BUSCADOR RECOLECTA

The interaction among magnetic moments screened by conduction electrons drives quantum phase transitions between magnetically ordered and heavy-fermion ground states. Here, starting from isolated magnetic impurities in the Kondo regime, we investigate the formation of the finite size analogue of a heavy Fermi liquid. We build regularly-spaced chains of Co adatoms on a metallic surface by atomic manipulation. Scanning tunneling spectroscopy is used to obtain maps of the Kondo resonance intensity with sub-atomic resolution. For sufficiently small interatomic separation, the spatial distribution of Kondo screening does not coincide with the position of the adatoms. It also develops enhancements at both edges of the chains. Since we can rule out any other interaction between Kondo impurities, this is explained in terms of the indirect hybridization of the Kondo orbitals mediated by a coherent electron gas, the mechanism that causes the emergence of heavy quasiparticles in the thermodynamic limit., Financial support was provided by the Spanish Plan Nacional de I+ D+ i (grants MAT 2013-46593-C6-3-P, MAT2016-78293-C6-6-R, MAT2015-66888-C3-2-R, and FIS2015-64886-C5-3-P), Charles University (programme PRIMUS/Sci/09) and the European Union through programmes Interreg-POCTEFA (grant TNSI/EFA194/16) and H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598). M. M.-L., M. P., and D. S. acknowledge the use of SAI at Universidad de Zaragoza. R. R. acknowledges The Severo Ochoa Centers of Excellence Program (grant no. SEV-2017-0706) and Generalitat de Catalunya (grant no. 2017SGR1506 and the CERCA Programme).

The effects of the environment in nanoscopic materials can play a crucial role in device design. Particularly in biosensors, where the system is usually embedded in a solution, water and ions have to be taken into consideration in atomistic simulations of electronic transport for a realistic description of the system. In this work, we present a methodology that combines quantum mechanics/molecular mechanics methods (QM/MM) with the nonequilibrium Green’s function framework to simulate the electronic transport properties of nanoscopic devices in the presence of solvents. As a case in point, we present further results for DNA translocation through a graphene nanopore. In particular, we take a closer look into general assumptions in a previous work. For this sake, we consider larger QM regions that include the first two solvation shells and investigate the effects of adding extra k-points to the NEGF calculations. The transverse conductance is then calculated in a prototype sequencing device in order to highlight the effects of the solvent., The authors thank FAPESP and UFABC for financial support. A.R.R. acknowledges support from ICTP-SAIFR (FAPESP project 2011/11973-4) and the ICTP-Simons Foundation Associate Scheme. Computer time was provided by IFT/Unesp and USP/Sampa institutions. R.H.S. thanks the Swedish Research Council for financial support. P.O. acknowledges support from the Spanish MINECO (Grant FIS2015-64886-C5-3-P and the Severo Ochoa Centers of Excellence Program Grant SEV-2013-0295), Generalitat de Catalunya Government (2014SGR301), and EU H2020-EINFRA-5-2015 MaX Center of Excellence (Grant 676598). C.S.-N. acknowledges support from MINECO through the Ramon y Cajal Program., Peer reviewed

Interfaces are ubiquitous in materials science, and in devices in particular. As device dimensions are constantly shrinking, understanding the physical properties emerging at interfaces is crucial to exploit them for applications, here for spintronics. Using first-principles techniques and Monte Carlo simulations, we investigate the mutual magnetic interaction at the interface between graphene and an antiferromagnetic semiconductor BaMnO3. We find that graphene deeply affects the magnetic state of the substrate, down to several layers below the interface, by inducing an overall magnetic softening, and switching the in-plane magnetic ordering from antiferromagnetic to ferromagnetic. The graphene-
BaMnO3 system presents a Rashba gap 300 times larger than in pristine graphene, leading to a flavor of quantum anomalous Hall effect (QAHE), a hybrid QAHE, characterized by the coexistence of metallic and topological insulating states. These findings could be exploited to fabricate devices that use graphene to control the magnetic configuration of a substrate., Z.Z. acknowledges financial support by the Deutsche Forschungsgemeinschaft (DFG) Grant
No. ZA 780/3-1, the Ramon y Cajal MINECO program (Grant No. RYC-2016-19344), the EC H2020-EINFRA-5-2015 MaX Center of Excellence (Grant No. 676598), the Spanish MINECO (Grant No. FIS2015-64886-C5-3-P), the CERCA programme of the Generalitat de Catalunya (Grant No. 2017SGR1506), and by the Severo Ochoa programme (MINECO, Grant No. SEV-2013-0295). M.J.V. acknowledges funding from the Communauté française de Belgique ARC
grant (Grant No. AIMED 15/19-09). Y.M. acknowledges funding from the German Research Foundation (Deutsche Forschungsgemeinschaft), Grant No. MO 1731/5-1. This work has been also financially supported by the Deutsche Forschungsgemeinschaft (DFG) through the Collaborative Research Center SPP 1666. The authors acknowledge computer time from the PRACE-3IP and 4IP on resources Lindgren, Archer, and Salomon (EU Grants No. RI-312763 and
No. 653838), CECI, SEGI-ULg and Zenobe hosted by CENAERO (Grant No. GA 1117545), the JARA-HPC projects (No. jara0088, No. JIAS16, and No. JHPC39), the JARA-HPC Vergabegremium and VSR commission on the supercomputer JURECA at Forschungszentrum Jülich., Peer reviewed

