Posted on09/03/2021byAgeo Meier de Andrade|Comments Off on Supercooled liquid-like dynamics in water near a fully hydrated titania surface: Decoupling of rotational and translational diffusion
Authors: Lorenzo Agosta, Mikhail Dzugutov, and Kersti Hermansson
We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO2 on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation–translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation–translation decoupling in an ab initio MD simulation of water.
The adversities with covid-19 also brought the chance to re-think how conferences could still happen worldwide. It was not different from the 2020 eSSENCE Multiscale modelling of molecules in materials meeting on the 8th of June this year, the first time the conference was broadcasted to 599 registered participants from 51 countries in all continents.
From a conventional conference to a modern webinar
Kersti Hermansson, Professor in Inorganic Chemistry at Uppsala University and the main conference organizer, shared what kind of decisions were needed to make the conference happen. Kersti: “In the midst of our planning for the June 2020 meeting, the consequences of the Corona pandemic hit us, and we had to decide whether to postpone, skip or pursue the conference plans. After some deliberation we opted for the latter, checked the willingness of the speakers to switch to webinar mode, sent out a new set of announcements to all the forums already contacted, and – most of all –we had to learn all the technical bits and pieces needed to run a smooth online meeting, which was totally new to all members of our research group”.
Professor Hermansson emphasizes the wish to arrange the conference with high interaction from the participants. “Overall, our philosophy was to make the online conference as similar as possible to our “normal” eSSENCE conferences in previous years. That is, we wanted to try to include all the same scientific ingredients as usual: keynote presentations of international authorities, invited talks, a presentation from the eSSENCE coordinator, poster session, panel discussion, vivid discussions, and the conference was as usual run from the Siegbahn Hall at the Ångström Laboratory, now with 15 sparse participants on-site to create the “ambiance” of an IRL meeting.
The participants were from all over the globe, from both industry and universities
Over 210 academic institutions and 78 companies were represented at the conference. Among industrial participation, which accounted for 20% of the registered participants, companies such as Johson Matthey, Dassault Systemes, BIOVIA, AstraZeneca, Northvolt AB and many others were active during the scientific discussions, the poster session and panel discussion. The eSSENCE multiscale modelling meeting has built up some national recognition over the years, as evidenced by broad participation over the country. This year’s Swedish participation came from eSSENCE, from SeRC (SU, KTH, LiU), from e-science communities at CTH and GU, as well as from Högskolan in Gävle, Malmö Högskola, Örebro University and the Technical University of Luleå. As usual, eSSENCE@Lund was much supportive in the planning, and Magnus Ullner (LU) also took part in the implementation of the panel discussion.
The eSSENCE of complex systems
The conference’s main scientific topic in 2020 was “Multiscale modelling of materials and molecules ? in complex systems”, with the overall focus on methods and model development. The computational aspects of two large new European programmes were highlighted in the programme. Multiscale modelling in battery research was the topic of the first keynote lecture given by Professor Tejs Vegge from the Technical University of Denmark, one of Battery 2030+ research initiative leaders. Data-driven approaches of multiscale modelling were the main topic of the other two keynote lectures. Professor Anatole von Lilienfeld from the University of Base discussed the scientific community’s efforts on coupling data science, alchemy, and quantum machine learning. Professor Peter Coveney from University College London gave a fascinating lecture entitled “Big data: The end of the scientific method?” With the notable success of the conference, the organizers plan to keep the digital format for 2021. The organizers plan a 2-day conference, and a limited number of in-person attendance is being considered. Stay tuned for more information!
