5,466 research outputs found

    Density functional perturbation theory within non-collinear magnetism

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    We extend the density functional perturbation theory formalism to the case of non-collinear magnetism. The main problem comes with the exchange-correlation (XC) potential derivatives, which are the only ones that are affected by the non-collinearity of the system. Most of the present XC functionals are constructed at the collinear level, such that the off-diagonal (containing magnetization densities along xx and yy directions) derivatives cannot be calculated simply in the non-collinear framework. To solve this problem, we consider here possibilities to transform the non-collinear XC derivatives to a local collinear basis, where the zz axis is aligned with the local magnetization at each point. The two methods we explore are i) expanding the spin rotation matrix as a Taylor series, ii) evaluating explicitly the XC for the local density approximation through an analytical expression of the expansion terms. We compare the two methods and describe their practical implementation. We show their application for atomic displacement and electric field perturbations at the second order, within the norm-conserving pseudopotential methods

    Intranasal corticosteroids in allergic rhinitis in COVID-19 infected patients: An ARIA-EAACI statement

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    A novel strain of human coronaviruses, named by the International Committee on Taxonomy of Viruses (ICTV)1 as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has emerged and caused an infectious disease. This disease has recently been referred to by the World Health Organisation (WHO) as the “coronavirus disease 2019” (COVID-19). Since the first report of this disease in December 2019 in Wuhan, China,2, 3 COVID-19 has aggressively spread across the globe. WHO declared it a pandemic on March 11

    Combinatorics of Hard Particles on Planar Graphs

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    We revisit the problem of hard particles on planar random tetravalent graphs in view of recent combinatorial techniques relating planar diagrams to decorated trees. We show how to recover the two-matrix model solution to this problem in this purely combinatorial language.Comment: 35 pages, 20 figures, tex, harvmac, eps

    Conclusion

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    The PseudoDojo: Training and grading a 85 element optimized norm-conserving pseudopotential table

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    First-principles calculations in crystalline structures are often performed with a planewave basis set. To make the number of basis functions tractable two approximations are usually introduced: core electrons are frozen and the diverging Coulomb potential near the nucleus is replaced by a smoother expression. The norm-conserving pseudopotential was the first successful method to apply these approximations in a fully ab initio way. Later on, more efficient and more exact approaches were developed based on the ultrasoft and the projector augmented wave formalisms. These formalisms are however more complex and developing new features in these frameworks is usually more difficult than in the norm-conserving framework. Most of the existing tables of norm- conserving pseudopotentials, generated long ago, do not include the latest developments, are not systematically tested or are not designed primarily for high accuracy. In this paper, we present our PseudoDojo framework for developing and testing full tables of pseudopotentials, and demonstrate it with a new table generated with the ONCVPSP approach. The PseudoDojo is an open source project, building on the AbiPy package, for developing and systematically testing pseudopotentials. At present it contains 7 different batteries of tests executed with ABINIT, which are performed as a function of the energy cutoff. The results of these tests are then used to provide hints for the energy cutoff for actual production calculations. Our final set contains 141 pseudopotentials split into a standard and a stringent accuracy table. In total around 70.000 calculations were performed to test the pseudopotentials. The process of developing the final table led to new insights into the effects of both the core-valence partitioning and the non-linear core corrections on the stability, convergence, and transferability of norm-conserving pseudopotentials. ...Comment: abstract truncated, 17 pages, 25 figures, 8 table

    Becoming war: towards a martial empiricism

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    Under the banner of martial empiricism, we advance a distinctive set of theoretical and methodological commitments for the study of war. Previous efforts to wrestle with this most recalcitrant of phenomena have sought to ground research upon primary definitions or foundational ontologies of war. By contrast, we propose to embrace war’s incessant becoming, making its creativity, mutability, and polyvalence central to our enquiry. Leaving behind the interminable quest for its essence, we embrace war as mystery. We draw on a tradition of radical empiricism to devise a conceptual and contextual mode of enquiry that can follow the processes and operations of war wherever they lead us. Moving beyond the instrumental appropriations of strategic thought and the normative strictures typical of critical approaches, martial empiricism calls for an unbounded investigation into the emergent and generative character of war. Framing the accompanying special issue, we outline three domains around which to orient future research: mobilization, design, and encounter. Martial empiricism is no idle exercise in philosophical speculation. It is the promise of a research agenda apposite to the task of fully contending with the momentous possibilities and dangers of war in our time

    Series expansions of the percolation probability on the directed triangular lattice

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    We have derived long series expansions of the percolation probability for site, bond and site-bond percolation on the directed triangular lattice. For the bond problem we have extended the series from order 12 to 51 and for the site problem from order 12 to 35. For the site-bond problem, which has not been studied before, we have derived the series to order 32. Our estimates of the critical exponent β\beta are in full agreement with results for similar problems on the square lattice, confirming expectations of universality. For the critical probability and exponent we find in the site case: qc=0.4043528±0.0000010q_c = 0.4043528 \pm 0.0000010 and β=0.27645±0.00010\beta = 0.27645 \pm 0.00010; in the bond case: qc=0.52198±0.00001q_c = 0.52198\pm 0.00001 and β=0.2769±0.0010\beta = 0.2769\pm 0.0010; and in the site-bond case: qc=0.264173±0.000003q_c = 0.264173 \pm 0.000003 and β=0.2766±0.0003\beta = 0.2766 \pm 0.0003. In addition we have obtained accurate estimates for the critical amplitudes. In all cases we find that the leading correction to scaling term is analytic, i.e., the confluent exponent Δ=1\Delta = 1.Comment: 26 pages, LaTeX. To appear in J. Phys.

    Asymptotic behaviour of convex and column-convex lattice polygons with fixed area and varying perimeter

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    We study the inflated phase of two dimensional lattice polygons, both convex and column-convex, with fixed area A and variable perimeter, when a weight \mu^t \exp[- Jb] is associated to a polygon with perimeter t and b bends. The mean perimeter is calculated as a function of the fugacity \mu and the bending rigidity J. In the limit \mu -> 0, the mean perimeter has the asymptotic behaviour \avg{t}/4 \sqrt{A} \simeq 1 - K(J)/(\ln \mu)^2 + O (\mu/ \ln \mu) . The constant K(J) is found to be the same for both types of polygons, suggesting that self-avoiding polygons should also exhibit the same asymptotic behaviour.Comment: 10 pages, 3 figure
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