Suchergebnisse

Density functional theory (DFT) has become a standard tool for ab-initio simulations for a wide range of applications. While the intrinsic cubic scaling of DFT was for a long time limiting the accessible system size to some hundred atoms, the recent progress with respect to linear scaling DFT methods has allowed to tackle problems that are larger by many orders of magnitudes. However, as these linear scaling methods were developed for insulators, they cannot, in general, be straightforwardly applied to metals, as a finite (electronic) temperature is needed to ensure locality of the density matrix. In this paper we show that, once finite electronic temperature is employed, the linear scaling version of the BigDFT code is able to exploit this locality to provide a computational treatment that scales linearly with respect to the number of atoms of a metallic system. We provide prototype examples based on bulk Tungsten, which plays a key role in finding safe and long-lasting materials for Fusion Reactors; however we do not expect any major obstacles in extending this work to cover other metals. We believe that such an approach might help in opening the path towards novel approaches for investigating the electronic structure of such materials, in particular when large supercells are required. ; We acknowledge valuable discussions with María José Caturla and Chu-Chun Fu. S.M. acknowledges support from the MaX project, which has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant agreements 676598. M.A. acknowledges support from the Novartis Universität Basel Excellence Scholarship for Life Sciences and the Swiss National Science Foundation (P300P2-158407, P300P2-174475). We gratefully acknowledge the computing resources on Marconi-Fusion under the EUROfusion project BigDFT4F, from the Swiss National Supercomputing Center in Lugano (project s700), the Extreme Science and Engineering Discovery Environment (XSEDE) (which is supported by National Science Foundation grant number OCI-1053575), the Bridges system at the Pittsburgh Supercomputing Center (PSC) (which is supported by NSF award number ACI-1445606), the Quest high performance computing facility at Northwestern University, and the National Energy Research Scientific Computing Center (DOE: DE-AC02- 05CH11231). ; Peer Reviewed ; Postprint (published version)

Density functional theory (DFT) has become a standard tool for ab-initio simulations for a wide range of applications. While the intrinsic cubic scaling of DFT was for a long time limiting the accessible system size to some hundred atoms, the recent progress with respect to linear scaling DFT methods has allowed to tackle problems that are larger by many orders of magnitudes. However, as these linear scaling methods were developed for insulators, they cannot, in general, be straightforwardly applied to metals, as a finite (electronic) temperature is needed to ensure locality of the density matrix. In this paper we show that, once finite electronic temperature is employed, the linear scaling version of the BigDFT code is able to exploit this locality to provide a computational treatment that scales linearly with respect to the number of atoms of a metallic system. We provide prototype examples based on bulk Tungsten, which plays a key role in finding safe and long-lasting materials for Fusion Reactors; however we do not expect any major obstacles in extending this work to cover other metals. We believe that such an approach might help in opening the path towards novel approaches for investigating the electronic structure of such materials, in particular when large supercells are required. ; We acknowledge valuable discussions with María José Caturla and Chu-Chun Fu. S.M. acknowledges support from the MaX project, which has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant agreements 676598. M.A. acknowledges support from the Novartis Universität Basel Excellence Scholarship for Life Sciences and the Swiss National Science Foundation (P300P2-158407, P300P2-174475). We gratefully acknowledge the computing resources on Marconi-Fusion under the EUROfusion project BigDFT4F, from the Swiss National Supercomputing Center in Lugano (project s700), the Extreme Science and Engineering Discovery Environment (XSEDE) (which is supported by National Science Foundation grant number OCI-1053575), the Bridges system at the Pittsburgh Supercomputing Center (PSC) (which is supported by NSF award number ACI-1445606), the Quest high performance computing facility at Northwestern University, and the National Energy Research Scientific Computing Center (DOE: DE-AC02- 05CH11231). ; Peer Reviewed ; Postprint (published version)

Tungsten (W) is an important and versatile transition metal and has a firm place at the heart of many technologies. A popular experimental technique for the characterization of tungsten and tungsten-based compounds is x-ray photoelectron spectroscopy (XPS), which enables the assessment of chemical states and electronic structure through the collection of core level and valence band spectra. However, in the case of tungsten metal, open questions remain regarding the origin, nature, and position of satellite features that are prominent in the photoelectron spectrum. These satellites are a fingerprint of the electronic structure of the material and have not been thoroughly investigated, at times leading to their misinterpretation. The present work combines high-resolution soft and hard x-ray photoelectron spectroscopy (SXPS and HAXPES) with reflected electron energy loss spectroscopy (REELS) and a multitiered ab initio theoretical approach, including density functional theory (DFT) and many-body perturbation theory (G0W0 and GW + C ), to disentangle the complex set of experimentally observed satellite features attributed to the generation of plasmons and interband transitions. This combined experiment-theory strategy is able to uncover previously undocumented satellite features, improving our understanding of their direct relationship to tungsten's electronic structure. Furthermore, it lays the groundwork for future studies into tungsten-based mixed-metal systems and holds promise for the reassessment of the photoelectron spectra of other transition and post-transition metals, where similar questions regarding satellite features remain. ; CK acknowledges the support from the Department of Chemistry, UCL. NKF acknowledges support from the Engineering and Physical Sciences Research Council (EP/L015277/1). AR acknowledges the support fromthe Analytical Chemistry Trust Fund for her CAMS-UK Fellowship. LER acknowledges support from an EPSRC Early Career Research Fellowship (EP/P033253/1). JL and JMK acknowledge funding from EPSRC under Grant No. EP/R002010/1 and from a Royal Society University Research Fellowship (URF/R/191004). This work used the ARCHER UK National Supercomputing Service via JL's membership of the HEC Materials Chemistry Consortium of UK, which is funded by EPSRC (EP/L000202). JJGM and SM acknowledge the support from the FusionCAT project (001-P-001722) cofinanced by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of total cost eligible, the access to computational resources at MareNostrum and the technical support provided by BSC (RES-QS-2020-3-0026). Part of this work was carried out using supercomputer resources provided under the EU-JA Broader Approach collaboration in the Computational Simulation Centre of International Fusion Energy Research Centre (IFERC-CSC) ; Peer Reviewed ; "Article signat per 13 autors/es: C. Kalha, L. E. Ratcliff, J. J. Gutiérrez Moreno, S. Mohr, M. Mantsinen, N. K. Fernando, P. K. Thakur, T.-L. Lee, H.-H. Tseng, T. S. Nunney, J. M. Kahk, J. Lischner, and A. Regoutz" ; Postprint (author's final draft)

