Dynamic screening and energy loss of antiprotons colliding with excited Al clusters

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.Comment: 23 pages, 4 figures, to be published in Nuclear Instruments and Methods B as a proceeding of the IISC-19 Workshop on Inelastic Ion-Surface Collision

Nonlinear stopping effects of slow ions in a no-free-electron system: Titanium nitride

A recent experimental study of the energy losses of various ions in titanium nitride, in the low-energy range [M. A. Sortica, Sci. Rep. 9, 176 (2019)2045-232210.1038/s41598-018-36765-7], showed a striking departure of the measured values from those predicted by density functional theory. They suggested electron promotion in atomic collisions between dressed atoms as an explanation. In this Rapid Communication, we investigate the process of energy loss of slow ions in TiN using theoretical formulations that are based, on one side, on self-consistent models of nonlinear screening and quantum scattering theory, and on the other, on ab initio computations of the electron-density profile of titanium nitride. Two theoretical approaches are considered to determine the average energy transfer: One is based on the local-density approximation for the inhomogeneous electron gas corresponding to the calculated density of TiN, and the other is based on the Penn model for the convolution of the inhomogeneous electron-gas response based on a measured electron-loss function. Both approaches produce very similar results and are in remarkable agreement with the experimental data, indicating that the observed enhancement in the energy-loss values is due to the contribution of a range of electron densities in the TiN compound.Fil: Matias Da Silva, Flávio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Grande, P. L.. Universidade Federal do Rio Grande do Sul; BrasilFil: Vos, M.. The Australian National University; AustraliaFil: Koval, Peter. Donostia International Physics Center; EspañaFil: Koval, Natalia E.. Comisión de Investigaciones Científicas. Nanogune; EspañaFil: Arista, Nestor Ricardo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentin

Dynamic screening of a localized hole during photoemission from a metal cluster

Recent advances in attosecond spectroscopy techniques have fueled the interest in the theoretical description of electronic processes taking place in the subfemtosecond time scale. Here we study the coupled dynamic screening of a localized hole and a photoelectron emitted from a metal cluster using a semi-classical model. Electron density dynamics in the cluster is calculated with Time-Dependent Density Functional Theory and the motion of the photoemitted electron is described classically. We show that the dynamic screening of the hole by the cluster electrons affects the motion of the photoemitted electron. At the very beginning of its trajectory, the photoemitted electron interacts with the cluster electrons that pile up to screen the hole. Within our model, this gives rise to a significant reduction of the energy lost by the photoelectron. Thus, this is a velocity dependent effect that should be accounted for when calculating the average losses suffered by photoemitted electrons in metals.Comment: 15 pages, 5 figure

On-Surface Synthesis and Characterization of a High-Spin Aza-[5]-Triangulene

Triangulenes are open-shell triangular graphene flakes with total spin increasing with their size. In the last years, on-surface-synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive. In this work, we report the combined in-solution and on-surface synthesis of a large nitrogen-doped triangulene (aza-[5]-triangulene) and the detection of its high spin ground state on a Au(111) surface. Bond-resolved scanning tunneling microscopy images uncovered radical states distributed along the zigzag edges, which were detected as weak zero-bias resonances in scanning tunneling spectra. These spectral features reveal the partial Kondo screening of a high spin state. Through a combination of several simulation tools, we find that the observed distribution of radical states is explained by a quintet ground state (S = 2), instead of the expected quartet state (S = 3/2), confirming the positively charged state of the molecule on the surface. We further provide a qualitative description of the change of (anti)aromaticity introduced by N-substitution, and its role in the charge stabilization on a surface, resulting in a S = 2 aza-[5]-triangulene on Au(111).Comment: 8 pages with 4 figure

колективна монографія

Кримінальний процесуальний кодекс 2012 року: ідеологія та практика правозастосування: колективна монографія / за заг. ред. Ю. П. Аленіна ; відпов. за вип. І. В. Гловюк. - Одеса : Видавничий дім «Гельветика», 2018. - 1148 с

Measurement of the very rare K+→π+ννˉK^+ \to \pi^+ \nu \bar\nu decay

The decay K+→π+νν¯ , with a very precisely predicted branching ratio of less than 10−10 , is among the best processes to reveal indirect effects of new physics. The NA62 experiment at CERN SPS is designed to study the K+→π+νν¯ decay and to measure its branching ratio using a decay-in-flight technique. NA62 took data in 2016, 2017 and 2018, reaching the sensitivity of the Standard Model for the K+→π+νν¯ decay by the analysis of the 2016 and 2017 data, and providing the most precise measurement of the branching ratio to date by the analysis of the 2018 data. This measurement is also used to set limits on BR(K+→π+X ), where X is a scalar or pseudo-scalar particle. The final result of the BR(K+→π+νν¯ ) measurement and its interpretation in terms of the K+→π+X decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed

Electron dynamics in the interaction of atomic particles with spherical metal clusters

