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This article is part of the themed collection: New Trends and Challenges in Surface Phenomena, Carbon Nanostructures and Helium Droplets.

This themed collection includes a collection of articles on new trends and challenges in surface phenomena, carbon nanostructures and helium droplets.

The excitation of low-energy electron–hole pairs is one of the most relevant processes in the gas–surface interaction. An efficient tool to account for these excitations in simulations of atomic and molecular dynamics at surfaces is the so-called local density friction approximation (LDFA). The LDFA is based on a strong approximation that simplifies the dynamics of the electronic system: a local friction coefficient is defined using the value of the electronic density for the unperturbed system at each point of the dynamics. In this work, we apply real-time time-dependent density functional theory to the problem of the electronic friction of a negative point charge colliding with spherical jellium metal clusters. Our non-adiabatic, parameter-free results provide a benchmark for the widely used LDFA approximation and allow the discussion of various processes relevant to the electronic response of the system in the presence of the projectile., 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. IT1246-19), the Spanish Ministerio de Ciencia e Innovación (MICIN) Grants No. PID2019-107396GB-I00/AEI/10.13039/501100011033 and PID2019-107338RB-C66/AEI/10.13039/501100011033, as well as the Severo Ochoa Program for Centres of Excellence (CEX-2018-000867-S). NK acknowledges the funding from Spanish MICIN through grant PID2019-107338RB-C61/AEI/10.13039/501100011033, as well as a María de Maeztu award to Nanogune, Grant CEX2020-001038-M funded by MICIN/AEI/10.13039/501100011033.

We present ab initio molecular dynamics simulations based on the density functional theory to study the alignment-dependent scattering of O from highly oriented pyrolytic graphite (HOPG). Results are obtained for 200 meV O molecules with different alignments impinging with an angle of incidence measured from a surface normal of 22.5° on a thermalized (110 and 300 K) graphite surface. The choice of these initial conditions in our simulations is made to perform comparisons with recent experimental results on this system. Our results show that a lower number of molecules initially aligned normally to the surface is reflected in the scattering plane compared to the number of molecules initially aligned parallel to the surface. This is not due to an increase in the trapping of end-on-aligned molecules but due to the fact that a large amount of them are scattered out-of-plane. Additionally, we find that the final translational energy of end-on molecules is around 10% lower than that of side-on molecules. We show that this is due to a more efficient energy transfer from the translational degree of freedom to internal degrees of freedom for end-on molecules, and not due to a more efficient energy transfer to the surface. The results of our simulations are in overall agreement with the experimental observations regarding the alignment dependence of the in-plane scattering probabilities and the energy loss of the reflected molecules., We acknowledge financial support by the Gobierno VascoUPV/EHU project IT1246-19 and the Spanish Ministerio de Ciencia, Innovacion y Universidades (Grant No. FIS2016-76471-P). This research was conducted in the scope of the Transnational Common Laboratory (LTC) “QuantumChemPhysTheoretical Chemistry and Physics at the Quantum Scale”

A high dimensional and accurate atomistic neural network potential energy surface (ANN-PES) that describes the interaction between one O

A high dimensional and accurate atomistic neural network potential energy surface (ANN-PES) that describes the interaction between one O2 molecule and a highly oriented pyrolytic graphite (HOPG) surface has been constructed using the open-source package (aenet). The validation of the PES is performed by paying attention to static characteristics as well as by testing its performance in reproducing previous ab initio molecular dynamics simulation results. Subsequently, the ANN-PES is used to perform quasi-classical molecular dynamics calculations of the alignment-dependent scattering of O2 from HOPG. The results are obtained for 200 meV O2 molecules with different initial alignments impinging with a polar incidence angle with respect to the surface normal of 22.5° on a thermalized (110 and 300 K) graphite surface. The choice of these initial conditions in our simulations is made to perform comparisons to recent experimental results on this system. Our results show that the scattering of O2 from the HOPG surface is a rather direct process, that the angular distributions are alignment dependent, and that the final translational energy of end-on molecules is around 20% lower than that of side-on molecules. Upon collision with the surface, the molecules that are initially aligned perpendicular to the surface become highly rotationally excited, whereas a very small change in the rotational state of the scattered molecules is observed for the initial parallel alignments. The latter confirms the energy transfer dependence on the stereodynamics for the present system. The results of our simulations are in overall agreement with the experimental observations regarding the shape of the angular distributions and the alignment dependence of the in-plane reflected molecules., We acknowledge financial support by the Gobierno Vasco-UPV/EHU project IT1246-19 and the Spanish Ministerio de Ciencia e Innovación [Grant No. PID2019-107396GB-I00/AEI/10.13039/501100011033], as well as Agencia Nacional de Promoción de la Investigación, el Desarrollo Tecnológico y la Innovación (project PICT-2016 2750).