Authors: Yocefu Hattori, Jie Meng, Kaibo Zheng, Ageo Meier de Andrade, Jolla Kullgren, Peter Broqvist, Peter Nordlander, and Jacinto Sá
Plasmonic materials have optical cross sections that exceed by 10-fold their geometric sizes, making them uniquely suitable to convert light into electrical charges. Harvesting plasmon-generated hot carriers is of interest for the broad fields of photovoltaics and photocatalysis; however, their direct utilization is limited by their ultrafast thermalization in metals. To prolong the lifetime of hot carriers, one can place acceptor materials, such as semiconductors, in direct contact with the plasmonic system. Herein, we report the effect of operating temperature on hot electron generation and transfer to a suitable semiconductor. We found that an increase in the operation temperature improves hot electron harvesting in a plasmonic semiconductor hybrid system, contrasting what is observed on photodriven processes in nonplasmonic systems. The effect appears to be related to an enhancement in hot carrier generation due to phonon coupling. This discovery provides a new strategy for optimization of photodriven energy production and chemical synthesis.
Nano Lett. 2021, 21, 2, 1083–1089 https://doi.org/10.1021/acs.nanolett.0c04419
Posted on14/12/2020byAgeo Meier de Andrade|Comments Off on Lignin Intermediates on Palladium: Insights into Keto‐Enol Tautomerization from Theoretical Modelling
Authors: Ageo Meier de Andrade, Pemikar Srifa, Peter Broqvist, and Kersti Hermansson
It has been suggested in the literature that keto‐to‐enol tautomerization plays a vital role for lignin fragmentation under mild conditions. On the other hand, previous modelling has shown that the adsorbed keto form is more stable than enol on the Pd(111) catalyst. The current density functional theory study of lignin model molecules shows that, in the gas‐phase, keto is more stable than enol, but on the Pd surface, we find enol conformers that are at least as stable as keto. This supports the experimental result that the favourable reaction pathway for lignin depolymerization involves keto‐enol tautomerization. An energy decomposition analysis gives insights concerning the origin of the fine energy balance between the keto and enol forms, where the molecule–surface interaction (−7 eV) and the molecular strain energy (+3 eV) are the main contributors to the adsorption energy.
************************************************************ The 2019 eSSENCE meeting on “Multiscale modelling of materials and molecules” will take place 3-5 June in Uppsala https://sites.google.com/site/emultiscale2019/
“The Nanoporous Materials Genome in action – molecules in prison.”
“Molecular property = f(structure) relations from QSAR, physics and ML”
“Technology buzzwords in Silicon Valley – and what they mean.”
“Probabilistic modelling – driven by data, guided by physics”
“The road to accuracy – and how to assess it.”
“Multiscale-modelling of batteries and Battery 2030+”
… and more to come!
The meeting will have a continued focus on the challenge of physics-based and data-driven?” How can physics-based insight and data-driven analysis best work together (or at least how can they complement each other)? Will the reliability and accuracy of our results improve?Registration is open! Abstracts on the general theme of multiscale modelling (we use the term in a broad sense) and on the data-driven vs. physics models theme are equally welcome.
Very welcome to come and participate and discuss modelling!
Posted on12/05/2018byPavlin Mitev|Comments Off on Seminar: “Mineral/water interfaces characterized by Ab Initio Molecular Dynamics: making the link between structure and SFG vibrational spectroscopy”
Time: Thursday 17 May 2018 at 14.15 Room: Å 4001
Title: “Mineral/water interfaces characterized by Ab Initio Molecular Dynamics: making the link between structure and SFG vibrational spectroscopy”
Speaker: Professor Marie-Pierre Gaigeot
LAMBE UMR 8587, Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, Université d’Evry val d’Essonne, Paris – Université Paris Saclay, France, firstname.lastname@example.org
In this presentation, we will review our recent theoretical works on the characterization of mineral/liquid water interfaces, i.e. silica/water (crystalline and amorphous) and alumina/water interfaces, making the link between structure and non-linear SFG (Sum Frequency Generation) experiments. Non-linear SFG spectroscopy in the 3000-4000 cm-1 spectral domain is indeed one method of choice to probe complex inhomogeneous solid/liquid and liquid/air interfaces. Although an extremely powerful technique, the detailed interpretation of the experimental signatures requires associated calculations. This is the challenge we have been tackling over the past 5 years, applying Ab Initio DFT-based molecular dynamics simulations (DFT-MD).
