Spin-filtering effect in the transport through a single-molecule magnet Mn12_{12} bridged between metallic electrodes

Electronic transport through a single-molecule magnet Mn$_{12}$ in a two-terminal set up is calculated using the non-equilibrium Green's function method in conjunction with density-functional theory. A single-molecule magnet Mn$_{12}$ is bridged between Au(111) electrodes via thiol group and alkane chains such that its magnetic easy axis is normal to the transport direction. A computed spin-polarized transmission coefficient in zero-bias reveals that resonant tunneling near the Fermi level occurs through some molecular orbitals of majority spin only. Thus, for low bias voltages, a spin-filtering effect such as only one spin component contributing to the conductance, is expected. This effect would persist even with inclusion of additional electron correlations.Comment: Accepted for publication at J. Appl. Phy

First-principles study of electron transport through the single-molecule magnet Mn12

We examine electron transport through a single-molecule magnet Mn12 bridged between Au electrodes using the first-principles method. We find crucial features which were inaccessible in model Hamiltonian studies: spin filtering and a strong dependence of charge distribution on local environments. The spin filtering remains robust with different molecular geometries and interfaces, and strong electron correlations, while the charge distribution over the Mn12 strongly depends on them. We point out a qualitative difference between locally charged and free-electron charged Mn12

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnet Mn12

We examine theoretically coherent electron transport through the single-molecule magnet Mn$_{12}$, bridged between Au(111) electrodes, using the non-equilibrium Green's function method and the density-functional theory. We analyze the effects of bonding type, molecular orientation, and geometry relaxation on the electronic properties and charge and spin transport across the single-molecule junction. We consider nine interface geometries leading to five bonding mechanisms and two molecular orientations: (i) Au-C bonding, (ii) Au-Au bonding, (iii) Au-S bonding, (iv) Au-H bonding, and (v) physisorption via van der Waals forces. The two molecular orientations of Mn$_{12}$ correspond to the magnetic easy axis of the molecule aligned perpendicular [hereafter denoted as orientation (1)] or parallel [orientation (2)] to the direction of electron transport. We find that the electron transport is carried by the lowest unoccupied molecular orbital (LUMO) level in all the cases that we have simulated. Relaxation of the junction geometries mainly shifts the relevant occupied molecular levels toward the Fermi energy as well as slightly reduces the broadening of the LUMO level. As a result, the current slightly decreases at low bias voltage. Our calculations also show that placing the molecule in the orientation (1) broadens the LUMO level much more than in the orientation (2), due to the internal structure of the Mn$_{12}$. Consequently, junctions with the former orientation yield a higher current than those with the latter. Among all of the bonding types considered, the Au-C bonding gives rise to the highest current (about one order of magnitude higher than the Au-S bonding), for a given distance between the electrodes. The current through the junction with other bonding types decreases in the order of Au-Au, Au-S, and Au-H. Importantly, the spin-filtering effect in all the nine geometries stays robust and their ratios of the majority-spin to the minority-spin transmission coefficients are in the range of 10$^3$ to 10$^8$. The general trend in transport among the different bonding types and molecular orientations obtained from this study may be applied to other single-molecular magnets.Comment: Accepted for publication in Phys. Rev. B

Introducción al álgebra lineal

1 archivo PDF (37 páginas) ; 2a ed.El álgebra lineal es una de las ramas de las matemáticas más paradójicas: combina una aparente simplicidad con una cantidad enorme de aplicaciones que trascienden con mucho los confines de las ciencias físicas; combina también la facilidad de adaptarse a múltiples problemas reales con la generalización y utilización de muchos de sus conceptos de las áreas más abstractas de las matemáticas. Es posiblemente la materia que más modelos ha aportado a la práctica de las matemáticas aplicadas por ingenieros y otros profesionales. Por lo que Su comprensión y el manejo de las técnicas asociadas es uno de los principales objetivos de estudio

Aspectos organizativos de un centro escolar

La planificación inmediata de un centro educativo necesita de una serie de aspectos que inciden en la correcta organización escolar. Además de los documentos principales como son el PEC, la PGA o el RRI, los integrantes de la comunidad educativa necesitan información más ágil y directa sobre apartados organizativos del contexto de trabajo diario. El horario del profesorado, la vigilancia en los patios, el plan de sustituciones del profesorado, el calendario de reuniones y evaluación, el plan de acogida para alumnado extranjero, son entre otros, características que facilitan una organización escolar más eficaz