The dissociation process of hydrogen molecules on W(110) was studied using density functional theory and classical molecular dynamics. We have calculated the dissociation probability for molecules with energies below 300 meV and analyzed the dynamics of the adsorption process. Our results show that the fate of each trajectory is determined at distances relatively far from the surface, at roughly 2–2.5 Å. This distance varies slightly with the initial kinetic energy of the molecule. Part of our simulations include van der Waals dispersion effects in the interaction between molecule and surface. We present a comparison between these results and other theoretical and experimental results previously published. The inclusion of the van der Waals term provokes an increase in the far-distance attraction that is compensated by a stronger repulsion at short distances. The combination of both effects appreciably decreases the value of the dissociation probability. The successful comparison of our results with experimental information confirms that the methodology employed can be considered as a rich and accurate instrument to study the dissociation of hydrogen on surfaces., A. R. F. acknowledges financial support by the University of Bordeaux. This work was conducted in the scope of the transborder joint Laboratory “QuantumChemPhys: Theoretical Chemistry and Physics at the Quantum Scale” (ANR-10-IDEX-03-02). 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. IT1246-19) and the Spanish Ministerio de Ciencia e Innovación (PID2019-107396GB-I00/AEI/10.13039/501100011033).

The classical trajectory method in a quantum spirit assigns statistical weights to classical paths on the basis of two semiclassical corrections: Gaussian binning and the adiabaticity correction. This approach was recently applied to the heterogeneous gas-surface reaction between H2 in its internal ground state and Pd(111) surface e.g. [A. Rodríguez-Fernández et al., J. Phys. Chem. Lett., 2019, 10, 7629]. Its predictions of the sticking and state-resolved reflection probabilities were found to be in surprisingly good agreement with those of exact quantum time-dependent calculations where standard quasi-classical trajectory calculations failed. We show in this work that the quality of the previous calculations is maintained or even improved when H2 is rotationally excited.

Using density functional theory combined with an evolutionary algorithm for crystal structure prediction, we study the elastic and electronic properties of various multi-principal element alloys that are based on CoCrFeNi. In total, nine quinary and one senary CoCrFeNiX (X=Ti, V, Mn, MnV, Cu, Zr, Nb, Mo, Al, Al2) alloys are studied along with the base CoCrFeNi alloy. The aim of the current study is twofold. First, we test and confirm the ability of the presented methodology to predict the crystal structure of the multi-principal element alloys based on Co, Cr, Fe, and Ni elements. Second, we calculate and compare the elastic properties of the CoCrFeNiX alloys, as well as their electronic properties, in an attempt to establish possible correlations between them. Taking CoCrFeNi as the reference alloy, our first-principles calculations of various elastic moduli (bulk, Young, and shear moduli) show that only the bulk moduli of the alloys with Cu, Mo, or Nb (in this order) are expected to be larger. Furthermore, our comparative analysis of the CoCrFeNiX alloys containing partially filled 3d and 4d elements shows that the filling of the d-shell causes a general increase in all the elastic moduli. The only exception is the decreasing behavior of the bulk modulus in the case of alloys with partially filled 3d elements., This work was partially financed by Gobierno Vasco through the ELKARTEK Project Nos. KK-2017/00007 and KK-2018/00015, the Spanish Ministerio de Economía, Industria y Competitividad Grant No. FIS2016-76471-P, and the Gobierno Vasco-UPV/EHU Project No. IT-1246-19.

