Suchergebnisse

We present a computer package aimed at the simulation of the electron–ion dynamics of finite systems, both in one and three dimensions, under the influence of time-dependent electromagnetic fields. The electronic degrees of freedom are treated quantum mechanically within the time-dependent Kohn–Sham formalism, while the ions are handled classically. All quantities are expanded in a regular mesh in real space, and the simulations are performed in real time. Although not optimized for that purpose, the program is also able to obtain static properties like ground-state geometries, or static polarizabilities. The method employed proved quite reliable and general, and has been successfully used to calculate linear and non-linear absorption spectra, harmonic spectra, laser induced fragmentation, etc. of a variety of systems, from small clusters to medium sized quantum dots. ; This work was partially supported by the RTN program of the European Union NANOPHASE (contract HPRN-CT-2000-00167), DGESIC (PB98-0345) and JCyL (VA28/99). G.B. acknowledges support by the U.S. Department of Energy under Contract No. E-FG-06-90ER-41132. ; Peer reviewed

10 pages, 7 figures.-- PACS nrs.: 34.35.+a, 34.20.Gj, 31.15.ee ; We present fully ab initio calculations of van der Waals coefficients for two different situations: (i) the interaction between hydrogenated silicon clusters and (ii) the interactions between these nanostructures and a nonmetallic surface (a silicon or a silicon carbide surface). The methods used are very efficient and allow the calculation of systems containing hundreds of atoms. The results obtained are further analyzed and understood with the help of simple models. These models can be of interest for molecular-dynamics simulations of silicon nanostructures on surfaces, where they can give a very fast yet sufficiently accurate determination of the van der Waals interaction at large separations. ; The authors were partially supported by the EC Network of Excellence NANOQUANTA (Grant No. NMP4-CT-2004–500198). S. Botti acknowledges financial support from French ANR (Grant No. JC0546741). A. Castro acknowledges financial support from the Deutsche Forschungsgemeinschaft within Grant No. SFB 658. X. Andrade acknowledges partial support from Marie Curie Action through the EU Programme (Grant No. HPMT-CT-2001–00368). M.A.L. Marques acknowledges partial support by the Portuguese FCT through Project No. PTDC/FIS/73578/2006. X. Andrade and A. Rubio acknowledge financial support from the Spanish Ministry of Education (Grant No. FIS2007–65702-C02–01) and Grupos Consolidados UPV/EHU of the Basque Country Government (2007). ; Peer reviewed

By first-principles time-dependent density-functional calculations, we show the relevance of relativistic effects to shape the photoabsorption cross section of small goldclusters (Aun,n <=8, andn = 20 ) and small nanowires(n<=7). The relativistic effects not only dictate the stabilization of planar geometries (as it has already been shown by treating the core electrons relativistically): The spin-orbit coupling also has a strong impact in the absorption spectra (resonances and oscillator strengths). This is especially true for nanowires, where the effect of spin orbit is large and not substantially reduced with the chain length, in contrast to more compact goldclusters where this spin-orbit effect tends to be quenched. These results have far reaching consequences in fields such as electronic transport, where goldnanowires are often used, but where spin-orbit effects are generally disregarded. ; This work was supported in part by the Deutsche Forschungsgemeinschaft (through SFB 658) , Spanish MEC ( FIS2007-65702-C02-01) , Grupos Consolidados UPV/EHU of the Basque Country Government ( IT-319-07) European Community e-I3 ETSF project, NANOQUANTA Network of Excellence, CONACyT Mexico Project No. J-59853-F , and the portuguese FCT ( Contract No. SFRH/BD/12712/2003 ). ; Peer reviewed

