Theoretical investigations of the electronic structures

Several theoretical investigations have been performed on silicon-based clathrate structures. Whereas early publications discuss an insulator-to-metal transition in Na-doped Na cSii36 with electrons moving in a band with predominantly Na contributions, recent calculations predict a narrow conduction band and a distribution of the charge density over the Si atoms.  

There has been less interest in phases of the heavier homologs of the group-14 elements. There are indications that )5-NaSn, which contains tetrahedral S114 imits, is metallic and augmented spherical-wave calculations reveal a small indirect 

The LMTO-band structure also reveals the metallic character of the intermetallic phase K5Pb24. ° The Fermi level cuts at low DOS, but flat bands also occur at (Fig. 7c) showing up as a small shoulder in the DOS E-p consequently cuts the DOS at a local maximum. The ELF analyses show areas of high localization (ELF 0.8) close to the Pb atoms. The regions are located at the largest cone angle described by the connections to next-nearest neighbors of the respective Pb atom, e.g. 12 lone pairs are located around K2 inside the truncated tetrahedral unit, three 

EPR measurements show the existence of paramagnetic clusters, magnetic susceptibility data reveal magnetic moments indicative of fewer than one unpaired electron per cluster. Nine-atom 9 clusters also occur in binary phases, but tetrahedral four-atom 4 clusters are predominant beside the arachno-typs 5 clusters. 

Even though the first reports on this extraordinary class of cluster compounds were published more than a century ago, detailed measurements of the physical properties of compounds containing discrete or linked clusters have just begun. Further efforts to achieve a deeper understanding of the relationships between structure and properties in this field are certainly foreseen. 

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Cambridge) and J. H. van Vleck (Harvard) fundamental theoretical investigations of the electronic structure of magnetic and disordered systems. 

Recent work also has focused on theoretical investigations of the electronic structure and electronic transitions of Os(II) imine complexes. Baranovskii and Lyubimova have employed ab initio methods to obtain vibrational frequencies and distortions following excitation to determine rate constants for nonradiative transitions of complexes having MLCT excited states [29]. 

During electron transfer, the Cua site alternates between the fully reduced and the mixed-valence (Cu +Cu ) forms. Interestingly, the unpaired electron in the mixed-valence form seems to be delocalised between the two copper ions. Several theoretical investigations of the electronic structure and spectrum of the Cua dimer have been published [138-144]. In similarity to the blue copper proteins, it has been suggested that the structure and the properties of the Cua site is determined by protein strain. More precisely, it has been proposed [136] that Cua in its natural state is similar to an inorganic model studied by Tolman and coworkers [145]. This complex has a long Cu-Cu bond (293 pm) and short axial interactions (-212 pm). The protein is said to enforce weaker axial interactions, which is conpensated by shorter bonds to the other ligands and the formation of a Cu-Cu bond. This should allow the protein to modulate the reduction potential of the site [136,146]. 

A number of theoretical investigations of the electronic structures of small carbon-containing molecules have been undertaken.4-6 The relative... 

A theoretical investigation of the electronic structure of the normal and excited states of copper dimethylglyoxime and its adducts with water and amines. Acta Chem. Scand. 21, 1855. 

In a theoretical investigation of the electronic structure of diamond, its valence bands have been determined using a linear combination of bonding molecular orbitals formed from s—p hybridization of the 2s, 2p Hartree-Fock atomic orbitals of the isolated carbon atom. 

Methane. Altogether eight theoretical investigations of the electronic structure of ground, excited, and ionized states of methane have been carried out 1 ... 

Theoretical investigations of the electronic structures of CO, COS, and have been undertaken. The results of the analysis of the elec-... 

Nobel prize for Physics John Bardeen, Leon N. Cooper and J. Robert Schrieffer, for their jointly developed theory of superconductivity, usually called the BCS theory. 1977 Nobel prize for Physics Philip W. Anderson, Sir Nevill F. Mott and John H. van Vleck, for their fundamental theoretical investigations of the electronic structure of magnetic and disordered systems. 

The remarkable effects caused by vacancies on the properties of carbides and nitrides have given rise to numerous experimental and theoretical studies. In the present overview we will concentrate on theoretical approaches only, although experimental results are imperative as a basis for testing theoretical models and methods. A complete list of references of computations on nonstoichiometric carbides and nitrides can be found in the book of Gubanov et al. (7). An essential problem in the theoretical investigations of the electronic structure of the substoichio-metric materials is a proper description of the vacancy-containing phases. Various concepts and models have been devised to treat the vacancy problem. Essentially four different types of approaches can be distinguished. 

