62 research outputs found
Spin-orbit proximity effect in graphene on metallic substrates: decoration vs intercalation with metal adatoms
The so-called spin-orbit proximity effect experimentally realized in graphene
(G) on several different heavy metal surfaces opens a new perspective to
engineer the spin-orbit coupling (SOC) for new generation spintronics devices.
Here, via large-scale density functional theory (DFT) calculations performed
for two distinct graphene/metal models, G/Pt(111) and G/Au/Ni(111), we show
that the spin-orbit splitting of the Dirac cones (DCs) in these stuctures might
be enhanced by either adsorption of adatoms on top of graphene (decoration) or
between the graphene and the metal (intercalation). While the decoration by
inducing strong graphene-adatom interaction suppresses the linearity of the G's
bands, the intercalated structures reveal a weaker adatom-mediated
graphene/substrate hybridization which preserves well-defined although
broadened DCs. Remarkably, the intercalated G/Pt(111) structure exhibits
splittings considerably larger than the defect-free case
A first principles study of thiol-capped Au nanoparticles: Structural, electronic, and magnetic properties as a function of thiol coverage
We have studied the stability of thiolated Au38 nanoparticles (NPs) via density functional theory based calculations varying the coverage from 0 up to 32 molecules. Three different initial core arrangements were considered for the cluster, spherical, tubular, and bi-icosahedral, while thiol groups were attached to the cluster via the sulfur atom either as single molecules or forming more complex staple motifs. After molecular dynamics runs several metastable configurations are found at each coverage thus allowing to analyze the properties of the NPs in the form of ensemble averages. In particular, we address the structural and electronic properties as a function of the number of thiols. The study emphasizes the strong influence of the core structure on the stability of the NPs, and its interplay with the thiol coverage and adsorption geometries. The magnetic properties of the NPs have also been explored via spin-polarized calculations including spin-orbit coupling. No evidence for the existence of a robust intrinsic ferromagnetism is found in any of the structures. © 2013 AIP Publishing LLC.This research was supported by the Spanish Ministry of Innovation and Science under Project No. MAT2010-18432.Peer Reviewe
Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data
We have developed an efficient and accurate formalism which allows the simulation at the ab initio level of inelastic electron tunneling spectroscopy data under a scanning tunneling microscope setup. It exploits fully the tunneling regime by carrying out the structural optimization and vibrational mode calculations for surface and tip independently. The most relevant interactions in the inelastic current are identified as the inelastic tunneling terms, which are taken into account up to lowest order, while all other inelastic contributions are neglected. As long as the system is under tunneling regime conditions and there is no physisorbed molecule on the surface or tip apex, this lowest order in inelastic tunneling (LOIT) approach reduces drastically the computational cost compared to related approaches while maintaining a good accuracy. Adopting the wide-band limit for both tip and surface further reduces calculation times significantly, and is shown to give similar results to when the full energy dependence of the Green's functions is taken into account. The LOIT is applied to the Cu(111)+CO system probed by a clean and a CO contaminated tip to find good agreement with previous works. Different parameters involved in the calculations such as basis sets, k sampling, tip-sample distance, or temperature, among others, are discussed in detail. © 2013 American Physical Society.J.C. acknowledges financial support from the Spanish Ministry of Innovation and Science under Contract No.MAT2010-18432.Peer Reviewe
High-Power-Density Energy-Harvesting Devices Based on the Anomalous Nernst Effect of Co/Pt Magnetic Multilayers
The anomalous Nernst effect (ANE) is a thermomagnetic phenomenon with potential applications in thermal energy harvesting. While many recent works studied the approaches to increase the ANE coefficient of materials, relatively little effort was devoted to increasing the power supplied by the effect. Here, we demonstrate a nanofabricated device with record power density generated by the ANE. To accomplish this, we fabricate micrometer-sized devices in which the thermal gradient is 3 orders of magnitude higher than conventional macroscopic devices. In addition, we use Co/Pt multilayers, a system characterized by a high ANE thermopower (∼1 μV/K), low electrical resistivity, and perpendicular magnetic anisotropy. These innovations allow us to obtain power densities of around 13 ± 2 W/cm3. We believe that this design may find uses in harvesting wasted energy, e.g., in electronic devicesThis work was supported by the Spanish Ministry of Science and Innovation through the projects PID2019-108075RB-C31 and MCIN/FEDER RTI2018-097895-B-C41. G.L.-P. acknowledges financial support from the Spanish Ministry of Science and Innovation through the Juan de la Cierva program (FJCI-2017-32370). J.M.-M. acknowledges the Spanish Ministry of Science, Innovation and Universities through FPU Program No. FPU18/01738
Spin excitations of individual magnetic dopants in an ionic thin film
