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Unknown quantum electronic conductance across nanojunctions made of silicon-doped carbon wires between carbon leads is investigated. This is done by an appropriate generalization of the phase field matching theory for the multi-scattering processes of electronic excitations at the nanojunction and the use of the tight-binding method. Our calculations of the electronic band structures for carbon, silicon, and diatomic silicon carbide are matched with the available corresponding density functional theory results to optimize the required tight-binding parameters. Silicon and carbon atoms are treated on the same footing by characterizing each with their corresponding orbitals. Several types of nanojunctions are analyzed to sample their behavior under different atomic configurations. We calculate for each nanojunction the individual contributions to the quantum conductance for the propagating σ, Π, and σ∗electron incidents from the carbon leads. The calculated results show a number of remarkable features, which include the influence of the ordered periodic configurations of silicon-carbon pairs and the suppression of quantum conductance due to minimum substitutional disorder and artificially organized symmetry on these nanojunctions. Our results also demonstrate that the phase field matching theory is an efficient tool to treat the quantum conductance of complex molecular nanojunctions.

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The structural, electronic properties and ionicity of the lithium ammonium sulfate dielectric crystals are examined using a complex approach including experimental studies of X-ray spectroscopy and the first principles band structure techniques within a framework of local electron density functional theory (DFT). Band energy dispersion, density of electronic states and dielectric function dispersion in the wide spectral range corresponding to electronic excitations were calculated using the plane wave basis and Vanderbilt ultra-soft pseudopotentials. The origin of the energy bands are estimated using density of states diagrams and the band gap magnitudes for different exchange correlation functions. To verify the data of the performed band structure calculations, the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) are used. The XPS core-level and valence-band spectra as well as the XES bands representing the energy distribution of the O 2p and N 2p states are studied. Theoretical refractive indices dispersion for the main crystallographic directions (n a , n b and n c ) as well as birefringence spectral dependences (Dn a , Dn b and Dn c ) in the visible spectral range are obtained. All the calculated properties are compared with the available experimental results and good agreement between both sets of data is demonstrated. a Institute of Physics, J. Dlugosz Academy, Armii Krajowej 13/15, PL-42-201,