In this chapter, we will provide the theoretical foundations on which the local-density friction approximation (LDFA) is based and examples of its application to gas–surface interaction problems. With this aim, first in Sect. 28.2 we will review the derivation of the stopping power (energy lost per unit path length) for an atom or molecule traveling through a uniform electron gas in the strong coupling limit, i. e., when its velocity is lower than the Fermi velocity of the system. Real systems present electronic density nonlinearities. For this reason in Sect. 28.3, we show how this method for calculating the stopping power has been successful to reproduce and explain experimental energy-loss measurements for ions/atoms traveling through real solids and interacting with metal surfaces. The last part of Sect. 28.3 is devoted to the description of the LDFA method that accounts for the effect of energy losses in the dynamics of thermal and hyperthermal gas particles interacting with metal surfaces. Its implementation both in molecular dynamics performed in precalculated potential energy surfaces (PESs) and in ab-initio molecular dynamics is also discussed. Finally, an overview of the knowledge acquired during last years by the application of the LDFA will be presented in Sect. 28.4. In particular, we will analyze the importance of electron–hole (e–h) pair excitations in different gas–surface elementary processes that involve atoms and molecules of practical interest, such as H, N, H2, N2, and H2O. The analysis will mostly review the results obtained for the dissociative and nondissociative adsorption, for the Eley–Rideal and hot-atom recombinations and for the scattering of these gas species on different metal surfaces. As a general conclusion, it will be shown that e–h pair excitations are typically relevant for long-lasting processes. The last part of this section will review recent applications of the LDFA to model the desorption dynamics of atoms or molecules induced by femtosecond laser pulses. A summary of this chapter is provided in Sect. 28.5.

San Sebastian (Donostia in the Basque language) is a beautiful, medium-sized European city of about 200,000 inhabitants located at the heart of the Basque Country, next to the Atlantic Ocean and the Pyrenees. Long known as a tourist and culinary destination, San Sebastian has recently become a city of science and technology, with a strong focus on nanoscience research and characterized by an interdisciplinary approach and the support of intense industrial activity in the region. The San Sebastian nanoscience community has contributed considerably to ACS Nano with more than 100 publications during the past decade, some of which have already had significant impact and are highlighted in this virtual issue. This activity has turned this small point at the Basque coastline into a worldwide “nano”-pole for a variety of focused areas of nanoscience research.

The TiZrNbTaMo multi-principal element alloy has been postulated as a new potential material for biomedical applications, such as orthopedic implants. Besides the good biocompatibility of the constituent atoms, the TiZrNbTaMo alloy also exhibits excellent corrosion resistance and mechanical properties, according to recent experimental studies. Motivated by these experiments, here we investigate with density functional theory (DFT) the structure, as well as the elastic and electronic properties, of the equiatomic and nearly-equiatomic TiZrNbTaMo alloys. By combining evolutionary algorithms with DFT calculations of the energy, we can correctly predict the crystal structures of the two phases that are identified in experiments. The corresponding elastic properties, which are also calculated with DFT, are in good qualitative agreement with the experimental observations. The analysis of the electronic properties allows us to explain the differences in the elastic moduli between the two phases in terms of the differences in both the electron density distribution and the bonding-states occupation., The work was partially financed by Gobierno Vasco through the ELKARTEK Project KK-2017/00007 and Spanish Ministerio de Economía, Industria y Competitividad [grant number FIS2016-76471-P].

This work was partially supported by the Basque Departamento de Educacion, Universidades e Investigacion, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economia y Competitividad (Grants No. FIS2016-76471-P and No. MAT2016-78293-C6-4-R). We are indebted to the Brazilian agencies CAPES, CNPq, and FAPERGS for partial support of the experimental part of this work.

Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe, the photoemission events are time ordered with rising initial-state angular momentum. Including intra-atomic electron-electron interaction and angular momentum of the initial localized state yields excellent agreement between theory and experiment. This has required a revision of existing models for solid-state photoemission, and thus, attosecond time-resolved photoemission from solids provides important benchmarks for improved future photoemission models., This work was supported by the German Research Foundation (DFG) within the Collaborative Research Center (SFB) 613 (F.S., P.B., W.P., and U.H.), the Priority Programs SPP 1931 (C.S., M.H., and W.P.), and SPP 1840 (St.F., S.N., and W.P.); the Basque Government (grant IT-756-13 UPV/EHU) (V.M.S., E.E.K., R.D.M., P.M.E., and A.K.K.); and the Spanish Ministerio de Economía y Competitividad (grants FIS2016-76617-P and FIS2016-76471-P) (V.M.S., E.E.K., R.D.M., P.M.E., and A.K.K.) and Fondo Europeo de Desarrollo Regional (FEDER) (CTQ2016- 80375-P) (M.T.-S.). N.M.K. acknowledges hospitality and financial support from the theory group in cooperation with the small quantum systems (SQS) research group of European XFEL.