An accurate and efficient general method to constrain the magnetization of individual atoms or groups of atoms within a fully relativistic non-collinear spin density functional theory formalism is presented and implemented within the SIESTA code. This approach can be applied to study a variety of complex magnetic configurations and to build effective magnetic Hamiltonians for multiscaling micromagnetic simulations. As an example, the method is applied to obtain constrained magnetic states for a Fe3 structure, and for a S = 1/2 kagome layer (vanadium oxyfluoride V7O6F18). Of paramount importance in spintronics is the control and manipulation of magnetic interactions between constituent species, characterized mainly by the pair-wise magnetic exchange tensor ${{ \mathcal J }}_{{ij}}$. By constraining the atomic magnetizations of an infinite Fe linear chain, the total selfconsistent energy values are mapped to a generalized Heisenberg model, obtaining not only the diagonal terms of ${{ \mathcal J }}_{{ij}}$ but also the off-diagonal contributions due to the explicit presence of the spin–orbit coupling in the formalism. The diagonal values of ${{ \mathcal J }}_{{ij}}$ promote short ranged ferromagnetic alignment whilst the non-zero off-diagonal values can lead to the formation of the spiral states in the chain, as expected from theory., ICN2 and ICMAB are supported by the Severo Ochoa Centers of Excellence Program (Grant No. SEV–2013–0295 and SEV–2015–0496), Spanish MINECO program (Grants No.FIS2015-64886-C5-3-P and FIS2015-64886-C5-4-P) and by the Generalitat de Catalunya (Grant No. 2017SGR1506). RC acknowledges the funding from the European Union’s Horizon 2020 research and innovation program under Marie SklodoswkaCurie grant agreement no. 665919 and EC H2020-EINFRA-5-2015 MaX Center of Excellence (Grant No. 676598)., Peer reviewed

While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π–π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties., The Catalan Institute of Nanoscience and Nanotechnology (ICN2) acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295) and funding from the CERCA Programme/Generalitat de Catalunya. Funding from the Spanish Ministry (MINECO/FEDER: MAT2015-68394-R NaCarFLOW, FIS2015-70862-P PHENTOM and FIS2015-64886-C5-3-P SIESTA) is also acknowledged. FC, BE, MP and PO acknowledge support from the EU Center of Excellence MaX-Materials Design at the Exascale (Grant No. 676598), Generalitat de Catalunya (Grant No. 2014SGR301) and supercomputing resources from the Red Española de Supercomputación (RES). ACA acknowledges Fundació Cellex de Barcelona for financial support., Peer reviewed

Development of novel 2D materials with singular and thrilling properties has aroused large interest due to the novel unexpected applications that can be derived from there. In this sense, coordination polymers (CPs) have appeared as matching candidates thanks to their rational chemical design and the added-value properties given by the presence of metal ions. This is the case of switchable spin-crossover systems that have been proposed as excellent candidates for data storage or sensing, among others. Here we report the delamination of crystals of the 2D spin-crossover (SCO) {[Fe(L1)2](ClO4)2}∝ (1) CP by liquid-phase exfoliation (LPE) in water. The application of this top-down technique results in the formation of flakes with controlled thicknesses, down to 1–2 nm thick (mostly mono- and bilayer), that retain the chemical composition and SCO interconversion of the bulk material. Moreover, these flakes can be handled as stable colloidal dispersions for many days. This allows for a controlled transfer to solid substrates and the formation of thermochromic polymeric films as a proof-of-concept of device. These first results will definitely open new venues and opportunities for the investigation and future integration of these original switchable 2D materials in devices., This work was supported by projects MAT2015-70615-R, CTQ2015-65439-R, and FIS2015-64886-C5-3-P from the Spanish Government funds and by European Regional Development Fund (ERDF). Funded by the CERCA Program/Generalitat de Catalunya. ICN2 is supported by the Severo Ochoa program from Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant SEV-2013-0295). Funded by the project 2014-SGR-301 (Generalitat de Catalunya). This work was supported by the Fonds National de la Recherche Scientifique-FNRS (PDR T.0102.15) and COST actions CM1305 and CA15128. M. M. D is a chargé de recherches from the F.R.S.-FNRS. S.S.-G. acknowledges the support from MINECO BES-2015-071492 grant. R.R. and P.O. acknowledge support from EU H2020-EINFRA-5-2015 MaX Center of Excellence (Grant 676598)., Peer reviewed

