Influence of the van der Waals interaction in the dissociation dynamics of N2 on W(110) from first principles

Under the terms of the Creative Commons Attribution (CC BY) license.Using ab initio molecular dynamics (AIMD) calculations, we investigate the role of the van der Waals (vdW) interaction in the dissociative adsorption of N2 on W(110). Hitherto, existing classical dynamics calculations performed on six-dimensional potential energy surfaces based on density functional theory (DFT), and the semi-local PW91 and RPBE [Hammer et al. Phys. Rev. B 59, 7413 (1999)] exchange-correlation functionals were unable to fully describe the dependence of the initial sticking coefficient on the molecular beam incidence conditions as found in experiments. N2 dissociation on W(110) was shown to be very sensitive not only to short molecule-surface distances but also to large distances where the vdW interaction, not included in semilocal-DFT, should dominate. In this work, we perform a systematic study on the dissociative adsorption using a selection of existing non-local functionals that include the vdW interaction (vdW-functionals). Clearly, the inclusion of the non-local correlation term contributes in all cases to correct the unrealistic energy barriers that were identified in the RPBE at large molecule-surface distances. Among the tested vdW-functionals, the original vdW-DF by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] and the ulterior vdW-DF2 give also an adequate description of the N2 adsorption energy and energy barrier at the transition state, i.e., of the properties that are commonly used to verify the quality of any exchange-correlation functional. However, the results of our AIMD calculations, which are performed at different incidence conditions and hence extensively probe the multi-configurational potential energy surface of the system, do not seem as satisfactory as the preliminary static analysis suggested. When comparing the obtained dissociation probabilities with existing experimental data, none of the used vdW-functionals seems to provide altogether an adequate description of the N2/W(110) interaction at short and large distances.The authors acknowledge financial support by the Gobierno Vasco-UPV/EHU project IT756-13 and the Spanish Ministerio de Economía y Competitividad (Grant No. FIS2013-48286-C02-02-P).Peer Reviewe

Dynamics of nitrogen scattering of N-covered Ag(111)

We analyze the reflection and adsorption dynamics of N atoms on a (1 × 1) N-covered Ag(111) surface, using an ab initio three-dimensional potential energy surface (3D PES) and classical molecular dynamics (MD) in the frozen and vibrating surface regimes. Our calculations reveal strong changes in the PES upon atomic N adsorption, which becomes much more corrugated than that of the clean Ag(111) surface. This apparently contradicts a key experimental finding made for atoms with incident average energy 〈E i〉 = 4.3 eV, namely that the N reflection dynamics on Ag(111) at N saturation coverage are quantitatively similar to those of clean Ag(111). In good agreement with the experiments, we find that the stronger PES corrugation of the N-covered Ag(111) surface does not affect the angular distribution of the scattered N atoms with that 〈E i〉 value. However, discrepancies are found in the final-to-initial average energy ratios, 〈E f〉/〈E i〉, at grazing outgoing angles. Upon examination of the adsorption trajectories, it can be inferred that gas N is likely to react with adsorbed N. MD shows that this >pickup> mechanism is particularly effective for slow atoms and could be behind the experimental 〈E f〉/〈E i〉 values. © 2012 American Chemical Society.M.B.-R. acknowledges financial support from the Gipuzkoako Foru Aldundia and the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement FP7-PEOPLE-2010-RG276921. Work was also supported by the Gobierno Vasco-UPV/EHU project IT-366-07 and the Spanish MICINN project FIS2010-19609-C02-02.Peer Reviewe

Energy dissipation channels in the adsorption of N on Ag(111)

6 páginas, 6 figuras.We theoretically study the competition between different energydissipationchannels in the adsorption of N atoms on Ag(1 1 1) surfaces. The three-dimensional potential energy surface that describes the interaction between the N atoms and the metal surface is built from density functional theory calculations. Classical dynamics simulations are subsequently performed to evaluate the adsorption probabilities. The contribution of electron–hole pairs excited in the surface during the adsorption process is included in the simulation by an electronic friction coefficient. Phonon excitations are also considered through the Generalized Langevin Oscillator model. We show that the role of the two channels during the adsorption dynamics is very different: phonons are responsible for determining the adsorption probability but electronic excitations are relevant at a later stage to fix the N atoms to the adsorption positions. We conclude that a theoretical model that intrinsically combines both energydissipationchannels is necessary to properly describe the full dynamics of the process.This work has been supported in part by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-366-07) and the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02).Peer reviewe