Individual magnetic transition metal dopants in a solid host usually exhibit relatively small spin excitation energies of a few meV. Using scanning tunneling microscopy and inelastic electron tunneling spectroscopy (IETS) techniques, we have observed a high spin excitation energy around 36 meV for an individual Co substitutional dopant in ultrathin NaCl films. In contrast, the Cr dopant in the NaCl film shows much lower spin excitation energy around 2.5 meV. Electronic multiplet calculations combined with first-principles calculations confirm the spin excitation induced IETS, and quantitatively reveal the out-of-plane magnetic anisotropies for both Co and Cr. They also allow reproducing the experimentally observed redshift in the spin excitations of Co dimers and ascribe it to a charge and geometry redistribution.This research was supported by the National Natural Science Foundation of China (91961102, 11704057), the Shenzhen fundamental research funding (JCYJ20190806112206698), the starting funding from HIT Shenzhen (HA45001082), and the Research Foundation Flanders (G0D56.19N and G0A05.19N) and by the KU Leuven Research Council (C14/22/103). Financial support by the following Projects: RTI2018-097895-B-C41, PID2019-109539GB-C41 and PID2019-103910GB-I00, funded by MCIN/AEI/10.13039/501100011033/ and FEDER Una manera de hacer Europa, as well as GIU18/138 by Universidad del Pais Vasco UPV/EHU; IT-1246-19, IT986-16 and IT-1260-19 by Gobierno Vasco, is gratefully acknowledged
Structure and reactions of carbon and hydrogen on Ru(0001): A scanning tunneling microscopy study
The interaction between carbon and hydrogen atoms on a Ru(0001) surface was studied using scanning tunneling microscopy (STM), Density Functional Theory (DFT) and STM image calculations. Formation of CH species by reaction between adsorbed H and C was observed to occur readily at 100 K. When the coverage of H increased new complexes of the form CH+nH (n = 1, 2 and 3) were observed. These complexes, never observed before, might be precursors for further hydrogenation reactions. DFT analysis reveals that a considerable energy barrier exists for the CH+H {yields} CH{sub 2} reaction
Strontium hexaferrite platelets: a comprehensive soft X-ray absorption and Mössbauer spectroscopy study
IBERMÖSS-2019, Bilbao, 30-31 may 2019. --https://www.ehu.eus/es/web/ibermossmeetingStrontium ferrite (SFO, SrFe12O19) is a ferrite
employed for permanent magnets due to its high
magnetocrystalline anisotropy. Since its discovery
in the mid-20th century, this hexagonal ferrite has
become an increasingly important material both
commercially and technologically, finding a variety
of uses and applications. Its structure can be
considered a sequence of alternating spinel (S) and
rocksalt (R) blocks. All the iron cations are in the
Fe3+ oxidation state and it has a ferrimagnetic
configuration with five different cationic
environments for the iron (three octahedral sites, a
tetraedrical site and a bipiramidal site)[1,2].
We have studied the properties of SrFe 12O19 in the
shape of platelets, up to several micrometers in
width, and tens of nanometers thick, synthesized by
a hydrothermal method. We have characterized the
structural and magnetic properties of these platelets
by Mössbauer spectroscopy, x-ray transmission
microscopy (TMX), transmission electron
microscopy (TEM), x-ray diffraction (XRD),
vibrating-sample magnetometry (VSM), x-ray
absorption spectroscopy (XAS), x-ray circular
magnetic dichroism (XMCD) and photoemission
electron microscopy (PEEM). To the best of our
knowledge this is the first time that the x-ray
absorption spectra at the Fe L 2,3 edges of this
material in its pure form have been reported. The
Mössbauer results recorded from these platelets
both in the electron detection and transmission
modes have helped to understand the iron magnetic
moments determined by XMCD (Fig.1). The
experimental results have been complemented with
multiplet calculations aimed at reproducing the
observed XAS and XMCD spectra at the Fe L 2,3
absorption edge, and by density functional theory
(DFT) calculations to reproduce the oxygen K-
absorption edge. Finally the domain pattern
measured in remanence is in good agreement with
micromagnetic simulations [3]
Rab27a controls HIV-1 assembly by regulating plasma membrane levels of phosphatidylinositol 4,5-bisphosphate
During the late stages of the HIV-1 replication cycle, the viral polyprotein Pr55Gag is recruited to the plasma membrane (PM), where it binds phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and directs HIV-1 assembly. We show that Rab27a controls the trafficking of late endosomes carrying phosphatidylinositol 4-kinase type 2 α (PI4KIIα) toward the PM of CD4+ T cells. Hence, Rab27a promotes high levels of PM phosphatidylinositol 4-phosphate and the localized production of PI(4,5)P2, therefore controlling Pr55Gag membrane association. Rab27a also controls PI(4,5)P2 levels at the virus-containing compartments of macrophages. By screening Rab27a effectors, we identified that Slp2a, Slp3, and Slac2b are required for the association of Pr55Gag with the PM and that Slp2a cooperates with Rab27a in the recruitment of PI4KIIα to the PM. We conclude that by directing the trafficking of PI4KIIα-positive endosomes toward the PM, Rab27a controls PI(4,5)P2 production and, consequently, HIV-1 replication.Fil: Pereyra Gerber, Federico Pehuén. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; ArgentinaFil: Cabrini, Mercedes. