum states or energy bands of solids. In addition, electronic structure methods can be used to extract a wide variety of properties such as structural energies, mechanical properties and thennodynamic properties. 

For bulk structural detemiination (see chapter B 1.9). the main teclmique used has been x-ray diffraction (XRD). Several other teclmiques are also available for more specialized applications, including electron diffraction (ED) for thin film structures and gas-phase molecules neutron diffraction (ND) and nuclear magnetic resonance (NMR) for magnetic studies (see chapter B1.12 and chapter B1.13) x-ray absorption fine structure (XAFS) for local structures in small or unstable samples and other spectroscopies to examine local structures in molecules. Electron microscopy also plays an important role, primarily tlirough unaging (see chapter B1.17). 

With only 90 elements, one might assume that there could be only about 90 different substances possible, but everyday experience shows that there are millions of different substances, such as water, brick, wood, plastics, etc. Indeed, elements can combine with each other, and the complexity of these possible combinations gives rise to the myriad substances found naturally or produced artificially. These combinations of elemental atoms are called compounds. Since atoms of an element can combine with themselves or with those of other elements to form molecules, there is a wide diversity of possible combinations to make all of the known substances, naturally or synthetically. Therefore, atoms are the simplest chemical building blocks. However, to understand atoms, it is necessary to examine the structure of a typical atom or, in other words, to examine the building blocks of the atoms themselves. The building blocks of atoms are called electrons, protons, and neutrons (Figure 46.1). 

Dravid et al. examined anisotropy in the electronic structures of CNTs from the viewpoint of momentum-transfer resolved EELS, in addition to the conventional TEM observation of CNTs, cross-seetional TEM and precise analysis by TED [5]. Comparison of the EEL spectra of CNTs with those of graphite shows lower jc peak than that of graphite in the low-loss region (plasmon loss), as shown in Fig. 7(a). It indicates a loss of valence electrons and a change in band gap due to the curved nature of the graphitic sheets. 

In order to examine the electronic structures of CNT it is necessary to first define the classification of structural configurations of CNT. The configuration of a CNT is constructed by enrolling a graphite sheet as illustrated in Fig. 1. That is. 

The optimised interlayer distance of a concentric bilayered CNT by density-functional theory treatment was calculated to be 3.39 A [23] compared with the experimental value of 3.4 A [24]. Modification of the electronic structure (especially metallic state) due to the inner tube has been examined for two kinds of models of concentric bilayered CNT, (5, 5)-(10, 10) and (9, 0)-(18, 0), in the framework of the Huckel-type treatment [25]. The stacked layer patterns considered are illustrated in Fig. 8. It has been predicted that metallic property would not change within this stacking mode due to symmetry reason, which is almost similar to the case in the interlayer interaction of two graphene sheets [26]. Moreover, in the three-dimensional graphite, the interlayer distance of which is 3.35 A [27], there is only a slight overlapping (0.03-0.04 eV) of the HO and the LU bands at the Fermi level of a sheet of graphite plane [28,29],... 

Thus it seems that the electronic structure of the inner tube does not seriously affect that of the most outside tube in MWCNT. More detailed theoretical and experimental examination on MWCNT is obviously desirable for complete understanding of miscellaneous interlayer interaction. 

Silicon cluster reactions are an example of a newly emerging field of research which is very amenable to study with electronic structure methods. This exercise will examine the potential surface for silicon cation reacting with silane (SiH4). Such reactions are central to the growth of large silicon clusters, which occurs by sequential additions of -SiHj ... 

Part 2, Model Chemistries, provides an in-depth examination of the accuracy, scope of applicability and other characteristics and trade-offs of all of the major well-defined electronic structure models. It also gives some general recommendations for selecting the best model for investigating a particular problem. 

Examine the structure, atomic charges and electrostatic potential map of phenyl diazonium ion. Which atom(s) appears to carry most of the positive charge Is the electron distribution around this atom(s) uniform, or are some regions more electron rich and others more electron poor Draw appropriate resonance contributors. 

