241 research outputs found
Correlation-enhanced electron-phonon coupling: Applications of GW and screened hybrid functional to bismuthates, chloronitrides, and other high Tc superconductors
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
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
PRM226 Don’t Make Me Wait: The Variance Reduction Technique for Faster Monte Carlo Simulations in Cost Effectiveness Models on Web
Chemical Weapon and Military-Historical Aspects of International Law
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
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Theoretical Study on the Compounds NpM2, PuM2, AmM2 (M = Mn, Fe, Ni,Co) and on the System Pu-U
The relativistic spin-polarized density functional theory has been used for the study of electronic and magnetic structure of the compounds NpM{sub 2}, PuM{sub 2} and AmM{sub 2} (M = Mn; Fe;Co;Ni). It has been shown that the peculiarities in their magnetic properties come mainly from the hybridization between 5f-electrons of actinides and 3d-electrons of transition metals. It is interesting, that existence of the local magnetic moments appears to be possible on the atoms, despite the fact that Hill's condition is not satisfied for these compounds of actinides. Besides, the electronic and magnetic structures of PuU have been studied and the comparative analysis of them with another compounds of plutonium and its neighbors in Periodic System: PuNp and PuAm has been performed. It has been found that in all the cases the electronic structure formation is a result of a superposition of spin-orbit and exchange band splitting with some increasing of the role of exchange as we are going to americium. Atoms of plutonium appear to be near the point of equal importance of both interactions
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Calculational Study on the Compounds Np3M, Am3M, and on the System Pu-Am
Spin-polarized relativistic density functional theory has been employed for the study of the electronic and magnetic structures for the compounds Np{sub 3}M and Am{sub 3}M (M = Al; Ga; In) and their comparison with plutonium's alloys Pu{sub 3}M has been made. It has been found that of the three actinides (Np, Pu, Am) only plutonium has its FCC structure essentially more stable after alloying with aforementioned elements. Apart from that, the electronic and magnetic structures for the system Pu-Am presented by three different compounds: Pu{sub 3}Am, PuAm, and PuAm{sub 3} have been investigated. Their magnetic structures have been found to be too robust in comparison with the experimental fact that magnetism in Pu-Am system depends strongly on the percentage of the americium in the alloy. One possible explanation consists in the overestimation of the spin splitting and in the disregarding of orbital dependence of the exchange-correlation potential
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Ab-Initio Study on Plutonium Compounds Pu3M (M=Al, Ga, In), PuNp and Elemental Neptunium
Using spin-polarized relativistic density functional theory the electronic and magnetic structures for the plutonium compounds Pu{sub 3}M(M = Al; Ga; In) and PuNp have been investigated. For the first group of compounds the enhanced hybridization between Pu 5f and p-states of alloying element, as it has been found in spin-polarized calculations, is believed to be the main reason for the higher formation energies obtained in such kind of studies in comparison with the non-spin-polarized case. Also, comparative analysis of the actinides U, Np, Pu, Am, and Cm has been performed based on their electronic and magnetic structure. Some noticeable difference in the calculated magnetic structure was discovered between the actinide with local magnetic moments (Cm) and the actinides (Pu, Am) in which magnetic moments were found only in the calculations
Spin-density fluctuations and the fluctuation-dissipation theorem in 3d ferromagnetic metals
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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