| 1. |
- Galler, Anna, et al.
(author)
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Towards ab initio Calculations with the Dynamical Vertex Approximation
- 2018
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In: Journal of the Physical Society of Japan. - : PHYSICAL SOC JAPAN. - 0031-9015 .- 1347-4073. ; 87:4
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Journal article (peer-reviewed)abstract
- While key effects of the many-body problem-such as Kondo and Mott physics-can be understood in terms of onsite correlations, non-local fluctuations of charge, spin, and pairing amplitudes are at the heart of the most fascinating and unresolved phenomena in condensed matter physics. Here, we review recent progress in diagrammatic extensions to dynamical mean-field theory for ab initio materials calculations. We first recapitulate the quantum field theoretical background behind the two-particle vertex. Next we discuss latest algorithmic advances in quantum Monte Carlo simulations for calculating such two-particle quantities using worm sampling and vertex asymptotics, before giving an introduction to the ab initio dynamical vertex approximation (AbinitioDGA). Finally, we highlight the potential of AbinitioDGA by detailing results for the prototypical correlated metal SrVO3.
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| 2. |
- Edwards, Marten O. M., et al.
(author)
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Increased photoelectron transmission in High-pressure photoelectron spectrometers using "swift acceleration"
- 2015
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 785, s. 191-196
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Journal article (peer-reviewed)abstract
- A new operation mode of a HPXPS (high-pressure X-ray photoelectron spectroscopy) analyzer is evaluated on a HPXPS system fitted with an Al K alpha X-ray source. A variety of metal foil samples (gold, silver and copper) were measured in different sample gas environments (N-2 and H2O), and a front aperture diameter of 0.8 mm. The new design concept is based upon "swiftly" accelerating the photoelectrons to kinetic energies of several keV after they pass the analyzer front aperture. Compared to the standard mode, in which the front section between the two first apertures is field-free, this gives a wider angular collection and a lower tendency for electron losses in collisions with gas molecules within the analyzer. With the swift-acceleration mode we attain, depending on the experimental conditions, up to about 3 times higher peak intensities in vacuum and about 10 to 20 times higher peak intensities in the 6-9 mbar regime, depending on kinetic energy. These experimental findings agree well with simulated transmission functions for the analyzer. The new mode of operation enables faster data acquisition than the standard mode of operation, particularly valuable in a home laboratory environment. Further demonstrations of performance are highlighted by measurements of the valence band structure in dye sensitized solar cell photoelectrodes under a 2 mbar H2O atmosphere, a molecularly modified surface of interest in photoelectrochemical devices.
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| 3. |
- Eklund, Patrik, 1958-, et al.
(author)
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Hierarchical Wiring in Multigrids
- 1990
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In: CONPAR 90 — VAPP IV. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540530657 - 9783540465973 ; , s. 423-434
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Conference paper (peer-reviewed)
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| 4. |
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| 5. |
- Fischer, Hubertus, et al.
(author)
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Reconstruction of millennial changes in dust emission, transport and regional sea ice coverage using the deep EPICA ice cores from the Atlantic and Indian Ocean sector of Antarctica
- 2007
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In: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X. ; 260, s. 340-354
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Journal article (peer-reviewed)abstract
- Continuous sea salt and mineral dust aerosol records have been studied on the two EPICA (European Project for Ice Coring inAntarctica) deep ice cores. The joint use of these records from opposite sides of the East Antarctic plateau allows for an estimate ofchanges in dust transport and emission intensity as well as for the identification of regional differences in the sea salt aerosolsource. The mineral dust flux records at both sites show a strong coherency over the last 150 kyr related to dust emission changes inthe glacial Patagonian dust source with three times higher dust fluxes in the Atlantic compared to the Indian Ocean sector of theSouthern Ocean (SO). Using a simple conceptual transport model this indicates that transport can explain only 40% of theatmospheric dust concentration changes in Antarctica, while factor 5–10 changes occurred. Accordingly, the main cause for the strong glacial dust flux changes in Antarctica must lie in environmental changes in Patagonia. Dust emissions, hence environmentalconditions in Patagonia, were very similar during the last two glacials and interglacials, respectively, despite 2–4 °C warmertemperatures recorded in Antarctica during the penultimate interglacial than today. 2–3 times higher sea salt fluxes found in bothice cores in the glacial compared to the Holocene are difficult to reconcile with a largely unchanged transport intensity and thedistant open ocean source. The substantial glacial enhancements in sea salt aerosol fluxes can be readily explained assuming sea iceformation as the main sea salt aerosol source with a significantly larger expansion of (summer) sea ice in the Weddell Sea than inthe Indian Ocean sector. During the penultimate interglacial, our sea salt records point to a 50% reduction of winter sea icecoverage compared to the Holocene both in the Indian and Atlantic Ocean sector of the SO. However, from 20 to 80 ka beforepresent sea salt fluxes show only very subdued millennial changes despite pronounced temperature fluctuations, likely due to thelarge distance of the sea ice salt source to our drill sites.