arXiv:1806.02999v1, Enhancing the spin–orbit interaction in graphene, via proximity effects with topological insulators, could create a novel 2D system that combines nontrivial spin textures with high electron mobility. To engineer practical spintronics applications with such graphene/topological insulator (Gr/TI) heterostructures, an understanding of the hybrid spin-dependent properties is essential. However, to date, despite the large number of experimental studies on Gr/TI heterostructures reporting a great variety of remarkable (spin) transport phenomena, little is known about the true nature of the spin texture of the interface states as well as their role on the measured properties. Here, we use ab initio simulations and tight-binding models to determine the precise spin texture of electronic states in graphene interfaced with a Bi2Se3 topological insulator. Our calculations predict the emergence of a giant spin lifetime anisotropy in the graphene layer, which should be a measurable hallmark of spin transport in Gr/TI heterostructures and suggest novel types of spin devices., ICN2 is funded by the CERCA Programme and Generalitat de Catalunya and is supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2013-0295). The authors
acknowledge funding from the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (project no. FIS2015-67767-P MINECO/FEDER,
FIS2015-64886-C5-3-P), the Secretaria de Universidades e Investigacion del Departamento de Economia y Conocimiento de la Generalidad de Catalunya (grant nos. 2014 SGR 58 and
2014 SGR 301), the European Union Seventh Framework Programme under grant agreement no. 696656 (Graphene Flagship), and the EU H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598)., Peer reviewed

The interaction among magnetic moments screened by conduction electrons drives quantum phase transitions between magnetically ordered and heavy-fermion ground states. Here, starting from isolated magnetic impurities in the Kondo regime, we investigate the formation of the finite size analogue of a heavy Fermi liquid. We build regularly-spaced chains of Co adatoms on a metallic surface by atomic manipulation. Scanning tunneling spectroscopy is used to obtain maps of the Kondo resonance intensity with sub-atomic resolution. For sufficiently small interatomic separation, the spatial distribution of Kondo screening does not coincide with the position of the adatoms. It also develops enhancements at both edges of the chains. Since we can rule out any other interaction between Kondo impurities, this is explained in terms of the indirect hybridization of the Kondo orbitals mediated by a coherent electron gas, the mechanism that causes the emergence of heavy quasiparticles in the thermodynamic limit., Financial support was provided by the Spanish Plan Nacional de I+D+i (grants MAT 2013-46593-C6-3-P, MAT2016-78293-C6-6-R, MAT2015-66888-C3-2-R, and FIS2015-64886-C5-3-P), Charles University (programme PRIMUS/Sci/09) and the European Union through programmes Interreg-POCTEFA (grant TNSI/EFA194/16) and H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598). M.M.-L., M.P., and D.S. acknowledge the use of SAI at Universidad de Zaragoza. R.R. acknowledges The Severo Ochoa Centers of Excellence Program (grant no. SEV-2017-0706) and Generalitat de Catalunya (grant no. 2017SGR1506 and the CERCA Programme)., Peer reviewed

Resumen del póster presentado al 10th International Symposium on Metallic Multilayers (MML), celebrado en Madrid (España) del 17 al 21 de junio de 2019., We have explored the realization of trilayer structures with single layer Graphene spacers and antiferromagnetically exchange coupled ferromagnetic layers, i.e. FM/Gr/FM, with close to zero net magnetization configurations. Studied systems were in-situ prepared via molecular-beam epitaxy in combination with intercalation procedures, to exchange couple ferromagnetic layers (Co, Fe, Ni) through a Graphene single layer spacer obtained by CVD on a Ir(111) surface. Alternatively, we have explored the possibility of fabricating a related system by incomplete intercalation, which yields interesting results for the case of Gr CVD on sputtered Pt on a sapphire single crystal. Our results provide an experimental demonstration of perpendicular antiferromagnetic exchange coupling of two Cobalt layers across a Graphene single spacing layer, as recently predicted and extending previous results. Furthermore, this constitutes a first step towards the engineering of compensated Graphene-based synthetic antiferromagnetic structures and nanostructures, which display close to zeronet macroscopic magnetization configurations that appear interesting for fundamental studies and may enclose potential for applications. Details on the surface preparation and investigation on these hybrid magnetic/Graphene heterostructures using soft x-ray absorption spectroscopy and magnetic dichroism measurements performed at ALBA synchrotron will be presented., This work was supported by Mineco “Retos program” under grants FIS2013-45469-C4-
3-R, FIS2016-78591- C3 (AEI/FEDER, UE), MAT2014-59315-R, and additionally
GenCat 2014SGR301, H2020 EINFRA-2015-1 676598 and Marie Skłodoswa-Curie no.
665919., Peer reviewed