Scattering of nitrogen atoms off Ag(111) surfaces: A theoretical study

The study of the reflection of N atoms on a Ag(111) surface is performed by means of classical molecular dynamics and using an accurate three-dimensional potential energy surface, built from density functional theory calculations. The influence of energy loss channels is analyzed by including phonon and electron-hole pair excitations in the simulations. Our calculations show good agreement with recent experimental results. The broadness of the experimental angular distributions is due to the corrugation of the potential energy surface and is well reproduced by our model. Regarding the energy loss distributions, we show that the simulation of an effusive beam coupled to phonon excitations is required to obtain satisfactory results. This is due to dynamic effects that make the reflection process very dependent on the initial energy of N atoms. © 2013 American Chemical Society.This work has been supported in part by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-366-07), and the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02). M.B.-R. acknowledges financial support from the Gipuzkoako Foru Aldundia and the European Union seventh Framework Programme (FP7/2007-2013) under grant agreement no. FP7-PEOPLE-2010-RG276921.Peer Reviewe

Is the van der Waals interaction relevant to the dissociative dynamics of N2 on W(110)?

Resumen del póster presentado a la 15th International Conference on Vibrations at Surfaces, celebrada en Donsotia-San Sebastián (España) del 22 al 26 de junio de 2015.Using ab initio molecular dynamics (AIMD) calculations we investigate the role of the van der Waals interaction in the dissociative adsorption of N2 on W(110). Hitherto, existing classical dynamics calculations performed on six-dimensional potential energy surfaces based on density functional theory (DFT) and semi-local exchange-correlation functionals were unable to fully describe the dependence of the initial sticking coefficient on the molecular beam incidence conditions as found in experiments. N2 dissociation on W(110) was shown to be very sensitive not only to close molecule-surface distances, but also to the large distances region where the van der Waals interaction, not included in semilocal-DFT, should dominate. In this work, we perform a systematic study on the dissociative adsorption using a selected representation of existing non-local functionals that include the van der Waals interaction. Starting with a pure static analysis of the potential energy surfaces, we find that the original vdW-DF and vdW-DF2 functionals provide a rather good description of the experimental observations regarding the adsorption well and the balance between desorption and dissociation of the chemisorbed N2. In contrast, the optimized vdW-functionals proposed in Refs. share the limitations of the (semi-local) PW91 potential energy surface for this system, i.e., an excessively deep adsorption well from which the dissociation path compared with the desorption one is energetically favored. Unexpectedly, the results of the AIMD performed at different incidence conditions are not as satisfactory as the preliminary static analysis suggested. We have to conclude that none of the used vdW-functionals seem to provide altogether an adequate description of the N2/W(110) interaction at short and large distances.Peer reviewe

Canales de disipación de energía en procesos de reflexión y adsorción de átomos y moléculas en superficies metálicas

Resumen del trabajo presentado al VII Encontro Sul- Americano de Colisões Inelásticas na Matéria, celebrado en Gramado, RS (Brasil) del 27 al 30 de octubre de 2014.La descripción teórica de los procesos de reflexión y adsorción de átomos y moléculas diatómicas de energías térmicas en superficies metálicas se basa habitualmente en la aproximación adiabática. Gracias a formalismos teóricos capaces de alcanzar niveles muy altos de precisión (la teoría del funcional de la densidad, DFT, por ejemplo), la dinámica de estos procesos y las probabilidades con que pueden ocurrir en función de distintos parámetros presentes en el sistema, se pueden describir de forma cualitativa y, en muchos casos, cuantitativa. A pesar del éxito demostrado por la aproximación adiabática en este contexto, es cierto que este tipo de procesos puede y, en ocasiones, tiene que venir acompañado de distintos canales de disipación de energía. Los más importantes entre ellos son la excitación de pares electrón-hueco y la excitación de fonones en la superficie. En esta contribución describimos distintas aproximaciones teóricas que pueden servir para describir estos procesos disipativos, estudiamos distintos casos en los que tienen relevancia y discutimos la importancia relativa de cada uno de los canales de disipación con ejemplos concretos. En particular, nos centraremos, entre otros sistemas, en la pérdida de energía de átomos de nitrógeno en superficies de plata y en la pérdida de energía sufrida por átomos calientes de hidrógeno que se difunden en superficies de Paladio. Utilizaremos, por último, este mismo modelo teórico para estudiar la diferencia en la reactividad de la superficie de tungsteno cuando la constante de red se expande al crecer epitaxialmente encima de hierro.Peer Reviewe

Role of energy loss channels in the reactive and non-reactive dynamics of molecules and atoms on metal surfaces