Accurately modeling surface temperature and surface motion effects is necessary to study molecule-surface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics., The Leiden group thanks the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands Organisation for Scientific Research, NWO) and the European Research Council for supporting this research through a TOP grant and a ERC-2013 advanced grant (Grant No. 338580), respectively. O.G., R.D.M., and M.A. acknowledge financial support by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economía y Competitividad (Grant No. FIS2013-48286-C2-2-P). O.G. acknowledges the IDEX Bordeaux (No. ANR-10-IDEX-03-02) and Euskampus for fundings.

One of the main challenges in theoretical gas-surface studies is to incorporate into the dynamics energy exchange to both lattice vibrations and electronic excitations, keeping the accuracy of a multidimensional ab-initio potential energy surface for describing the gas/metal interaction. In this chapter, we review some recent advances in the subject and will present a theoretical framework recently developed that allows to evaluate within a full dimensional dynamics the combined contribution of both excitation mechanisms. This objective has been accomplished by combining the Generalized Langevin Oscillator model for phonon excitations and the Local Density Friction Approximation for electronic excitations. The inclusion of both effects allows one to address such fundamental questions as which is the relative importance of phonon and electron-hole pair excitations as energy dissipation channels and to what extent the adiabatic calculation can capture the basic physics of the dynamics and provide accurate results. Results on several systems and on different elementary gas-surface processes (dissociation, scattering, and molecular adsorption) are used to enrich the discussion. We show that, even when the energy dissipated is quantitatively significant, important aspects of the scattering dynamics are well captured by the adiabatic approximation., 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).

Using molecular dynamics simulations and potential energy surfaces of ab initio quality, we show that direct pickup of N adsorbates by gas-phase N is a highly efficient channel for N2 formation on Ag(111). This recombination process, called Eley-Rideal, was traditionally associated with lighter projectiles and regarded as marginal, but here, we obtain reactivities for N of ≳35% even at incident energies of a few eV. The good agreement found between simulated and published experimental energies of the desorbed N2 is a fingerprint of this otherwise elusive recombination. © 2013 American Chemical Society., Work 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 the Gipuzkoako Foru Aldundia and the European Commission (Grant No. FP7-PEOPLE-2010-RG276921). G.A.B. acknowledges ANPCYT (Grant No. PICT 2010-1558).

arXiv:1301.6489, We use time-dependent density functional theory to calculate the energy loss of an antiproton colliding with a small Al cluster previously excited. The velocity of the antiproton is such that non-linear effects in the electronic response of the Al cluster are relevant. We obtain that an antiproton penetrating an excited cluster transfers less energy to the cluster than an antiproton penetrating a ground state cluster. We quantify this difference and analyze it in terms of the cluster excitation spectrum. © 2013 Elsevier Ltd. All rights reserved., NEK acknowledges support from the CSIC JAE-predoc program, co-financed by the European Science Foundation. We also acknowledge the support of the Basque Departamento de Educación and the UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Economía y Competitividad (Grant No. FIS2010-19609-CO2-02) and the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa.

6 páginas, 5 figuras., Femtosecond and subfemtosecond time scales typically rule electron dynamics at metal surfaces. Recent advance in experimental techniques permits now remarkable precision in the description of these processes. In particular, shorter time scales, smaller system sizes, and spin-dependent effects are current targets of interest. In this article, we use state-of-the-art theoretical methods to analyze these refined features of electron dynamics. We show that the screening of localized charges at metal surfaces is created locally in the attosecond time scale, while collective excitations transfer the perturbation to larger distances in longer time scales. We predict that the elastic width of the resonance in excited alkali adsorbates on ferromagnetic surfaces can depend on spin orientation in a counterintuitive way. Finally, we quantitatively evaluate the electron–electron and electron–phonon contributions to the electronic excited states widths in ultrathin metal layers. We conclude that confinement and spin effects are key factors in the behavior of electron dynamics at metal surfaces., We acknowledge partial support by the Basque government, the University of the Basque Country UPV/EHU (Grant No. 9/UPV 00206.215-13639/2001), and the Spanish Ministerio de Educación y Ciencia (Grant FIS2007-66711-C02-00).