Resumen del trabajo presentado al 10th International Symposium on Metallic Multilayers (MML), celebrado en Madrid (España) del 17 al 21 de junio de 2019., This work was supported by Mineco “Retos program” under grants FIS2013-45469-C4-
3-R, FIS2016-78591- C3 (AEI/FEDER, UE), MAT2014-59315-R, and additionally
GenCat 2014SGR301, H2020 EINFRA-2015-1 676598 and Marie Skłodoswa-Curie no.
665919., Peer reviewed

Silicon nanocrystals and nanowires have been extensively studied because of their novel properties and their applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. Here we discuss results from ab initio calculations for undoped and doped Si nanocrystals and nanowires, showing how theory can aid and improve comprehension of the structural, electronic and optical properties of these systems., S. O. acknowledges support/funding from University of Modena and Reggio Emilia under project “FAR2017INTERDISC”. S. O. and I. M. thank the Super-Computing Interuniversity Consortium CINECA for support and high-performance computing resources under the Italian Super-Computing Resource Allocation (ISCRA) initiative, PRACE for awarding us access to the resource MARCONI HPC cluster based in Italy at CINECA. I. M. acknowledges support/funding from European Union H2020-EINFRA-2015-1 and H2020-INFRAEDI-2018-1 programs under grant agreement No. 676598 and No. 824143, project MaX-MAterials at the eXascale. M. A. greatly acknowledges the Transnational Access Programme of the HPC-EUROPA3 (project HPC17PB9IZ). Some of the high-performance computing (HPC) resources for this project were granted by the Institut du development et des ressources en informatique scientifique (IDRIS) under the allocation A0040910089 via GENCI (Grand Equipment National de Calcul Intensif). This work was supported by the ANR HEXSIGE project (ANR-17-CE030-0014-01) of the French Agence Nationale de la Recherche. M. P. acknowledges INFN for financial support through the National project Nemesys. We also acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) and MICIU (Ministerio de Ciencia y Universidades) under Grants FEDER-MAT2017-90024-P, FIS2015-64886-C5-4-P and PGC2018-096955-B-C44-P, the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496 and the Generalitat de Catalunya under Grant 2017 SGR 1506., Peer reviewed

