V Coloquio de Simulaciones Computacionales en Ciencias

Density functional theory to probe hydrogen diffusion on, into and in magnesium

– Marina Shelyapina – Saint Petersburg State University

Resumen

Hydrogen is an energy carrier that can become a sustainable solution for alternative energy with zero greenhouse gas emissions. Hydrogen storage is a key point for hydrogen energy. Metals provide access for safe, controlled and reversible storage and release of hydrogen. Magnesium, due to its high hydrogen storage capacity, high natural abundance, low cost and non-toxicity, is one of the most attractive hydrogen storage materials. The efficiency of magnesium as a hydrogen accumulator is limited by its slow hydrogen sorption kinetics and the high stability of its MgH2 hydride. Many efforts have been made to overcome these drawbacks. At the microscopic level, the absorption of hydrogen by metal is a complex multi-stage process that cannot be followed experimentally. Theoretical studies help clarify this process and focus experimental efforts on the development of new efficient Mg-based materials for hydrogen storage. This lecture provides a review of the results obtained within the framework of the density functional theory approach to studying interactions of hydrogen with magnesium surfaces, diffusion of hydrogen on Mg surfaces, inside and in Mg bulk, as well as phase transformations caused by hydrogen in MgHx, and hydrogen desorption from MgH2 surfaces.

Simulation vs understanding: A tension, and not just in our profession 

– Roald Hoffmann – Cornell University

Abstract

At times it feels like there is a wave, crashing down on us, and not just
in our field, quantum chemistry. The wave is driven by information technology; its
arms are machine learning, neural networks, and artificial intelligence. Soon
quantum computers are going to bring us exact numerical solutions to equations
which we have been struggling to solve. But those numbers — now hard-won, soon
easy to get — will provide close to zero understanding. To justify this provocative
statement, we need to define understanding, a jewel of human thought for
centuries. The ability to form explanations, to teach a student, play an important
part of the definition.
In this lecture, based on three essays with Jean-Paul Malrieu, we will move
from the words, and philosophical ideas around them, to the practical way in which
simulation interacts with experiment today. I will describe the feeling of being
beaten by computers, not just in playing chess or go, but in the process of
searching for a new chemical structure, The tension between simulation and
understanding is there, of course, not only in chemistry – I will give examples of
from economics, commerce, and “big data.” There are deep moral implications of
AI and IT for all of us. No solutions at the end, just a recognition of the problem,
and a plea to stay human. Chemistry’s streak of creation provides in that conjoined
future a passage to art and to perceiving, as Jean-Paul and I argue, the sacred in
science.

Mis inicios en cálculos ab initio

– Armando Reyes Serrato – Centro de Nanociencias y Nanotecnología, UNAM

Resumen

Presentaré resultados de algunos trabajos de investigación de estructura electrónica y propiedades de materiales, que fueron obtenidos en colaboración con el Dr. Donald Homero Galván Martínez. Hablaré primero de como terminé en el área de Cómputo Científico apoyado por el Dr. Galván, siendo que mi proyecto de tesis doctoral inicial pertenecía completamente al área experimental. Comentaré sobre la idea inicial del Laboratorio Virtual de Materiales, misma que finalmente culmina con la creación del Departamento de Modelación de Nanomateriales del Centro de Nanociencias y Nanotecnología de la UNAM. Finalmente describiré el actual enfoque del Laboratorio Virtual para el análisis de
los Materiales Cuánticos Topológicos.

Lo que fue, lo que es, lo que será. Amistad, cooperación, recuerdos.

–Vitalii Petranovskii – Centro de Nanociencias y Nanotecnología, UNAM

Resumen

Nuestro triste derecho a recordar para siempre a quienes han estado con nosotros todos estos años y cuya existencia fue parte de la cotidianidad, tan natural como respirar, como el aire. Al interactuar con los demás, buscamos la comprensión, sin la cual es triste vivir, y con la cual nuestro ser se vuelve hermoso. Tendemos a buscar no solo el conocimiento experto, sino también la calidad humana en nuestro interlocutor y colaborador. Homero se distinguía por una característica que hacía que trabajar con él fuera un gran placer: cuando discutía las características de la formación de un enlace químico en una estructura, veía un átomo bien definido detrás de cada línea de una ecuación abstracta; su capa de electrones; la simetría de sus electrones constituyentes; los conocía "de vista", y tenía en cuenta las peculiaridades de sus caracteres; distribución de estos electrones; y pudo explicar sus ideas con claridad. Y también formular claramente la tarea del algoritmo computacional de un programa de computadora, y luego convertir números secos en una historia animada y fácilmente comprensible sobre el comportamiento de electrones, átomos, iones, cúmulos. Sobre las nanopartículas que construyen el mundo que nos rodea.

Density-Functional Theory of Aqueous Systems From the Dimer to the Thermodynamic Limit:
Lessons from a Many-Body Formalism

–Etienne I. Palos – University of California, San Diego.

Resumen

Given its anomalous physical properties and its importance to life, water is one of the most studied molecules. From a modeling perspective, there is growing interest in developing a purely predictive framework that enables the description of water and therefore aqueous-phase chemistry. However, developing such a framework is challenging due to (i) the interplay between many-body (MB) interactions and the spatial arrangement of the hydrogen-bond network that defines the structure of liquid water, and (ii) the computational cost of quantum chemical methods capable of accurately describing MB interactions. Recently, we developed a general framework for the derivation of many-body potential energy functions (MB PEFs) from arbitrary levels of theory; including density-functional theories (DFT) and post-Hartree-Fock wave-function theories. Due to the 30-year history of Kohn-Sham DFT modeling of water, with no density functional approximation (DFA) shown to reproduce the physical properties of water from the gas to the condensed phase, we paid close attention to Density Functional Theory (DFT)-based data-driven MB PEFs for water, described as MB-DFT. We learned that the interplay between density-driven and functional-driven errors can hinder the transferability of accuracy from Kohn-Sham DFT to the data-driven MB-DFT models, with respect to the gas phase. This is particularly apparent in semi-local functionals that have high delocalization and self-interaction error.

Subsequently, through the definition of a density-corrected many-body formalism, we demonstrated that the accuracy of density functional theory (DFT) for water can be improved significantly. Building upon these studies, we investigate here systematic errors in semi-local DFT models, and their implications for accurate representations of water, through a many-body analysis. Our analyses show that DC-SCAN effectively predicts the gas phase energetics of water at coupled-cluster accuracy, and that this acquired accuracy is preserved in MB-SCAN(DC) for water.

Finally, we apply our framework to DeepMind 21 (DM21), a deep-learned functional that effectively reproduces the piecewise linear behavior of the exact energy functional as a function of fractional charge. Beyond analyzing neutral, protonated and deprotonated water clusters using DM21, we present the MB-DM21 PEF and perform many-body molecular dynamics simulations, demonstrating DM21 lacks predictive capabilities in reproducing the properties of liquid water and aqueous systems. While this talk is centered on water, we believe that our findings unveil fundamental relations between the shortcomings of DFT and implications for accurate descriptions of molecular interactions in N-body systems, representing progress toward a unified framework for condensed phase simulations.

“Homero Galvan: el entrañable amigo y compañero de trabajo”

– Miguel Avalos Borja – Instituto Potosino de Investigación Científica y Tecnológica, A.C. 

Resumen

E

Familia del Prof. Galván

Cierre LVMM