Doctoral Thesis submitted to the University of the Basque country for the degree of Doctor in physics.[EN]: In this thesis we apply time-dependent density functional theory (TDDFT) to study nonadiabatic phenomena in the interaction of charged particles, atoms, and molecules with spherical metallic clusters. These phenomena include the screening processes of projectiles in matter as well as the energy loss processes in a broad range of projectile velocities. In this thesis we focus on two related topics. The first part, described in Chapter 4, is devoted to the study of the coupled dynamic screening of a localized hole and a photoelectron emitted from a metal cluster or from an adsorbate on the surface of the cluster using a semi-classical model. The motion of the photoelectron is represented classically, while the electronic density dynamics in the cluster is calculated with TDDFT.We calculate the energy loss of the photoemitted electron moving away from the cluster with different velocities. As a result we see that the dynamic screening of the hole by the cluster electrons affects the motion of the photoemitted electron, namely it gives rise to a significant reduction of the energy lost by the photoelectron. In the second part we present the study of energy loss processes in the interaction of antiprotons and protons, as well as hydrogen dimers, with spherical clusters.[ES]: La estructura electrónica y las propiedades de los sólidos, superficies y nanoestructuras se pueden estudiar experimentalmente mediante diferentes técnicas espectroscópicas. En estos experimentos, el material se estudia mediante la interacción con partículas incidentes tales como electrones (espectroscopía electrónica de perdida de energía, EELS), fotones (espectroscopía de fotoemisión, PES), o iones (dispersión de iones, IS). Los proyectiles que penetran en el sólido o en la superficie crean excitaciones electrónicas en el material estudiado. La descripción cuantitativa de la dinámica de dichas partículas en las superficies y en los sólidos, así como la dinámica electrónica asociada, es esencial para la correcta interpretación de los resultados de los experimentos. Esta tesis está dedicada al estudio de las excitaciones electrónicas creadas durante la interacción de partículas cargadas y neutras con agregados metálicos. Las excitaciones electrónicas están asociadas con la disipación de la energía, lo que en nuestro caso significa la transferencia de energía cinética de un proyectil en movimiento a los electrónes de un agregado metálico o viceversa. En concreto, estudiamos los procesos de disipación en fenómenos físicos tales como el apantallamiento electrónico y el frenado de electrónes durante la fotoemisión, el apantallamiento electrónico y el frenado de iones y moléculas que atraviesan agregados metálicos y la fricción electrónica en superficies metálicas. La investigación de estos procesos nos permite obtener información sobre las propiedades de ambos, el material estudiado y el proyectil. La complejidad de estos procesos dinámicos en sólidos es un reto para los métodos teóricos. En esta tesis estudiamos la interacción de los agregados metálicos con partículas en movimiento utilizando una metodología eficiente basada en la teoría del funcional de la densidad dependiente del tiempo (TDDFT), un método ab initio basado en la mecánica cuántica que nos permite estudiar los procesos dinámicos que tienen lugar durante la interacción de las partículas con la materia en una amplia gama de velocidades de los proyectiles. Más concretamente, usamos el método de propagación de paquetes de onda (WPP), una herramienta eficaz para el tratamiento de procesos dinámicos en el dominio temporal. En esta tesis estudiamos estos fenómenos en dos contextos diferentes, aunque los métodos que usamos para este propósito son similares en ambos casos.I wish to acknowledge the financial support from Consejo Superior de Investigaciones Científicas (CSIC) through the Materials Physics Center (MPC/CFM) and from the Donostia International Physics Center (DIPC).Peer reviewe

Structure and properties of CoCrFeNiX multi-principal element alloys from ab initio calculations

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.Peer reviewe

Nanoplasmonics from large-scale ab initio calculations: opposite trends in Ag and Na clusters

Resumen del trabajo presentado a la NanoSpain Conference, celebrada en San Sebastián del 7 al 10 de marzo de 2017.An accurate description of electronic excitations is indispensable for understanding material properties and designing nanoscale devices. For instance, using large-scale TDDFT calculations, we have recently demonstrated the importance of taking into account the details of the atomic-scale structure and the quantization of electron transport in metal nanostructures in order to accurately describe their plasmonic properties. In this contribution we will compare the surface plasmon resonance of sodium and silver clusters within the same framework of iterative TDDFT. Recent progress in our implementation made it possible to perform calculations of large clusters of diameters ranging from a few Å to 4-5 nm (Figure 1), counting up to 5000 silver atoms and using only modest computational resources (a 32-core node with 500GB RAM). With these new capabilities, we have characterized the size-scaling of the SPR frequency for both sodium and silver clusters. As expected these two materials show opposite behaviors that can be related to the different spill out of charge at the surface and to the additional screening created by the 4d electrons in silver.Peer reviewe

Inelastic scattering of electrons in water from first principles: cross sections and inelastic mean free path for use in Monte Carlo track-structure simulations of biological damage.

Modelling the inelastic scattering of electrons in water is fundamental, given their crucial role in biological damage. In Monte Carlo track-structure (MC-TS) codes used to assess biological damage, the energy loss function (ELF), from which cross sections are extracted, is derived from different semi-empirical optical models. Only recently have first ab initio results for the ELF and cross sections in water become available. For benchmarking purpose, in this work, we present ab initio linear-response time-dependent density functional theory calculations of the ELF of liquid water. We calculated the inelastic scattering cross sections, inelastic mean free paths, and electronic stopping power and compared our results with recent calculations and experimental data showing a good agreement. In addition, we provide an in-depth analysis of the contributions of different molecular orbitals, species and orbital angular momenta to the total ELF. Moreover, we present single-differential cross sections computed for each molecular orbital channel, which should prove useful for MC-TS simulations