Simulation of evacuation with multi-agents on georeferenced layers with GAMA

This work deals with agent-based modeling withina geographical environment, it reviews concepts on Multi-agentsand Geographic Information Systems (GIS). It is oriented toperform a simulation that considers aspects of human behavior(through agents) during an evacuation, considering real restrictionsof the environment in which they are developed (GIS layers).This simulation is done in the GAMA1 platform, which allowsus to easily implement models based on agents and geographiclayers. It allows us to work with the attributes of the layers andto define constraints based on them. &nbsp

A multiphysics approach for modeling gas exchange in microperforated films for modified atmosphere packaging of respiring products

The objective of this work is to quantify, model and verify how the interactions between the respiring products and the surrounding atmosphere in a package affect the gas exchange through a microperforation. The pressure drop generated in a closed system by the metabolic activity of five different products has been determined by direct and indirect measurements. In this way, the estimated compensating hydrodynamic flows that can pass through the microperforated film ranged from 0.34 to 4.75 mL h(-1). A 3D model that considers the mass transfer coupled with the momentum transfer has been proposed to predict the gas concentration profiles around the microperforations originated by the diffusive and convective flows. A novel gas exchange measurement system, able to deliver small convective airflows comparable to those obtained for the different products and conditions, was assembled for the model verification. The model correctly predicts experimental data obtained for different convective flows

Sustentabilidad en las Denominaciones de Origen Protegidas (DOP) en la Unión Europea. Aproximaciones desde una revisión sistemática de la literatura

Protected Designations of Origin (PDO) safeguard and recognize food products with specific qualities resulting from their origins. This topic has been of recent interest to academics. Nonetheless, research that addresses sustainability in PDOs is still scarce. Thus, this paper aimed to identify the way the link between PDO and sustainability topic has been approached in recent research, especially on geographical spaces with a great history of use and exploitation of PDO figures, such as the European Union (EU). A systematic literature review methodology was selected by applying the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology, and by using Scopus, WoS, and Science Direct database between 2005 and 2021. From this screening process, 41 eligible studies were selected, and a qualitative and quantitative analysis was performed on the selected sample to address the following elements: (1) timeline growth on the field of knowledge; (2) food type product analyzed in the research; (3) research’s geographical location; (4) methodologies used, and (5) sustainability term’s combinations and its link to food type product. The results showed that sustainability in PDO’s research in the EU has experienced an upwards trend and is mostly carried out in those countries with the highest volume of PDOs registration, focusing mainly on dairy and oil products. Most of them applied mixed methodologies to assess an interdisciplinary sustainability perspective from its social, economic, and environmental dimension, being sustainable production systems the most common term used in the research.Las denominaciones de origen protegidas (DOP) salvaguardan y reconocen los productos alimenticios con cualidades específicas derivadas de su origen. Este tema ha sido de reciente interés para los académicos; no obstante, la investigación que aborda la sostenibilidad en las DOP es aún escasa. Por tanto, este trabajo tuvo como objetivo identificar la forma en que se ha abordado el vínculo entre DOP y sostenibilidad en investigaciones recientes, especialmente en espacios geográficos con una gran trayectoria en el uso y explotación de DOP, como la Unión Europea (UE). Se seleccionó una metodología de revisión sistemática de la literatura aplicando la metodología Preferred reporting items for systematic reviews and meta-analyzes (PRISMA) y se utilizó la base de datos de Scopus, WoS y Science Direct entre 2005 y 2021. De este proceso de selección, se escogieron 41 estudios elegibles y se realizó un análisis cualitativo y cuantitativo de la muestra para abordar los siguientes elementos: (1) tendencia temporal en el campo del conocimiento; (2) tipo de producto alimenticio analizado en la investigación; (3) ubicación geográfica de la investigación; (4) metodologías utilizadas; y (5) combinaciones de términos de sostenibilidad y su vínculo con el tipo de producto alimenticio. Los resultados mostraron que la investigación de la sostenibilidad en DOP en la UE presenta una tendencia creciente, y se lleva a cabo principalmente en aquellos países con el mayor volumen de registro de DOP, centrándose en productos lácteos y aceite, y aplicando metodologías mixtas para evaluar desde una perspectiva interdisciplinaria la dimensión social, económica y ambiental de la sostenibilidad, siendo los sistemas de producción sostenibles, el término más utilizado en la investigación