Density-functional theory methods and codes adopting periodic boundary conditions are extensively used in condensed matter physics and materials science research. In 2016, their precision (how well properties computed with different codes agree among each other) was systematically assessed on elemental crystals: a first crucial step to evaluate the reliability of such computations. In this Expert Recommendation, we discuss recommendations for verification studies aiming at further testing precision and transferability of density-functional-theory computational approaches and codes. We illustrate such recommendations using a greatly expanded protocol covering the whole periodic table from Z = 1 to 96 and characterizing 10 prototypical cubic compounds for each element: four unaries and six oxides, spanning a wide range of coordination numbers and oxidation states. The primary outcome is a reference dataset of 960 equations of state cross-checked between two all-electron codes, then used to verify and improve nine pseudopotential-based approaches. Finally, we discuss the extent to which the current results for total energies can be reused for different goals., This work was inspired and is supported in part by the European Union’s Horizon 2020 research and innovation programme
under grant agreement No. 676598 and grant agreement No. 824143 (European MaX Centre of Excellence “Materials design at
the Exascale”) and by NCCR MARVEL, a National Centre of Competence in Research, funded by the Swiss National Science
Foundation (grant number 205602). For the purpose of Open Access, a CC BY public copyright licence is applied to any
Author Accepted Manuscript (AAM) version arising from this submission.
We acknowledge Flaviano José dos Santos for useful discussions on the analysis of the smearing types and k-point
convergence, and Xavier Gonze, Marc Torrent, and François Jollet for useful discussions on PAW pseudopotentials.
M.F. and N.M. acknowledge the contribution of Sadasivan Shankar in early discussions about the use of 6 prototype oxides
as general platform to explore the transferability of pseudopotentials.
Work at ICMAB (E.B., A.G., V.D.) is supported by the Severo Ochoa Centers of Excellence Program (MCIN CEX2019-
000917-S), by grant PGC2018-096955-B-C44 of MCIN/AEI/10.13039/501100011033, “ERDF A way of making Europe”,
and by GenCat 2017SGR1506. We also thank the Barcelona Supercomputer Center for computational resources. V.D.
acknowledges support from DOC-FAM, European Union’s Horizon 2020 research and innovation programme under the Marie
Sklodowska-Curie grant agreement No 754397.
O.R. acknowledges travel support from WIEN2k (Technical University of Vienna).
The Jülich team (S.B., J.B., H.J., G.M., D.W) acknowledges support by the Joint Lab Virtual Materials Design (JL-VMD)
of the Forschungszentrum Jülich, the Helmholtz Platform for Research Software Engineering - Preparatory Study (HIRSE_PS),
the Joint Virtual Laboratory AI, Data Analytics and Scalable Simulation (AIDAS) of the Forschungszentrum Jülich and the
French Alternative Energies and Atomic Energy Commission, and we gratefully acknowledge the computing time granted
through JARA on the supercomputers JURECA83 at Forschungszentrum Jülich and CLAIX at RWTH Aachen University.
H.M and T.D.K (University of Paderborn) gratefully acknowledge the Gauss Centre for Supercomputing e.V. (www.gausscentre.
eu) for funding this project by providing computing time on the GCS Supercomputer JUWELS at Jülich Supercomputing
Centre (JSC).
S.P. and G.-M.R. (Université catholique de Louvain) acknowledge support from the F.R.S.-FNRS. Computational resources
have been provided by the PRACE-21 resources MareNostrum at BSC-CNS and by the Consortium des Équipements de Calcul
Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11 and
by the Walloon Region as well as computational resources awarded on the Belgian share of the EuroHPC LUMI supercomputer.
G.Ka. and S.V. received funding from the VILLUM Centre for the Science of Sustainable Fuels and Chemicals (9455)
from VILLUM FONDEN. Computational resources were provided by the Niflheim supercomputing cluster at the Technical
University of Denmark (DTU). They also thank Jens Jørgen Mortensen and Ask H. Larsen for the valuable discussions on
optimizing the workflow for the GPAW code.
S.C. acknowledges financial support from OCAS NV by an OCAS-endowed chair at Ghent University. The computational
resources and services used at Ghent University were provided the VSC (Flemish Supercomputer Center), funded by the
Research Foundation Flanders (FWO) and the Flemish Government – department EWI.
Accepted Manuscript by Nature Review Physics
Version of Record at https://doi.org/10.1038/s42254-023-00655-3
19/94
M.W. gratefully acknowledges computational resources provided by the Vienna Scientific Cluster (VSC). This research was
funded in part by the Austrian Science Fund (FWF) [P 32711].
E.F.L. would like to acknowledge resources provided by Sigma2 - the National Infrastructure for High Performance
Computing and Data Storage in Norway and support from the Norwegian Research Infrastructure Services (NRIS).
B.Z. is grateful to the UK Materials and Molecular Modelling Hub for computational resources, which is partially funded
by EPSRC (EP/P020194/1 and EP/T022213/1) and acknowledge the use of the UCL Myriad and Kathleen High Performance
Computing Facility (Myriad@UCL, Kathleen@UCL), and associated support services, in the completion of this work.
N.M., G.Pi., and A.G. acknowledge support from the European Union’s Horizon 2020 research and innovation programme
under grant agreement No. 957189 (BIG-MAP), also part of the BATTERY 2030+ initiative under grant agreement No. 957213.
G.P., J.Y. and G.-M.R. acknowledge support by the Swiss National Science Foundation (SNSF) and by the Fonds de la
Recherche Scientifique de Belgique (F.R.S.-FNRS) through the “FISH4DIET” Project (SNSF grant 200021E_206190 and
F.R.S.-FNRS grant T.0179.22).
G.P. acknowledges support by the Open Research Data Program of the ETH Board, under the Establish project “PREMISE”.
J.Y. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under grant
agreement No. 760173 (MARKETPLACE)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S)., Peer reviewed