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; ArgentinaFil: Jancic, Carolina Cristina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Paoletti, Luciana Elisa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Rosario. Instituto de BiologÃa Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias BioquÃmicas y Farmacéuticas. Instituto de BiologÃa Molecular y Celular de Rosario; ArgentinaFil: Banchio, Claudia Elena. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Rosario. Instituto de BiologÃa Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias BioquÃmicas y Farmacéuticas. Instituto de BiologÃa Molecular y Celular de Rosario; ArgentinaFil: Von Bilderling, Catalina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; ArgentinaFil: Sigaut, Lorena. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de MicroscopÃas Avanzadas; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Pietrasanta, Lia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de MicroscopÃas Avanzadas; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Duette, Gabriel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; ArgentinaFil: Freed, Eric O.. National Cancer Institute at Frederick; Estados UnidosFil: Basile, Genevieve de Saint. Institut National de la Santé et de la Recherche Médicale; FranciaFil: Moita, Catarina Ferreira. Instituto Gulbenkian de Ciencia; PortugalFil: Moita, Luis Ferreira. Instituto Gulbenkian de Ciencia; PortugalFil: Amigorena, Sebastian. Institute Curie; FranciaFil: Benaroch, Philippe. Institute Curie; FranciaFil: Geffner, Jorge Raúl. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; ArgentinaFil: Ostrowski, Matias. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas en Retrovirus y Sida. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas en Retrovirus y Sida; Argentin
Siesta: Recent developments and applications
A review of the present status, recent enhancements, and applicability of the SIESTA program is presented. Since its debut in the mid-1990s,
SIESTA’s flexibility, efficiency, and free distribution have given advanced materials simulation capabilities to many groups worldwide. The core
methodological scheme of SIESTA combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, and a realspace grid for the representation of charge density and potentials and the computation of their associated matrix elements. Here, we describe
the more recent implementations on top of that core scheme, which include full spin–orbit interaction, non-repeated and multiple-contact
ballistic electron transport, density functional theory (DFT)+U and hybrid functionals, time-dependent DFT, novel reduced-scaling solvers,
density-functional perturbation theory, efficient van der Waals non-local density functionals, and enhanced molecular-dynamics options. In
addition, a substantial effort has been made in enhancing interoperability and interfacing with other codes and utilities, such as WANNIER90 and
the second-principles modeling it can be used for, an AiiDA plugin for workflow automatization, interface to Lua for steering SIESTA runs, and
various post-processing utilities. SIESTA has also been engaged in the Electronic Structure Library effort from its inception, which has allowed
the sharing of various low-level libraries, as well as data standards and support for them, particularly the PSeudopotential Markup Language
definition and library for transferable pseudopotentials, and the interface to the ELectronic Structure Infrastructure library of solvers. Code
sharing is made easier by the new open-source licensing model of the program. This review also presents examples of application of the
capabilities of the code, as well as a view of on-going and future developments.
Published under license by AIP Publishing.Siesta development was historically supported by different Spanish National Plan projects (Project Nos. MEC-DGES-PB95-0202, MCyT-BFM2000-1312, MEC-BFM2003-03372, FIS2006-12117, FIS2009-12721, FIS2012-37549, FIS2015-64886-P, and RTC-2016-5681-7), the latter one together with Simune Atomistics Ltd. We are thankful for financial support from the Spanish Ministry of Science, Innovation and Universities through Grant No. PGC2018-096955-B.
We acknowledge the Severo Ochoa Center of Excellence Program [Grant Nos. SEV-2015-0496 (ICMAB) and SEV-2017-0706 (ICN2)], the GenCat (Grant No. 2017SGR1506), and the European Union MaX Center of Excellence (EU-H2020 Grant No. 824143).
P.G.-F. acknowledges support from Ramón y Cajal (Grant No. RyC-2013-12515). J.I.C. acknowledges Grant No. RTI2018-097895-B-C41.
R.C. acknowledges the European Union’s Horizon 2020 Research and Innovation Program under Marie Skłodoswka-Curie Grant Agreement No. 665919.
D.S.P, P.K., and P.B. acknowledge Grant No. MAT2016-78293-C6, FET-Open No. 863098, and UPV-EHU Grant No. IT1246-19.
V. W. Yu was supported by a MolSSI Fellowship (U.S. NSF Award No. 1547580), and V.B. and V.W.Y. were supported by the ELSI Development by the NSF (Award No. 1450280). We also acknowledge Honghui Shang and Xinming Qin for giving us access to the honpas code, where a preliminary version of the hybrid functional support described here was implemented.
We are indebted to other contributors to the Siesta project whose names can be seen in the Docs/Contributors.txt file of the Siesta distribution, and we thank those, too many to list, contributing fixes, comments, clarifications, and documentation for the code.Peer reviewe
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