A classical picture of subnanometer junctions: an atomistic Drude approach to nanoplasmonics

The description of optical properties of subnanometer junctions is particularly challenging. Purely classical approaches fail, because the quantum nature of electrons needs to be considered. Here we report on a novel classical fully atomistic approach, {\omega}FQ, based on the Drude model for conduction in metals, classical electrostatics and quantum tunneling. We show that {\omega}FQ is able to reproduce the plasmonic behavior of complex metal subnanometer junctions with quantitative fidelity to full ab initio calculations. Besides the practical potentialities of our approach for large scale nanoplasmonic simulations, we show that a classical approach, in which the atomistic discretization of matter is properly accounted for, can accurately describe the nanoplasmonics phenomena dominated by quantum effects.Comment: This article is licensed under a Creative Commons Attribution 3.0 Unported Licenc

Multiple Facets of Modeling Electronic Absorption Spectra of Systems in Solution

In this Perspective, we outline the essential physicochemical aspects that need to be considered when building a reliable approach to describe absorption properties of solvated systems. In particular, we focus on how to properly model the complexity of the solvation phenomenon, arising from dynamical aspects and specific, strong solute–solvent interactions. To this end, conformational and configurational sampling techniques, such as Molecular Dynamics, have to be coupled to accurate fully atomistic Quantum Mechanical/Molecular Mechanics (QM/MM) methodologies. By exploiting different illustrative applications, we show that an effective reproduction of experimental spectral signals can be achieved by delicately balancing exhaustive sampling, hydrogen bonding, mutual polarization, and nonelectrostatic effects

Mecanismos de la visión: una propuesta extracurricular para Educación Secundaria, con motivo de la celebración del Año Internacional de la Luz