Trabajo presentado al CECAM Workshop on: "Surface Dynamics: Beyond the Born-Oppenheimer Static Surface Approximation" celebrado en Zaragoza (España) del 24 al 26 de Octubre de 2012.We investigate the role played by electron-hole pair and phonon excitations in the interaction of reactive gas molecules and atoms with metal surfaces. We present a theoretical framework that allows us to evaluate within a full-dimensional dynamics the combined contribution of both excitation mechanisms while the gas particle-surface interaction is described by an ab initio potential energy surface. Examples of the application of the model to the study of different systems such as N2/W(110), N2/Fe(110), N2/Ag(111) and N/Ag(111) will be presented.Peer Reviewe

Electronic stopping of slow protons in oxides: Scaling properties

Electronic stopping of slow protons in ZnO, VO2 (metal and semiconductor phases), HfO2, and Ta2O5 was investigated experimentally. As a comparison of the resulting stopping cross sections (SCS) to data for Al2O3 and SiO2 reveals, electronic stopping of slow protons does not correlate with electronic properties of the specific material such as band gap energies. Instead, the oxygen 2p states are decisive, as corroborated by density functional theory calculations of the electronic densities of states. Hence, at low ion velocities the SCS of an oxide primarily scales with its oxygen density.Financial support of this work by the FWF (FWF-Project No. P22587-N20 and FWF-Project No. P25704-N20) is gratefully acknowledged. M. A. and J. I. J. acknowledge financial support by the Gobierno Vasco-UPV/EHU Project No. IT756-13, and the Spanish Ministerio de Economía y Competitividad (Grants No. FIS2013-48286-C02-02-P and FIS2016-76471-P). Fabrication and characterization of VO2 films at Vanderbilt University (CMG and RFH) was supported by a grant from the National Science Foundation (DMR-1207507). A research infrastructure fellowship of the Swedish Foundation for Strategic Research (SSF) under Contract No. RIF14-0053 supporting accelerator operation is acknowledged.Peer Reviewe

Transforming Cities: Opportunities and Challenges of Urban Regeneration in the Basque Country

Urban renewal policies seek to reverse physical, economic, and social decline in particular areas or neighborhoods—or in whole cities. Such policies are typically associated with public sector solutions to problems in the urban decline of former industrialized spaces that involve developing new economic activities by means of transforming such spaces once more into dynamic and attractive areas. Transforming Cities explores the multiple dimensions—incorporating physical-morphological, economic, functional, cultural, and residential elements—of urban renewal policies in the Basque Country and beyond. Individual chapters discuss urban regeneration in Bilbao, the legal framework of urban planning as a public function, the "smart city" model of sustainable and intelligent urban spaces, and culture as a strategic element for the reactivation, renewal, and development of new urban models, including the specific case of cultural heritage as a factor in the urban regeneration of Vitoria-Gasteiz, the legal implications of expropriating cultural assets, public and private collaboration to create cultural clusters, and, finally, the tensions that exist between institutionally driven visions of such transformation and more community-based approaches.This book was published with generous financial support from the Basque Government.Introduction by Arantxa Rodríguez and Joseba Juaristi ? 1. A Model of Regeneration? Urban Redevelopment and Policy-led Gentrification in Bilbao by Arantxa Rodríguez, Pedro Abramo, and Lorenzo Vicario ? 2. Some Reflections on Urban Revitilization and Regeneration in Central Asturias and Metropolitan Bilbao (1980-2010) by Joseba Juaristi Linacero ? 3. Urban Rehabilitation and the Necessity of Conservation: A New Approach by Pilar Garrido Gutiérrez ? 4. RDI and Urban Sustainability: The "Smart City" Model in the Basque Autonomous Community by Estibaliz Rodríguez Núñez and Iñaki Periàñez Cañadillas ? 5. Cultural Policy and Urban Regeneration: Exploring Conditions for Renewal Effectiveness by Beatriz Plaza ? 6. Cultural Heritage as a Factor in the Urban Regeneration of Vitoria-Gasteiz by Agustín Azkarate and Ander de la Fuente ? 7. The Expropriation of Cultural Assets in Urban Regeneration: On the Ruling of the European Court of Human Rights in Kozacio?lu v. Turkey, February 19, 2009 by Carmen Agoues Mendizabal ? 8. Urban Development and Commercial Invigoration through Cultural Clusters in Peripheral Neighborhoods of Bilbao by Gloria Aparicio and Jon Charterina ? 9. Power and Potential: Enclosure and Eruption in Bilbao by Igor Ahedo Gurrutxaga and Imanol Telleria ? Inde