Many debates about environmental issues surfaced with the advent of the new coronavirus and social distancing. Therefore, the present article aimed to investigate air quality impacts in Rio de Janeiro, during social isolation period. In order to confirm air pollutants, decrease, for example NO and particulate material, documents such as legislations, technical standards, scientific articles published in this period, were analyzed during the studied period. Furthermore, the article sought to bring awareness about the short temporality of the air quality improvement, since without more sustainable forms of production, in a little while, those pollutants may increase again. ; Con la llegada del nuevo coronavirus y el distanciamiento social han surgido muchos debates sobre cuestiones ambientales. Por lo tanto, este estudio tenía como objetivo investigar los impactos causados en la calidad del aire en el estado de Río de Janeiro durante el período de aislamiento social. Para ello se analizaron documentos como la legislación, normas técnicas y artículos científicos publicados durante este período, que ayudaron a demostrar la reducción de contaminantes como el NO y las partículas durante el período estudiado. Además, trató de aportar reflexiones sobre la corta temporalidad de esta mejora de la calidad del aire, ya que sin formas de producción más sustentables, en un corto período de tiempo, los contaminantes pueden volver a aumentar. ; Muitos debates sobre as questões ambientais vieram à tona com o advento do novo coronavírus e do distanciamento social. Dessa maneira, o presente estudo teve como objetivo investigar os impactos causados na qualidade do ar no estado do Rio de Janeiro, durante o período de isolamento social. Para isso, foram analisados documentos, como legislações, normas técnicas e artigos científicos publicados nesse período, no qual auxiliaram na comprovação da redução de poluentes como o NO e o material particulado durante o período estudado. Ademais, buscou trazer reflexões sobre a curta temporalidade dessa melhoria da qualidade do ar, visto que sem formas de produção mais sustentáveis, em um curto espaço de tempo, os poluentes podem voltar a aumentar.

The optical response of the lowest energy isomers of theC 20 family is calculated using time-dependent density functional theory within a real-space, real-time scheme. Significant differences are found among the spectra of the different isomers, and thus we propose optical spectroscopy as a tool for experimental investigation of the structure of these important clusters. ; This work was partially supported by the RTN program of the European Union NANOPHASE (Contract No. HPRNCT-HPRNCT- 2000-00167), DGESIC (PB98-0345), and JCyL (VA28/99). A.C. acknowledges support from the MEC under the graduate fellowship program, and hospitality from the INT at the University of Washington, G.B. acknowledges support by the U.S. Department of Energy under Contract No. E-FG-06- 90ER-41132. ; Peer reviewed

This work is licensed under a Creative Commons Attribution 4.0 International License. ; Topological crystalline insulators are a type of topological insulators whose topological surface states are protected by a crystal symmetry, thus the surface gap can be tuned by applying strain or an electric field. In this paper we predict by means of ab initio calculations a new phase of Bi which is a topological crystalline insulator characterized by a mirror Chern number nM = −2, but not a Z2 strong topological insulator. This system presents an exceptional property: at the (001) surface its Dirac cones are pinned at the surface high-symmetry points. As a consequence they are also protected by time-reversal symmetry and can survive against weak disorder even if in-plane mirror symmetry is broken at the surface. Taking advantage of this dual protection, we present a strategy to tune the band-gap based on a topological phase transition unique to this system. Since the spin-texture of these topological surface states reduces the back-scattering in carrier transport, this effective band-engineering is expected to be suitable for electronic and optoelectronic devices with reduced dissipation. ; We acknowledge the computational support from the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant No. ACI-1053575. MGV and EVC acknowledge partial support from the Basque Country Government, Departamento de Educación, Universidades e Investigación (Grant No. IT-756-13), the Spanish Ministerio de Economía e Innovación (Grant No. FIS2010-19609-C02-01 and FIS2013-48286-C2-1-P), the FEDER funding, Saint Petersburg State University (Project No. 15.61.202.2015) and the Tomsk State University Competitiveness Improvement Program. FM thanks 'Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia FB 0807' and Fondecyt grant 1150806. AHR acknowledge the support of DMREF-NSF 1434897 and the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research under contract 54075-ND10. This work was supported by SPP 1666 of the Deutsche Forschungsgemeinschaft (DFG). ; Peer Reviewed

