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In this communication we present together four distinct techniques for the study of electronic structure of solids: the tight-binding linear muffin-tin orbitals, the real space and augmented space recursions and the modified exchange-correlation. Using this we investigate the effect of random vacancies on the electronic properties of the carbon hexagonal allotrope, graphene, and the non-hexagonal allotrope, planar T graphene. We have inserted random vacancies at different concentrations, to simulate disorder in pristine graphene and planar T graphene sheets. The resulting disorder, both on-site (diagonal disorder) as well as in the hopping integrals (off-diagonal disorder), introduces sharp peaks in the vicinity of the Dirac point built up from localized states for both hexagonal and non-hexagonal structures. These peaks become resonances with increasing vacancy concentration. We find that in presence of vacancies, graphene-like linear dispersion appears in planar T graphene and the cross points form a loop in the first Brillouin zone similar to buckled T graphene that originates from $$\pi$$ and $$\pi$$ * bands without regular hexagonal symmetry. We also calculate the single-particle relaxation time, $$\tau (\vec {q})$$ of $$\vec {q}$$ labeled quantum electronic states which originates from scattering due to presence of vacancies, causing quantum level broadening. [ABSTRACT FROM AUTHOR]

The main aim of this work is to present two different methodologies for configuration averaging in disordered systems. The Recursion method is suitable for the calculation of spatial or self-averaging, while the augmented space formalism averages over different possible configurations of the system. We have applied these techniques to a simple example and compared their results. Based on these, we have reexamined the concept of spatial ergodicity in disordered systems. The specific aspect, we have focused on, is the question 'Why does an experimentalist often obtain the averaged result on a single sample?' We have found that in our example of disordered graphene, the two lead to the same result within the error limits of the two methods. [ABSTRACT FROM AUTHOR]

We study the effect of skeleton conformations on the electronic structure of polysilanes and polysilanes with 50% Ti substitution (polytitasilanes) using first principle calculations. Various conformations including a trans-planar and a helical geometry of the skeleton backbone are examined. We found that in all cases, as the skeleton backbone is twisted away from being trans-planar, the bandgap increases. The overall band structures also exhibit some differences between the planar and helical configurations. The density of states shows that as Ti atoms are incorporated into the silane systems, the frontier state narrows indicating that the Ti substitution plays a major role at the lowest unoccupied conduction band and the highest occupied valance band. In addition, the backbone conformation has a strong influence on the bandgap and the frontier state for polytitasilanes which is not as apparent in the polysilanes. [ABSTRACT FROM AUTHOR]

The structural, electronic, elastic and magnetic properties of gadolinium and its hydrides GdH x ( x =1, 2, 3) are investigated by using Vienna ab-initio simulation package with the generalized gradient approximation parameterized by Perdew, Burke and Ernzerhof (GGA-PBE) plus a Hubbard parameter (GGA-PBE+ U ) in order to include the strong Coulomb correlation between localized Gd 4f electrons. At ambient pressure all the hydrides are stable in the ferromagnetic state. The calculated lattice parameters are in good agreement with the experimental results. The bulk modulus is found to decrease with the increase in the hydrogen content for the gadolinium hydrides. A pressure-induced structural phase transition is predicted to occur from cubic to hexagonal phase in GdH and GdH 2 and from hexagonal to cubic phase in GdH 3 . The electronic structure reveals that mono and di-hydrides are metallic, whereas trihydride is half-metallic at normal pressure. On further increasing the pressure, a half-metallic to metallic transition is also observed in GdH 3 . The calculated magnetic moment values of GdH x ( x =1, 2, 3) are in accord with the experimental values. [ABSTRACT FROM AUTHOR]

The full potential-linearized augmented plane wave method has been used to calculate structural, electronic and transport properties of proposed '122' compounds namely SrNiBi and BaNiBi using first principle calculations. These compounds belong to ThCrSi-type tetragonal structure and are isostructural with SrNi(P/As) and BaNi(P/As) compounds. The lattice constants of SrNiBi and BaNiBi are derived from their respective parent compounds. Optimized lattice constant, energy band structure, electron density plots and superconducting transition temperature are computed for the parent compounds. The calculated results are in reasonable agreement with earlier experimental values and theoretical results. The proposed compounds show similar electronic and bonding characteristics of their respective parent low temperature superconductors. [ABSTRACT FROM AUTHOR]

The electronic structure and shape of the Fermi surface are known to be of fundamental importance for the superconducting instability in real materials. We demonstrate that such an instability may be explored by static Cooper pair susceptibility renormalized by pairing interaction and present an efficient method of its evaluation using Wannier orbitals derived from ab initio calculation. As an example, this approach is used to search for an unconventional superconducting phase of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) type in a heavy-fermion compound CeCoIn _5 and an iron-based superconductor FeSe. The results suggest that the FFLO superconducting phase occurs at finite magnetic field in both materials.

The models of the heterostructures based on the ß-InSe, In4Se3 and In4Te3 crystals were proposed and the first-principles study of their electronic and optical properties were presented. The band spectra, the spatial distributions of the electron density and the absorption coefficients for different polarizations along crystal axes for the heterostructures of the (In4Se3)_m/(In4Te3)m and ß-InSe/In4Se3 type were calculated. The evolution of the changes in both energy spectrum and optical functions of the heterostructures in comparison with the bulk crystals has been analyzed. Our calculations point out the heterostructures stability and good agreement with the experimental investigations of the photosensitivity in the near and middle infrared region. [ABSTRACT FROM AUTHOR]

We have carried out a theoretical investigation of the structural, electronic and optical properties of mercury chalcogenides under pressure via first-principle calculations within the density functional theory. The structural phase transition from zincblende (ZB) to rock salt phases is determined. The calculated band structure in ZB phase was compared with experimental and theoretical findings. Optical properties including the real and imaginary parts of the complex dielectric function and the frequency-dependent reflectivity are explained to characterize the optical nature of mercury chalcogenides in both phases. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel hybrid sp-sp2 monoclinic carbon allotrope mC12. This allotrope is a promising light metallic material, the mechanical and electronic properties of which are studied based on first-principles calculations. The structure of this new mC12 is mechanically and dynamically stable at ambient pressure and has a low equilibrium density due to its large cell volume. Furthermore, calculations of the elastic constants and moduli reveal that mC12 has a rigid mechanical property. Finally, it exhibits metallic characteristics, owing to the mixture of sp-sp2 hybrid carbon atoms. [ABSTRACT FROM AUTHOR]