We present a density functional theory study of the electronic structure of single-layer TiSe2, and focus on the charge density wave (CDW) instability present on this 2D material. We explain the $2\times 2$ periodicity of the CDW from the phonon band structure of the undistorted crystal, which is unstable under one of the phonon modes at the M point. This can be understood in terms of a partial band gap opening at the Fermi level, which we describe on the basis of the symmetry of the involved crystal orbitals, leading to an energy gain upon the displacement of the atoms following the phonon mode in a 2  ×  1 structure. Furthermore, the combination of the corresponding phonons for the three inequivalent M points of the Brillouin zone leads to the 2  ×  2 distortion characteristic of the CDW state. This leads to a further opening of a full gap, which reduces the energy of the 2  ×  2 structure compared to the 2  ×  1 one of a single M point phonon, and makes the CDW structure the most stable one. We also analyze the effect of charge injection into the layer on the structural instability. We predict that the 2  ×  2 structure only survives for a certain range of doping levels, both for electrons and for holes, as doping reduces the energy gain due to the gap opening. We predict the transition from the commensurate 2  ×  2 distortion to an incommensurate one with increasing wavelength upon increasing the doping level, followed by the appearance of the undistorted 1  ×  1 structure for larger carrier concentrations., This work was supported by Spanish MINECO (Grants
FIS2015-64886-C5-3-P and FIS2015-64886-C5-4-P,
and the Severo Ochoa Centers of Excellence Program
under Grants SEV-2013-0295 and SEV-2015-0496),
Generalitat de Catalunya (Grant 2017SGR1506 and
the CERCA Programme) and by the European Union
H2020-EINFRA-5-2015 MaX Center of Excellence
(Grant No. 676598). The calculations were performed
using the resources granted by Red Española de
Supercomputación (RES)., Peer reviewed

Monolayers of transition-metal dichalcogenide semiconductors present spin-valley locked electronic bands,
a property with applications in valleytronics and spintronics that is usually believed to be absent in their
centrosymmetric (as the bilayer or bulk) counterparts. Here we show that bulk 2H-MoS2 hides a spin-polarized
nature of states determining its direct band gap, with the spin sequence of valence and conduction bands expected
for its single layer. This relevant finding is attained by investigating the behavior of the binding energy of A and B
excitons under high pressure, by means of absorption measurements and density-functional-theory calculations.
These results raise an unusual situation in which bright and dark exciton degeneracy is naturally broken in a
centrosymmetric material. Additionally, the phonon-assisted scattering process of excitons has been studied by
analyzing the pressure dependence of the linewidth of discrete excitons observed at the absorption coefficient edge
of 2H-MoS2. Also, the pressure dependence of the indirect optical transitions of bulk 2H-MoS2 has been analyzed
by absorption measurements and density-functional-theory calculations. These results reflect a progressive closure
of the indirect band gap as pressure increases, indicating that metallization of bulk MoS2 may occur at pressures
higher than 26 GPa., Work inValenciawas supported by the SpanishGovernment
(Grants No. TEC2014-53727-C2-1-R and No. MAT2016-
75586-C4-1-P) and the Generalitat Valenciana (Grant No.
PROMETEOII/2014/059). Work in Bellaterra was supported
by Spanish MINECO (Grants No. FIS2015-64886-C5-3-P
and No. FIS2015-64886-C5-4-P), and the Severo Ochoa Centers
of Excellence Program (Grants No. SEV-2013-0295 and
No. SEV-2015-0496), Generalitat de Catalunya (Grant No.
2017SGR1506 and the CERCA Programme) and by the European
Union H2020-EINFRA-5-2015 MaX Center of Excellence
(Grant No. 676598). M.B.G. acknowledges Fellowship
No.UVINV-PREDOC13-110538 under the program “Atracció
de Talent, VLC-CAMPUS” of the University of Valencia., Peer reviewed

A density functional theory study concerning the origin of the
recently reported 2 2 charge density wave (CDW) instability in single-layer TiTe2
is reported. It is shown that, whereas calculations employing the semi-local
functional PBE favor the undistorted structure, the hybrid functional HSE06
correctly predicts a 2 2 distortion. The study suggests that the magnitude of
the semi-metallic overlap between the valence band top at and the conduction
band bottom at M is a key factor controlling the tendency towards the distortion.
It is also shown that tensile strain stabilizes a 2 2 CDW, and we suggest that
this fact could be further used to induce the instability in double-layers of TiTe2,
which in the absence of strain remain undistorted in the experiment. The driving
force for the CDW instability seems to be the same phonon mediated mechanism
acting for single-layer TiSe2, although in single-layer TiTe2 the driving force is
smaller, and the semimetallic character is kept below the transition temperature., This work was supported by Spanish MINECO
(Grants FIS2015-64886-C5-3-P and FIS2015-
64886-C5-4-P, and the Severo Ochoa Centers of
Excellence Program under Grants SEV-2017-0706
and SEV-2015-0496), Generalitat de Catalunya (Grant
2017SGR1506 and the CERCA Programme) and by
the European Union H2020-EINFRA-5-2015 MaX
Center of Excellence (Grant No. 676598). The work by
BG has been performed in the context of the Physics
PhD programme of the Universitat Autònoma de
Barcelona., Peer reviewed