Con motivo de la celebración del Año Internacional de la Luz numerosas iniciativa se han llevado a cabo y se siguen realizando por parte de diferentes entidades públicas y privadas con el objetivo de difundir los conocimientos, descubrimientos y tecnologías de la ciencia basada en la luz y su relación con la vida cotidiana, además de promover el interés hacia la cultura científica y las vocaciones científicas en el ámbito de la luz y sus aplicaciones. El presente Trabajo Final de Máster (TFM) se enmarca en el ámbito de una iniciativa puesta en marcha por profesores de la Universidad de Granada con el fin de llevar a centros educativos propuestas relacionadas con el Año Internacional de la Luz. En concreto, se propone la realización de una actividad extracurricular o complementaria cuya acción principal es la visita a un museo de ciencia interactivo: el Parque de las Ciencias de Granada. En línea con los principales objetivos de la alfabetización científica, el presente trabajo quiere ser una respuesta al nuevo planteamiento acerca del proceso de enseñanza/aprendizaje y, en general, una propuesta para que “los estudiantes aprendan algo que le interese de manera que continúen estudiando ciencia, tanto formalmente como informalmente, en el futuro” (DeBoer, 2000, p. 597). Siguiendo las directivas del Real Decreto 1105/2014, de 26 de diciembre, se ha enfocado la actividad extracurricular a contenidos de biología de 3º y 4º de Educación Secundaria Obligatoria (ESO), específicamente, la función vital de relación (receptores y efectores) y los mecanismos de la evolución, abarcando temas como los mecanismos de la visión, la biodiversidad o las estrategias de supervivencia relacionadas con la visión. El trabajo se compone de dos partes: la primera es la descripción de una acción piloto realizada en el IES-Luis Bueno Crespo de Armilla; la segunda es la propuesta definitiva desarrollada a partir de los resultados obtenidos en la parte experimental. La actividad no se limita a la visita al museo de ciencia, siendo reforzada por una fase preparatoria (anterior a la visita) y una de prolongación (posterior a la visita), realizadas en aula. Las observaciones recogidas durante la acción piloto pusieron de manifiesto justamente la necesidad de una fase preliminar bien desarrollada para alcanzar los objetivos fijados. Para facilitar la evaluación de las actividades grupales, tanto durante la visita al museo de ciencia como en aula, se ha desarrollado una rúbrica donde el docente puede asignar una calificación a cada grupo siguiendo unos criterios definidos. Además, mediante una escala de valoración y una lista de control, el propio alumnado participa en un proceso de autoevaluación (individual y grupal) y coevaluación. La propuesta desarrollada en el presente TFM nace, por un lado, de la idea de encontrar una herramienta atractiva para que los/as alumnos/as se acerquen a las temáticas científicas y a sus aplicaciones en la vida cotidiana y, por otro lado, de la búsqueda de un método de enseñanza basado en competencias. La implementación de la acción extracurricular diseñada se considera una posibilidad real que podría dar muy buenos resultados.On the occasion of the International Year of Light, different public and private entities have made and are still realizing several initiatives with the aim of disseminating knowledge, discoveries and technologies of light-based science and its relationship with everyday life, and promote the interest in scientific culture and vocations in scientific fields related to the light and its applications. This Master's Final Project (TFM) is part of an initiative proposed by professors of the Optics and Didactics of Experimental Sciences Departments of the University of Granada whose main purpose is to carry propositions concerning the International Year of Light to education centres, as secondary schools. In particular, the project proposed in the present manuscript consists on an extra-curricular (or complementary) activity whose main action is the visit to an interactive science museum: the Science Park of Granada. Accordingly with the main objectives of scientific literacy , this manuscript want to be a response to the new approach is rising up about the process of teaching/learning. Moreover, its general purpose is that "students could learn something that interests them so that they will continue to study science, both formally and informally, in the future " (DeBoer , 2000, p. 597). In agreement with the directives of the Real Decreto 1105/2014, 26th of December, the extracurricular activity was focused on the didactic content of biology of 3rd and 4th of Secondary Education (ESO), specifically, the relationship, as one of vital functions (receptors and effectors), and the mechanisms of evolution, including topics such as the mechanisms of vision, biodiversity and survival strategies related to the vision. The project consists of two parts: the first is the description of a pilot project conducted in the IES- Armilla Luis Bueno Crespo; the second is the final proposal developed on the base of the results obtained during the experimental part. The activity is not limited to the science museum visit, being reinforced by a preparatory phase (before the visit) and an extension phase (after the visit), performed in the classroom. The observations gathered during the pilot project have shown the need of a preliminary stage well developed to achieve the final objectives. To facilitate the evaluation of group activities both during the visit to the science museum and in the classroom, it was planned a rubrica by which the teacher can assign a mark to each group according to defined criteria. In addition, using a valuation scale and a checklist, the students themselves are involved in a process of self-assessment (individual and of group) and peer-assessment. The proposal developed in this TFM rises, on the one hand, from the idea to move students closer to scientific topics and their applications in everyday life by an attractive tool and, on the other hand, to find a teaching method based on competencies. The implementation of the extracurricular action designed is considered a real possibility that could give good results.Universidad de Granada. Departamento de Didáctica de las Ciencias Experimentales. Máster Universitario de Educación Secundaria Obligatoria y Bachillerato, Formación Profesional y Enseñanza de Idiomas. Especialidad en Biología-Geología, curso 2014-2015Grupo de Investigación Didáctica de las Ciencias Experimentales y de la Sostenibilidad (HUM613

Effective fully polarizable QM/MM approaches to compute Raman and Raman Optical Activity spectra in aqueous solution

Raman and Raman Optical Activity (ROA) signals are amply affected by solvent effects, especially in the presence of strongly solute-solvent interactions such as Hydrogen Bonding (HB). In this work, we extend the fully atomistic polarizable Quantum Mechanics/Molecular Mechanics approach, based on the Fluctuating Charges and Fluctuating Dipoles force field to the calculation of Raman and ROA spectra. Such an approach is able to accurately describe specific HB interactions, by also accounting for anisotropic contributions due to the inclusion of fluctuating dipoles. To highlight the potentiality of the novel approach, Raman and ROA spectra of L-Serine and L-Cysteine dissolved in aqueous solution are computed and compared both with alternative theoretical approaches and experimental measurements

