241 research outputs found

    Correlation-enhanced electron-phonon coupling: Applications of GW and screened hybrid functional to bismuthates, chloronitrides, and other high Tc superconductors

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    We show that the electron-phonon coupling (EPC) in many materials can be significantly underestimated by the standard density functional theory (DFT) in the local density approximation (LDA) due to large non-local correlation effects. We present a simple yet efficient methodology to evaluate the realistic EPC going beyond LDA by using more advanced and accurate GW and screened hybrid functional DFT approaches. The corrections we propose explain the extraordinarily high superconducting temperatures that are observed in two distinct classes of compounds-the bismuthates and the transition metal chloronitrides, thus solving a thirty-year-old puzzle. Our work calls for the critically reevaluation of the EPC of certain phonon modes in many other materials such as cuprates and iron-based superconductors. The proposed methodology can be used to design new correlation-enhanced high temperature superconductors and other functional materials involving electron-phonon interaction.Comment: Substantilly extended version of the previous manuscript, 19 pages, 10 figures, accepted for publication in Phys. Rev.

    Self consistent GW determination of the interaction strength: application to the iron arsenide superconductors

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    We introduce a first principles approach to determine the strength of the electronic correlations based on the fully self consistent GW approximation. The approach provides a seamless interface with dynamical mean field theory, and gives good results for well studied correlated materials such as NiO. Applied to the recently discovered iron arsenide materials, it accounts for the noticeable correlation features observed in optics and photoemission while explaining the absence of visible satellites in X-ray absorption experiments and other high energy spectroscopies.Comment: 3 figs, 4 page

    Chemical Weapon and Military-Historical Aspects of International Law

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    All the history of mankind is accompanied with armed conflicts. But only within the last 150 years, proceeding from the reasons of humanity, the states have established the international norms limiting the ways of war conducting and protecting its victims. Such basic norms are Geneva and Hague conventions. The application of intoxication substances during the First world war became an event in the development of military art, not less important than the occurrence of fire-arms in Middle Ages. This hi-tech weapon became a harbinger of war conducting means in the XX century, known today as the weapon of mass defeat

    Spin-density fluctuations and the fluctuation-dissipation theorem in 3d ferromagnetic metals

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    Spatial and time scales of spin density fluctuations (SDF) were analyzed in 3d ferromagnets using ab initio linear response calculations of complete wavevector and energy dependence of the dynamic spin susceptibility tensor. We demonstrate that SDF are spread continuously over the entire Brillouin zone and while majority of them reside within the 3d bandwidth, a significant amount comes from much higher energies. A validity of the adiabatic approximation in spin dynamics is discussed. The SDF spectrum is shown to have two main constituents: a minor low-energy spin wave contribution and a much larger high-energy component from more localized excitations. Using the fluctuation-dissipation theorem (FDT), the on-site spin correlator (SC) and the related effective fluctuating moment were properly evaluated and their universal dependence on the 3d band population is further discussed
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