Examine the structures and atomic charges for the various conjugate bases. How do they differ What distinctive features, if any, characterize the most stable conjugate base Draw all of the resonance contributors needed to account for the electron distribution and geometry of the most stable conjugate base. 

Examine the geometry of the most stable radical. Is the bonding in the aromatic ring fuUy delocalized (compare to model alpha-tocopherol), or is it localized Also, examine the spin density surface of the most stable radical. Is the unpaired electron localized on the carbon (oxygen) where bond cleavage occurred, or is it delocalized Draw all of the resonance contributors necessary for a full description of the radical s geometry and electronic structure. 

Before dealing with electronic structures as such, it will be helpful to examine briefly the experimental evidence on which such structures are based (Section 6.1). In particular, we need to look at the phenomenon of atomic spectra, m... 

In this work we examine the low energy UV-visible absorption spectrum of the [Fe2 ft - S2) P o- 61148) )2] complex, Figure 1, whose synthesis, structure, and properties have recently been reported. The complex contains a [Fe — S — S - Fe] core and is a structural isomer of the 2-Fe [Fe — ill — 8)2 — Fe ferredoxin. The electronic structure of the disulfide complex is, however, unknown, and can be associated with either an antifer-romagnetically (AF) coupled [Fe d ) - - Fe d )] system, or with a... 

PEMFC)/direct methanol fuel cell (DMFC) cathode limit the available sites for reduction of molecular oxygen. Alternatively, at the anode of a PEMFC or DMFC, the oxidation of water is necessary to produce hydroxyl or oxygen species that participate in oxidation of strongly bound carbon monoxide species. Taylor and co-workers [Taylor et ah, 2007b] have recently reported on a systematic study that examined the potential dependence of water redox reactions over a series of different metal electrode surfaces. For comparison purposes, we will start with a brief discussion of electronic structure studies of water activity with consideration of UHV model systems. 

Thompson MA, Zemer MC (1991) A theoretical examination of the electronic structure and spectroscopy of the photosynthetic reaction center from Rhodopseudomonas viridis. J Am Chem Soc 113 8210-8215... 

Perhaps the most fruitful of these studies was the radiolysis of HCo(C0)4 in a Kr matrix (61,62). Free radicals detected in the irradiated material corresponded to processes of H-Co fission, electron capture, H-atom additions and clustering. Initial examination at 77 K or lower temperatures revealed the presence of two radicals, Co(C0)4 and HCo(C0)4 , having similar geometries (IV and V) and electronic structures. Both have practically all of the unpaired spin-density confined to nuclei located on the three-fold axis, in Co 3dz2, C 2s or H Is orbitals. Under certain conditions, a radical product of hydrogen-atom addition, H2Co(C0)3, was observed this species is believed to have a distorted trigonal bipyramidal structure in which the H-atoms occupy apical positions. 

Our understanding of the physicochemical properties of pyrazines has deepened. The internal rotation and IR spectrum of 2,5-pyrazinedicarboxamide were studied by quantum chemical calculations <05TC73>, and ab initio MO calculations at the MP2/6-31++G( ) level were used to explain the electronic and vibrational properties of complexes of pyrazine and HX linear acids <05JMS2822>. MM and MO calculations were used to investigate the conformational and electronic properties of odor-active pyrazines <05JMS169>, and NMR, IR, X-ray, and DFT methods were used to examine the structures of pyridol l,2-a pyrazinium bromide <05JMS7>. 

It is well-established that the molecular and electronic structures of metal complexes of azamacrocycles are greatly affected upon N-alkylation (197). This is mainly due to two factors (a) the decrease of the ligand field strength and (b) the increase in the steric requirements upon going from a secondary to a tertiary amine donor function (251). To examine whether the properties of the dinuclear amine-thiophenolate complexes are affected by the N-alkyl substituents, analogous complexes of the... 

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