Graphene Plasmonics: a Novel Fully Atomistic Approach for Realistic Structures

We demonstrate that the plasmonic properties of realistic graphene and graphene-based materials can effectively and accurately be modeled by a novel, fully atomistic, yet classical, approach, named $\omega$FQ. Such model is able to reproduce all plasmonic features of these materials, and their dependence on shape, dimension and fundamental physical parameters (Fermi energy, relaxation time and two-dimensional electron density). Remarkably, $\omega$FQ is able to accurately reproduce experimental data for realistic structures of hundreds of nanometers ($\sim$ 370.000 atoms), which cannot be afforded by any \emph{ab-initio} method. Also, the atomistic nature of $\omega$FQ permits the investigation of complex shapes, which can hardly be dealt with by exploiting widespread continuum approaches.Comment: 20 pages, 4 figure

Calculation of Linear and Non-linear Electric Response Properties of Systems in Aqueous Solution: A Polarizable Quantum/Classical Approach with Quantum Repulsion Effects

We present a computational study of polarizabilities and hyperpolarizabilities of organic molecules in aqueous solutions, focusing on solute-water interactions and the way they affect a molecule's linear and non-linear electric response properties. We employ a polarizable quantum mechanics/molecular mechanics (QM/MM) computational model that treats the solute at the QM level while the solvent is treated classically using a force field that includes polarizable charges and dipoles, which dynamically respond to the solute's quantum-mechanical electron density. Quantum confinement effects are also treated by means of a recently implemented method that endows solvent molecules with a parametric electron density, which exerts Pauli repulsion forces upon the solute. By applying the method to a set of aromatic molecules in solution we show that, for both polarizabilities and first hyperpolarizabilities, observed solution values are the result of a delicate balance between electrostatics, hydrogen-bonding, and non-electrostatic solute solvent interactions

On the nature of charge-transfer excitations for molecules in aqueous solution: a polarizable QM/MM study

We illustrate the effect of solvation on the nature of electronic excitations of organic molecules which possess excited states of charge-transfer character. The analysis is carried out using both a continuum model and a polarizable QM/MM method that treats the solvent atomistically and embeds each atom in the solvent with a fluctuating charge which responds to the solute quantum-mechanical electrostatic potential in a self-consistent manner. We also show how solvation dynamics can influence the nature of the excited state of molecular systems. The application of the model to aqueous solutions of doxorubicin and a substituted polythiophene derivative shows that the solvent significantly affects the nature the excited states, which results in an enhanced or reduced charge-transfer character as measured using two of the most popular indices for evaluating the distance traveled by the electrons upon excitation

Fully Polarizable QM/Fluctuating Charge Approach to Two-Photon Absorption of Aqueous Solutions

We present the extension of the quantum/classical polarizable fluctuating charge model to the calculation of single residues of quadratic response functions, as required for the computational modeling of two-photon absorption cross-sections. By virtue of a variational formulation of the quantum/classical polarizable coupling, we are able to exploit an atomic orbital-based quasienergy formalism to derive the additional coupling terms in the response equations. Our formalism can be extended to the calculation of arbitrary order response functions and their residues. The approach has been applied to the challenging problem of one- and two-photon spectra of rhodamine 6G (R6G) in aqueous solution. Solvent effects on one- and two-photon spectra of R6G in aqueous solution have been analyzed by considering three different approaches, from a continuum (QM/PCM) to two QM/MM models (non-polarizable QM/TIP3P and polarizable QM/FQ). Both QM/TIP3P and QM/FQ simulated OPA and TPA spectra show that the inclusion of discrete water solvent molecules is essential to increase the agreement between theory and experiment. QM/FQ has been shown to give the best agreement with experiments