Graphene nanoribbons (GNRs) are promising components in future nanoelectronics due to the large mobility of graphene electrons and their tunable electronic band gap in combination with recent experimental developments of on-surface chemistry strategies for their growth. Here, we explore a prototype 4-terminal semiconducting device formed by two crossed armchair GNRs (AGNRs) using state-of-the-art first-principles transport methods. We analyze in detail the roles of intersection angle, stacking order, inter-GNR separation, GNR width, and finite voltages on the transport characteristics. Interestingly, when the AGNRs intersect at θ=60°, electrons injected from one terminal can be split into two outgoing waves with a tunable ratio around 50% and with almost negligible back-reflection. The split electron wave is found to propagate partly straight across the intersection region in one ribbon and partly in one direction of the other ribbon, i.e., in analogy with an optical beam splitter. Our simulations further identify realistic conditions for which this semiconducting device can act as a mechanically controllable electronic beam splitter with possible applications in carbon-based quantum electronic circuits and electron optics. We rationalize our findings with a simple model suggesting that electronic beam splitters can generally be realized with crossed GNRs., The authors acknowledge financial support from FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (funded by the European Commission under Contract No. 610446), the Spanish Ministerio de Economia y Competitividad (MINECO) (Grant No. MAT2013-46593-C6-2-P), the Basque Departamento de Educacion, and the UPV/EHU (Grant No. IT-756-13). N.P. acknowledges financial support from No. EU H2020 Project No. 676598, “MaX: Materials at the eXascale” Center of Excellence in Supercomputing Applications., Peer Reviewed

We present novel methods implemented within the non-equilibrium Green function code (NEGF) TRANSIESTA based on density functional theory (DFT). Our flexible, next-generation DFT–NEGF code handles devices with one or multiple electrodes (N≥1) with individual chemical potentials and electronic temperatures. We describe its novel methods for electrostatic gating, contour optimizations, and assertion of charge conservation, as well as the newly implemented algorithms for optimized and scalable matrix inversion, performance-critical pivoting, and hybrid parallelization. Additionally, a generic NEGF “post-processing” code (TBTRANS/PHTRANS) for electron and phonon transport is presented with several novelties such as Hamiltonian interpolations, N≥1 electrode capability, bond-currents, generalized interface for user-defined tight-binding transport, transmission projection using eigenstates of a projected Hamiltonian, and fast inversion algorithms for large-scale simulations easily exceeding 10 atoms on workstation computers. The new features of both codes are demonstrated and bench-marked for relevant test systems., We acknowledge financial support from EU H2020 project no. 676598, “MaX: Materials at the eXascale” Center of Excellence in Supercomputing Applications, the Basque Departamento de Educación and the UPV/EHU (IT-756-13), the Spanish Ministerio de Economía y Competitividad (MAT2013-46593-C6-2-P, MAT2015-66888-C3-2-R, FIS2012-37549-C05-05, and FIS2015-64886-C5-4-P as well as the “Severo Ochoa” Program for Centers of Excellence in R&D SEV-2015-0496), the European Union FP7-ICT project PAMS (Contract No. 610446), and the Generalitat de Catalunya (2014 SGR 301)., Peer Reviewed

Supporting raw data for the article entitled "Real space manifestations of coherent screening in atomic scale Kondo lattices", to be accepted by Nature Communications, Financial support was provided by the Spanish Plan Nacional de I+D+i (grants MAT 2013-46593-C6-3-P, MAT2016-78293-C6-6-R, MAT2015-66888-C3-2-R and FIS2015-64886-C5-3-P), Charles University (programme PRIMUS/Sci/09) and the European Union through programmes Interreg-POCTEFA (Grant TNSI/EFA194/16) and H2020-EINFRA-5-2015 MaX Center of Excellence (Grant No. 676598). MML, MP and DS acknowledge the use of SAI at Universidad de Zaragoza. RR acknowledges The Severo Ochoa Centers of Excellence Program (Grant No. SEV-2017-0706) and Generalitat de Catalunya (Grant No. 2017SGR1506 and the CERCA Programme)., Peer reviewed