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. ; First-principles calculations within the framework of real-space time-dependent density functional theory have been performed for the complete chlorophyll (Chl) network of the light-harvesting complex from green plants, LHC-II. A local-dipole analysis method developed for this work has made possible the studies of the optical response of individual Chl molecules subjected to the influence of the remainder of the chromophore network. The spectra calculated using our real-space TDDFT method agree with previous suggestions that weak interaction with the protein microenvironment should produce only minor changes in the absorption spectrum of Chl chromophores in LHC-II. In addition, relative shifting of Chl absorption energies leads the stromal and lumenal sides of LHC-II to absorb in slightly different parts of the visible spectrum providing greater coverage of the available light frequencies. The site-specific alterations in Chl excitation energies support the existence of intrinsic energy transfer pathways within the LHC-II complex. ; The authors acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374), European Commission Project CRONOS (grant number 280879-2, CRONOS CP-7P7), Spanish Grant (FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13 and IT395-10), UPV/EHU (grant UFI11/45), COST Actions CM1204 (XLIC) and MP1306 (EUSpec). JJS gratefully acknowledges the Comissionat per a Universitats i Recerca del Departament dInnovacio, Universitats i Empresa, de la Generalitat de Catalunya for financial support, and the Marie Curie Cofund Action (FP7) of the European Union for the Beatriu de Pinos (2010 BP-A2-00024) postdoctoral fellowship. JAR acknowledges the fellowship of the UPV/EHU. JJPS acknowledges financial support from the National Institute Of General Medical Sciences of the National Institutes of Health (Award Number 1R44GM108085-01A1). BFM acknowledges financial support from the Portuguese Foundation for Science and Technology (CONT_DOUT/11/UC/ 405/10150/18/2008), the Donostia International Physics centre and the Centro de Fisica de Materiales, UPV/EHU, for financial support. ; Peer Reviewed

This Open Access Article is licensed under a Creative Commons Attribution 3.0 Unported Licence. ; Real-space grids are a powerful alternative for the simulation of electronic systems. One of the main advantages of the approach is the flexibility and simplicity of working directly in real space where the different fields are discretized on a grid, combined with competitive numerical performance and great potential for parallelization. These properties constitute a great advantage at the time of implementing and testing new physical models. Based on our experience with the Octopus code, in this article we discuss how the real-space approach has allowed for the recent development of new ideas for the simulation of electronic systems. Among these applications are approaches to calculate response properties, modeling of photoemission, optimal control of quantum systems, simulation of plasmonic systems, and the exact solution of the Schrödinger equation for low-dimensionality systems. ; XA acknowledges that part of this work was performed under the auspices of the U.S. Department of Energy at Lawrence Livermore National Laboratory under Contract DE-AC52-07A27344. XA and AA-G would like to thank the support received from Nvidia Corporation through the CUDA Center of Excellence program and the US Defense Threat Reduction Agency under contract no. HDTRA1-10-1-0046. DAS acknowledges support from the U.S. National Science Foundation graduate research program and IGERT fellowships, and from ARPA-E under grant DE-AR0000180. MJTO acknowledges financial support from the Belgian FNRS through FRFC project number 2.4545.12 "Control of attosecond dynamics: applications to molecular reactivity". NH and IT received support from a Emmy-Noether grant from Deutsche Forschungsgemeinschaft. JAR, AV, UDG, AHL and AR ackowledge financial support by the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374), European Commission project CRONOS (Grant number 280879-2 CRONOS CP-FP7), Marie Curie ITN POCAONTAS (FP7-PEOPLE-2012-ITN, project number 316633), OST Actions CM1204 (XLIC), and MP1306 (EUSpec), Spanish Grant (FIS2013-46159-C3-1-P) and Grupo Consolidado UPV/EHU del Gobierno Vasco (IT578-13). JAR acknowledges the Department of Education, Universities and Research of the Basque Government (grant IT395-10). AC acknowledges support from the grant FIS2013-46159-C3-2-P of the Spanish government. ; Peer Reviewed

International audience ; Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better ...

International audience ; Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better ...

International audience ; Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better ...

International audience ; Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better ...

International audience ; Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better ...

International audience ; Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better ...