Using the PION ICRH modelling code and comparisons against JET tokamak experiments, the effect of including pitch angle dependence within the RF diffusion operator on the fast ion particle distribution functions is quantified. It is found to be of greatest importance in cases of higher harmonic heating and lower heating ion mass, resulting in faster drop-off of the distribution's high energy tail. We see differences of several orders of magnitude in the high-energy range and significant non-linear alterations by several tens of percent to ion species power partition. ITER scenario operational parameters are also considered, and this improved treatment is shown to benefit anticipated ITER scenarios with second harmonic hydrogen heating, according to our predictions. PION's combination of benchmarked simplified wave physics and Fokker-Planck treatment offers modelling advantages. Since including the pitch angle dependence in the RF diffusion operator has not led to a significant increase in the required computing time when modelling different ICRF schemes in JET discharges, it has been made available within the production code. ; The CCFE part of this work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The BSC part of this project is co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014–2020 with a grant of 50% of total cost eligible. The authors are grateful to Jacob Eriksson for assistance with experimental data, to Lars-Göran Eriksson for discussions on the implementation of the new features, and to Colin Roach and Michael Fitzgerald for valuable comments on the manuscript. ; Peer Reviewed ; Postprint (published version)

In this work, we will explore the feasibility of porting a Particle-in-cell code (EUTERPE) to an ARM multi-core platform from the Mont-Blanc project. The used prototype is based on a system-on-chip Samsung Exynos 5 with an integrated GPU. It is the first prototype that could be used for High-Performance Computing (HPC), since it supports double precision and parallel programming languages. ; The research leading to these results has received funding from the European Com- munity's Seventh Framework Programme (FP7/2007-2013) under the Mont-Blanc Project (http://www.montblanc-project.eu), grant agreement no 288777. This work was supported in part by grant ENE2012-30832, Ministerio de Economía y Competitividad and carried out within the framework of the EUROfusion Consortium, receiving funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reect those of the European Commission. ; Peer Reviewed ; Postprint (published version)

In this work, we will explore the feasibility of porting a Particle-in-cell code (EUTERPE) to an ARM multi-core platform from the Mont-Blanc project. The used prototype is based on a system-on-chip Samsung Exynos 5 with an integrated GPU. It is the first prototype that could be used for High-Performance Computing (HPC), since it supports double precision and parallel programming languages. ; The research leading to these results has received funding from the European Com- munity's Seventh Framework Programme (FP7/2007-2013) under the Mont-Blanc Project (http://www.montblanc-project.eu), grant agreement no 288777. This work was supported in part by grant ENE2012-30832, Ministerio de Economía y Competitividad and carried out within the framework of the EUROfusion Consortium, receiving funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reect those of the European Commission. ; Peer Reviewed ; Postprint (published version)

We present significant improvements and validations of a deterministic neutron transport code (NEUTRO) dedicated to solving the Boltzmann Transport Equation. The code is integrated as a module in the Alya software package developed by the Barcelona Supercomputing Center which uses the Discrete Ordinates Method on angular coordinates, multi-group for energy discretization and FEM on unstructured meshes to treat special complex domains. The anisotropy of the scattering medium is introduced into the scattering kernel using real base expressions for spherical harmonics. In order to build the total cross-section and the respective group matrix for the elastic cross-section, we use the NJOY code. We test the solver using different geometries, orders of integration for the angular discretization and number of energy groups. Finally, we compare our results against benchmarks obtained from an NEA database that reported measurements of leakage spectra of several materials. ; This work has been partially carried out within the framework of the EUROlab4HPC and Severo Ochoa fellowship and has been partly co-financed by the European Union Regional Development Fund (ERDF) within the framework of the ERDF Operational Program of Catalonia 2014-2020. The authors would like to thank Dr A. Portone and Dr M. Fabbri for useful discussions. ; Peer Reviewed ; Postprint (author's final draft)