We present, within Kohn–Sham density functional theory calculations, a quantitative method to identify and assess the partitioning of a large quantum-mechanical system into fragments. We then show how within this framework simple generalizations of other well-known population analyses can be used to extract, from first-principles, reliable electrostatic multipoles for the identified fragments. Our approach reduces arbitrariness in the fragmentation procedure and enables the possibility to assess quantitatively whether the corresponding fragment multipoles can be interpreted as observable quantities associated with a system moiety. By applying our formalism within the code BigDFT, we show that the use of a minimal set of in situ-optimized basis functions allows at the same time a proper fragment definition and an accurate description of the electronic structure., We would like to thank Thierry Deutsch for valuable discussions and Fátima Lucas for providing various test systems and helpful discussions. This research used resources
of the Argonne Leadership Computing Facility,
which is a DOE Office of Science User Facility supported under Contract DEAC02-06CH11357. SM acknowledges
support from the European Centre of Excellence MaX (project ID 676598). LG acknowledges support from the EU ExtMOS project (project ID 646176) and the European
Centre of Excellence EoCoE (project ID 676629)., Peer Reviewed

In this paper, we address the decreasing performance of the FFTXlib, the Fast Fourier Transformation (FFT) kernel of Quantum ESPRESSO, when scaling to a full KNL node. An increased performance in the FFTXlib will likewise increase the performance of the entire Quantum ESPRESSO code one of the most used plane-wave DFT codes in the community of material science. Our approach focuses on, first, overlapping computation and communication and, second, decreasing resource contention for higher compute efficiency. In order to achieve this we use the OmpSs programming model based on task dependencies. We allow overlapping of computation and communication by converting all steps of the FFT into tasks following a flow dependency. In the same way, we decrease resource contention by converting each FFT into an individual task that can be scheduled asynchronously. In both cases, multiple FFTs can be computed in parallel. The task-based optimizations are implemented in the FFTXlib and show up to 10% runtime reduction on the already highly optimized version. Since the task scheduling is done dynamically during execution by the parallel runtime, not statically by the user, it also frees the user from finding the ideal parallel configuration himself., We gratefully acknowledge the support of the MaX and POP projects, which have received funding from the European Union’s Horizon 2020 research and innovation programme
under grant agreement No. 676598 and 676553, respectively., Peer Reviewed

We present CheSS, the “Chebyshev Sparse Solvers” library, which has been designed to solve typical problems arising in large-scale electronic structure calculations using localized basis sets. The library is based on a flexible and efficient expansion in terms of Chebyshev polynomials and presently features the calculation of the density matrix, the calculation of matrix powers for arbitrary powers, and the extraction of eigenvalues in a selected interval. CheSS is able to exploit the sparsity of the matrices and scales linearly with respect to the number of nonzero entries, making it well-suited for large-scale calculations. The approach is particularly adapted for setups leading to small spectral widths of the involved matrices and outperforms alternative methods in this regime. By coupling CheSS to the DFT code BigDFT, we show that such a favorable setup is indeed possible in practice. In addition, the approach based on Chebyshev polynomials can be massively parallelized, and CheSS exhibits excellent scaling up to thousands of cores even for relatively small matrix sizes., We gratefully acknowledge the support of the MaX (SM) and POP (MW) projects, which have received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement
No. 676598 and 676553, respectively. This work was also supported by the Energy oriented Centre of Excellence (EoCoE), grant agreement number 676629, funded within the Horizon2020 framework of the European
Union, as well as by the Next-Generation Supercomputer project (the K computer project) and the FLAGSHIP2020 within the priority study5 (Development of new fundamental technologies for high-efficiency
energy creation, conversion/storage and use) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. We (LG, DC, WD, TN) gratefully acknowledge the joint CEA-RIKEN collaboration action., Peer Reviewed

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

The interaction among magnetic moments screened by conduction electrons drives quantum phase transitions between magnetically ordered and heavy-fermion ground states. Here, starting from isolated magnetic impurities in the Kondo regime, we investigate the formation of the finite size analogue of a heavy Fermi liquid. We build regularly-spaced chains of Co adatoms on a metallic surface by atomic manipulation. Scanning tunneling spectroscopy is used to obtain maps of the Kondo resonance intensity with sub-atomic resolution. For sufficiently small interatomic separation, the spatial distribution of Kondo screening does not coincide with the position of the adatoms. It also develops enhancements at both edges of the chains. Since we can rule out any other interaction between Kondo impurities, this is explained in terms of the indirect hybridization of the Kondo orbitals mediated by a coherent electron gas, the mechanism that causes the emergence of heavy quasiparticles in the thermodynamic limit.