Three main tendencies have been underlined in recent studies of structure and action mechanism ofbacterial photosynthetic reaction centers. The crystallographic structure of the reaction centers from Rps. viridis and Rb. spheroids was initially determined to be 2.8 and 3 A resolutions (Michel and Deisenhofer et al., 1985 Allen et al., 1986). Resolution and refinement of these structures have been subsequently extended to 2.2, 2.3 and 2.6 A. (Rees et al., 1989 Stowell et al., 1997, Fyfe and Johns, 2000 Rutherford and Faller, 2001). Investigations of the electronic structure of donor and acceptor centers in the ground and exited states by modern physical methods with a combination ofpico-and femtosecond kinetic techniques have become more precise and elaborate. Extensive experimental and theoretical investigations on the role of orbital overlap and protein dynamics in the processes of electron and proton transfer have been done. All the above-mentioned research directions are accompanied by extensive use of methods of sit-directed mutagenesis and substitution of native pigments for artificial compounds of different redox potential. 

S. Linic, H. Piao, K. Adib, M. A. Barteau, Ethylene epoxidation on Ag Identification of the crucial surface intermediate by experimental and theoretical investigation of its electronic structure, Angew. Chem. Int. Ed. 43 (2004) 2918. 

Two theoretical analyses of the electronic structures of carbonates and related species have been published. - Russian workers have reported the results of MO calculations of the isoelectronic series of oxy-anions BO , CO ", and NOj. The derived data, when compared to the results of Jf-ray spectral investigations, accurately describe the principal characteristics of the spectra. Perkins has studied the electronic structure of inter alia H2CS3, CS ", and CS4 using a self-consistent MO method. Perhaps the most interesting conclusion to come from the investigations is the fact that the molecule H2CS3 is shown to be quite stable. 

In the quantum theory of matter the study of the physical properties of any system, an atom, a molecule, or a solid, begins with the determination of the energy levels and the wave functions of the many electrons in the system. For this reason the theoretical and experimental investigations of the electronic structure of rare-earth metals have always occupied an important position in rare earth research. The pioneering calculations of the energy band structure of rare earth metals were motivated by the attempt to understand the complicated magnetic structures of these metals as revealed by neutron scattering. These... 

Armelao L, Bettinelli M, Casarin M, Granozzi G, Tondello E, Vitladirri A (1995) A theoretical arrd experimental investigation of the electronic structure of a-Fe203 thin films J Phys Cond Mat 7 L299-L305... 

In Chapter 9, the vibrational spectra of linear polymers, including a description how one can obtain force constants and vibrational frequencies by calculating the total electronic energy at different bond distances, are discussed first. The theory is supplemented by methods for the treatment of vibrations in disordered polymers, which are very similar to those used in the investigation of the electronic structure in disordered chains (see Chapter 4). In several cases the theoretically computed and experimental vibrational spectra are compared. 

In this chapter we begin a systematic description of the electronic structure investigations of d-metal refractory compounds. As was mentioned in the Preface, this book is dedicated mainly to the analysis of results obtained by theoretical methods, and, therefore, both in this and subsequent chapters we use experimental data only when they are necessary for comparison with computational results. A considerable proportion of the papers dealing with the electronic structure calculations of binary phases describe results obtained simultaneously for carbides and nitrides. This chapter is limited to the description of the electronic structure of carbides only, necessary comparisons with nitrides being made in Chapter 3. The investigations of the electronic structure of nonstoichiometric refractory compounds are analysed in Chapter 4. 

Cubic nitrides have been the subject of many theoretical and experimental investigations. A list of references for the theoretical studies of the electronic structure of this group of compounds is given at the end of this chapter. 

The theoretical studies " have been focused on TiSi2. Some attempts, with use of high-symmetry crystal structures, have been made to understand some of the other titanium silicides. This paper deals vith Ti,5Si.3. Because of the crucial interplay between structure and bonding we have studied the proposed stable low-symmetry crystal structure. This will give a better picture of the electronic structure and the bonding properties in this system. An investigation of seven members in the Ti-Si system will be presented in a future publication. ... 

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