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| 6. |
- Galler, Anna, et al.
(author)
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The AbinitioD Gamma A Project v1.0 : Non-local correlations beyond and susceptibilities within dynamical mean-field theory
- 2019
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In: Computer Physics Communications. - : ELSEVIER. - 0010-4655 .- 1879-2944. ; 245
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Journal article (peer-reviewed)abstract
- The ab initio extension of the dynamical vertex approximation (D Gamma A) method allows for realistic materials calculations that include non-local correlations beyond GW and dynamical mean-field theory. Here, we discuss the AbinitioD Gamma A algorithm, its implementation and usage in detail, and make the program package available to the scientific community.Program summary: Program Title: AbinitioD Gamma A Program Files: doi: http : //dx doi org/10 17632/h3k3f g6szb. 1 Licensing provisions: GNU General Public License v3 Programming language: Fortran95 and Python Required dependencies: MPI, LAPACK, BLAS, HDF5 (>= 1.8.12), Python (> 2.7), h5py (>= 2.5.0), numpy (>= 1.9.1) Optional dependencies: pip, matplotlib (>= 1.5.1), scipy (>= 0.14.0) Supplementary material: Test case files and step-by-step instructions. Nature of problem: Realistic materials calculations including non-local correlations beyond dynamical mean-field theory (DMFT) as well as non-local interactions. Solving the Bethe-Salpeter equation for multiple orbitals. Determining momentum-resolved susceptibilities in DMFT.Solution method: Ab initio dynamical vertex approximation: starting from the local two-particle vertex and constructing from it the local DMFT correlations, the GW diagrams, and further non-local correlations, e.g., spin fluctuations. Efficient solution of the Bethe-Salpeter equation, avoiding divergencies in the irreducible vertex in the particle-hole channel by reformulating the problem in terms of the full vertex. Parallelization with respect to the bosonic frequency and transferred momentum. Additional comments including restrictions and unusual features: As input, a Hamiltonian derived, e.g., from density functional theory and a DM Gamma T solution thereof is needed including a local two-particle vertex calculated at DMFT self-consistency. Hitherto the AbinitioD Gamma A program package is restricted to SU(2) symmetric problems. A so-called lambda correction or self-consistency is not yet implemented in the AbinitioD Gamma A code. Susceptibilities are so far only calculated within DM Gamma T, not the dynamical vertex approximation.
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| 7. |
- Kaufmann, Patrik, et al.
(author)
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Ammonium and non-sea salt sulfate in the EPICA ice cores as indicator of biological activity in the Southern Ocean
- 2010
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:02-jan, s. 313-323
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Journal article (peer-reviewed)abstract
- Sulfate (SO42-) and ammonium (NH4+) flux records over the last 150,000 years from both Antarctic EPICA ice cores (European Project for Ice Coring in Antarctica) are presented. The ice core record from Dome C is influenced by the Indian sector of the Southern Ocean (SO), whereas Dronning Maud Land is facing the Atlantic sector. Generally, they reflect the past atmospheric aerosol load and, thus, potentially reveal the fingerprint of marine biogenic sources from the SO. The most important feature of both, the nssSO(4)(2-) as well as NH4+ flux records, is the absence of any significant glacial cycles, in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150,000 years. This finding challenges the iron fertilization hypothesis on long time scales, as the significant changes in dust, e.g. from the last glacial maximum toward the Holocene have neither an impact on nssSO(4)(2-) nor on NH4+ fluxes found in interior Antarctica. The inter-site correlation of both species is weak, r(2) = 0.42 for the nssSO(4)(2-) flux and r(2) = 0.12 for the NH4+ flux respectively, emphasizing the local Source characteristics of biogenic aerosol from the SO. Millennial variability in NH4+ and nssSO(4)(2-) is within the uncertainty of our flux estimates. Correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssSO(4)(2-) flux for the Atlantic sector of the Southern Ocean, but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at EDML.
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| 8. |
- Wilhelms, Frank, et al.
(author)
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The EPICA Dronning Maud Land deep drilling operation
- 2014
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In: Annals of Glaciology. - 0260-3055 .- 1727-5644. ; 55:68, s. 355-366
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Journal article (peer-reviewed)abstract
- We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. corebreak force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run.
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