I will illustrate here some of our recent works showing how to separate vibrational signatures arising from the different layers of water at the interface, how to provide a direct interpretation of the H-Bond networks at play at interfaces (water-water vs solid-water networks), including our recent works unraveling 2-dimensional interfacial water networks, how to define the only three spatial regions of interest at any charged interfaces (BIL, Binding Interfacial Layer; DL, Diffuse Layer; Bulk) and how to universally interpret/assign SFG vibrational bands from these three regions, including χ2 and χ3 contributions into the theoretical signals. We will also show how our deconvolution schemes for SFG spectral interpretation provide direct knowledge of the isoelectric point at any aqueous surface and direct knowledge of the formation of an Electric Double Layer (EDL) when aqueous ionic solutions are considered at the interface. We will unravel trends in going from hydrophobic to hydrophilic surfaces at the interface with liquid water.
Acknowledgments: Collaborative works with Prof. Y. Ron Shen at the University of California at Berkeley, USA, Prof E. Borguet at Temple University, USA, Dr E. Backus, Max Planck Institute in Mainz, Germany. Works achieved with PhD/Post-Doc students S. Pezzotti, D. Galimberti, M. Pfeiffer-Laplaud, L. Potier, F. Siro Brigiano, A. Cimas.
************************************************************ The 2018 eSSENCE meeting on “Multiscale modelling of materials and molecules” will take place 11-13 June in Uppsala https://sites.google.com/site/emultiscale2018/
A special feature of this meeting will be the focussed workshop on the theme
“Materials and molecular modelling in the 21st century: Physics-based or data-driven?”
Researchers in computational chemistry, physics and biology traditionally use physics-based* models. However, currently there is much excitement (to use a mild word) about big data and machine learning in materials and molecular modelling, and the opportunities that these approaches can bring. But are there scientific risks and shortcomings coming with it? Is this development in fact driving us towards “…numbers, not insights”, i.e. away from Professor Charles Coulson’s (Oxford) famous wish for “…insights, not numbers” ?!
Together with local and international experts from the NOMAD (European Center of Excellence; www.nomad-coe.eu ) and AiiDA (www.aiida.net) initiatives and the Virtual Fab multiscale-platform (South Korea; nano.vfab.org) all participants are welcome to join in enlightening these multi-facetted questions through presentations and discussions.
The seminar in the series “The eSSENCE of COMPUTATIONAL CHEMISTRY&PHYSICS” took place Wednesday 28 March.
Title: “Molecular dynamics of the challenging OH* radical in aqueous environments”
Speaker: Professor Peter G Kusalik, University of Calgary, Alberta, Canada
Place: Ångström, Beurlingrummet
Abstract: This talk deals with the computer exploration of structure, mobility and reactivity of hydroxyl radical (OH*) in aqueous environments. Results from direct simulations, from constrained and metadynamics, and from gas phase benchmarking calculations will be presented. Implications for effective potentials for modeling OH* in aqueous environments will also be discussed.
The behaviour of OH* in aqueous environments is crucial to its role in various important reactions within or at the surfaces of water and ice. The OH* is a key chemical species that appears across a diverse range of fields such as atmospheric chemistry, cosmic and nuclear reactions, and the biomolecular mechanisms of aging and diseases such as cancer, for example. OH* has proven to be a very challenging species to investigate because of its highly reactive nature. Here I will report insights into the behaviour of the hydroxyl radical in water and in ice through, primarily, Car-Parrinello molecular dynamics simulations.
The reactivity, stability and mobility of OH*, and its relationship to local structure, will be discussed. I will demonstrate that the hydrogen atom transfer between OH* and a water molecule has a relatively small free energy barrier and follows an apparent hybrid (electron-proton transfer) mechanism in which local structural fluctuations play an important role. Details of the reactions and interactions that can occur between two OH* in water will be presented, where the production of an aqueous oxygen atom, O(aq), in the triplet state is observed. I will also show that two-center three-electron (“hemi-bond”) interactions play a crucial role in the behaviour of OH* in water and ice, particularly when there is a constrained hydrogen-bonding environment.
Kersti Hermansson and Peter Broqvist. Structural Chemistry, Ångström