“Building Resilience” A comparison of eight OECD countries. Bertelsmann Stiftung Inclusive Growth for Germany|12

Increasing resilience is one of the top priorities of global economic policy. In a comparison of eight industrialized countries, a quite varied picture emerges. On four dimensions of performance (growth, unemployment, protection against poverty and distribution), Japan and Australia show considerable resilience in the context of crisis. France and Italy demonstrate a low level of resilience. The United States does little to serve as a role model for Europe with regard to resilience; while growth rates have been successfully stabilized there, crises have been accompanied by increases in inequality. The figure examines Germany’s performance in the context of crisis. Performance is measured using a preand post-crisis comparison. In comparison to the average of the here considered countries, Germany has coped with crises well with regard to consequences for distribution and unemployment. The consequences of a crisis with regard to poverty risks correspond with the country- sample average. In past decades, Germany has performed somewhat below the average level with regard to stabilizing growth. However, this improved significantly with the financial crisis

Electronic phase transitions of bismuth under strain from relativistic self-consistent GW calculations

We present quasiparticle self-consistent GW (QSGW) calculations of semimetallic bulk Bi. We go beyond the conventional QSGW method by including the spin-orbit coupling throughout the self-consistency cycle. This approach improves the description of the electron and the hole pockets considerably with respect to standard density functional theory (DFT), leading to excellent agreement with experiment. We employ this relativistic QSGW approach to conduct a study of the semimetal-to-semiconductor and the trivial-to-topological transitions that Bi experiences under strain. DFT predicts that an unphysically large strain is needed for such transitions. We show, by means of the relativistic QSGW description of the electronic structure, that an in-plane tensile strain of only 0.3% and a compressive strain of 0.4% are sufficient to cause the semimetal-to-semiconductor and the trivial-to-topological phase transitions, respectively. Thus, the required strain moves into a regime that is likely to be realizable in experiment, which opens up the possibility to explore bulklike topological behavior of pure Bi

Strength of the Effective Coulomb Interaction at Metal and Insulator Surfaces

The effective on-site Coulomb interaction (Hubbard $U$) between localized electrons at crystal surfaces is expected to be enhanced due to the reduced coordination number and reduced subsequent screening. By means of first principles calculations employing the constrained random-phase approximation (cRPA) we show that this is indeed the case for simple metals and insulators but not necessarily for transition metals and insulators that exhibit pronounced surface states. In the latter case, the screening contribution from surface states as well as the influence of the band narrowing increases the electron polarization to such an extent as to overcompensate the decrease resulting from the reduced effective screening volume. The Hubbard $U$ parameter is thus substantially reduced in some cases, e.g., by around 30% for the (100) surface of bcc Cr.Comment: 4.4 pages, 3 figures, 1 tabl

Efficient calculation of the Coulomb matrix and its expansion around k=0 within the FLAPW method

We derive formulas for the Coulomb matrix within the full-potential linearized augmented-plane-wave (FLAPW) method. The Coulomb matrix is a central ingredient in implementations of many-body perturbation theory, such as the Hartree-Fock and GW approximations for the electronic self-energy or the random-phase approximation for the dielectric function. It is represented in the mixed product basis, which combines numerical muffin-tin functions and interstitial plane waves that are here expanded with the Rayleigh formula. The resulting algorithm is very efficient in terms of both computational cost and accuracy and is superior to an implementation with the Fourier transform of the step function. In order to allow an analytic treatment of the divergence at k=0 in reciprocal space, we expand the Coulomb matrix analytically around this point without resorting to a projection onto plane waves. We then apply a basis transformation that diagonalizes the Coulomb matrix and confines the divergence to a single eigenvalue. At the same time, response matrices like the dielectric function separate into head, wings, and body with the same mathematical properties as in a plane-wave basis. As an illustration we apply the formulas to electron-energy-loss spectra for nickel at different k vectors including k=0. The convergence of the spectra towards the result at k=0 is clearly seen. Our treatment also allows to include transitions from core states that give rise to a shallow peak at high energies and lead to good agreement with experiment.Comment: 18 pages, 3 figure

Economic Resilience A new concept for policy making? Bertelsmann Stiftung Inclusive Growth for Germany|11

The idea of “resilience” has in recent years gained a high level of popularity in the formulation of economic- policy objectives. Given the rapid sequence of serious crises, the rise of this concept is hardly surprising. If economic shocks are apparently unavoidable, then an economy’s ability to cope with them should be a subject of interest. However, the virtually inflationary use of the resilience concept has been accompanied by a lack of precision. In particular, there is often no clear understanding that alongside its static interpretation (retention of a system’s existing functions in the case of a crisis), crisis resilience also includes an adaptive dimension (adjustment to new surrounding conditions). Against this background, this article addresses the origin of the resilience concept, illustrates its various usages in different disciplines, and distinguishes it from other key words (“vulnerability,” “sustainability,” “stability”). On this basis, the resilience concept is given additional precision and defined in a manner useful for the economic- policy perspective. A central conclusion is that the concept of resilience can become a normative economic- policy principle if 1) it is not viewed narrowly as only a static concept; 2) it is linked to the societal objectives within the economy being studied; and 3) the interplay of different societal levels is taken into account

Local exact exchange potentials within the all-electron FLAPW method and a comparison with pseudopotential results

We present a general numerical approach to construct local Kohn-Sham potentials from orbital-dependent functionals within the all-electron full-potential linearized augmented-plane-wave (FLAPW) method, in which core and valence electrons are treated on an equal footing. As a practical example, we present a treatment of the orbital-dependent exact-exchange (EXX) energy and potential. A formulation in terms of a mixed product basis, which is constructed from products of LAPW basis functions, enables a solution of the optimized-effective-potential (OEP) equation with standard numerical algebraic tools and without shape approximations for the resulting potential. We find that the mixed product and LAPW basis sets must be properly balanced to obtain smooth and converged EXX potentials without spurious oscillations. The construction and convergence of the exchange potential is analyzed in detail for diamond. Our all-electron results for C, Si, SiC, Ge, GaAs semiconductors as well as Ne and Ar noble-gas solids are in very favorable agreement with plane-wave pseudopotential calculations. This confirms the adequacy of the pseudopotential approximation in the context of the EXX-OEP formalism and clarifies a previous contradiction between FLAPW and pseudopotential results.Comment: 12 pages, 7 figures, 5 table

Raman cross section of spin ladders

We demonstrate that a two-triplet resonance strongly renormalizes the Raman spectrum of two-leg spin ladders and moreover suggest this to be the origin of the asymmetry of the magnetic Raman continuum observed in CaV2O5.Comment: 2 pages, 1 figur