Supercomputer modelling of advanced materials

The potential energy landscape provides a conceptual and computational framework for investigating structure, dynamics and thermodynamics in condensed matter and molecular science. This talk will summarise new approaches for global optimisation, calculating thermodynamic properties in systems exhibiting broken ergodicity, and rare event dynamics. Applications will be presented that exploit generalised basin-hopping for global optimisation in continuous and discrete metric spaces, with examples ranging from biomolecules tomachine learning and quantum computing. Design principles for self-assembly of mesoscopic structures extend the single funnel paradigm to multifunnel landscapes, with the potential for encoding multifunctional materials.

Selected Publications:

DJ Wales, Annu Rev Phys Chem (2018) 69, 401

JA Joseph, K Röder, D Chakraborty, RG Mantell, and DJ Wales, Chem Comm 53, 6974, 2017.

DJ Wales, "Energy Landscapes", Cambridge University Press, Cambridge, 2003

Professor David J Wales FRS, University of Cambridge, UK

Professor David J Wales FRS, University of Cambridge, UK

David J Wales received his BA degree from Cambridge University in 1985 and his PhD in 1988 under the supervision of Professor AJ Stone. He was awarded the ScD degree in 2004.  He spent 1989 as a Lindemann Trust Fellow at the University of Chicago, working with Professor RS Berry. He returned to a Research Fellowship at Downing College Cambridge in 1990, was a Lloyd's of London Tercentenary Fellow in 1991, and a Royal Society University Research Fellow from 1991 to 1998. In 1998 he was appointed to a Lectureship in Cambridge and is now Professor of Chemical Physics. He was awarded the Meldola Medal and Prize in 1992 by the Royal Society of Chemistry, and the Tilden Prize in 2015. He was a Baker Lecturer at Cornell University in 2005, and the Inaugural Henry Frank Lecturer at Pittsburgh University in 2007.  His research primarily involves the exploration of potential energy landscapes, with applications to chemical biology, spectroscopy, clusters, solids and surfaces.

New chemical materials and compounds serve as the foundation for the modern technology of our civilisation, where these materials should be environmentally friendly, with stable and controllable properties for a multitude of applications, and at the same time energy efficient in their synthesis. Traditionally, such materials are generated in bulk and then machined down to whatever size is needed. But such materials are also often grown in a bottom-up approach on a substrate, and in the extreme we are dealing with and aiming for low-dimensional systems with bespoke properties, where the stability of such materials often becomes an issue of concern. Among these systems, we find monolayers on surfaces or inside layered compounds, ultrathin films, nanotubes and nanowires, just to name a few, which are becoming increasingly important from a technological point of view. The ability to predict such kinetically stable and/or thermodynamically (meta)stable nanomaterials, followed by a computation of their properties and evaluation of their stability, is clearly of great value in their design and synthesis.[1] For the past three decades, the structure prediction of three-dimensional bulk crystalline compounds and their modifications[1,2] on the one hand, and of single atom clusters[3] and (bio)molecules[4] on the other hand, has shown great progress, and the computational approaches used are expected to be also applicable to low-dimensional systems.[5,6] In this presentation, Professor Schön will discuss the methodological features specific to the prediction of the latter systems,[7] together with examples of structure prediction for one-dimensional (eg, atom chains),[7] quasi-one-dimensional (eg, nanotubes),[7] two-dimensional (eg, monolayers),[5,8] quasi-two-dimensional (eg, layer-like building blocks for layered compounds),[9] and composite (eg, multi-molecule patterns on substrates)[10] systems.

[1] JC Schön, M Jansen, Angew. Chem Int Ed, 35:1286 (1996)
[2] SM Woodley, CRA Catlow, Nature Mater, 7:937 (2008)
[3] DJ Wales, H Scheraga, Science, 285:1368 (1999)
[4] GM Day et al, Acta Cryst B, 61:511 (2005)
[5] JC Schön, Process Appl Ceram, 9:157 (2015)
[6] SM Woodley, GM Day, CRA Catlow, Phil Trans Royal  Soc A, 378:20190600 (2020)
[7] JC Schön, in: Energy landscapes of nanoscale systems, Ed: DJ Wales, chapter 12 (Elsevier, Amsterdam, 2022)
[8] R Gutzler, JC Schön, Z Anorg Allg Chem, 643:1368 (2017)
[9] A Mahmoodabadi, M Modarresi, JC Schön, in preparation
[10] S Abb et al, Angew Chem Int Ed, 58:8336 (2019)

Professor J Christian Schoen, Max-Planck-Institute for Solid State Research, Germany

Professor J Christian Schoen, Max-Planck-Institute for Solid State Research, Germany

J Christian Schön studied physics at Bonn University and at MIT, where he received his PhD in theoretical solid state physics in 1988. Subsequently, he was Postdoc in mathematics at SDSU in San Diego, in physics at the Universities of Odense and Copenhagen, and in chemistry at Bonn University, where he became apl Professor in 2008. He is a Fellow of the Royal Society of Chemistry. Since 1999, he has been a Senior Scientist at the Max Planck Institute for Solid State Research. His main research areas are the theory of complex multi-minima-energy landscapes and their application in chemistry, such as prediction and modeling of molecular structures and clusters in vacuum and on surfaces, of metastable crystalline and amorphous materials in 1 - 3 dimensions, and the simulation and optimisation of their synthesis, employing techniques from the area of global optimisation, MC and MD simulations, optimal control and finite-time thermodynamics.

Controlling the formation of specific polymorphs during crystallisation is of great interest in the design of materials with specific properties. However, the initial stages of nucleation and growth during solidification are still not fully understood, even for seemingly simple systems such as unary metals. Using transition path sampling, the researchers have studied the microscopic mechanisms during homogeneous nucleation in nickel. Their analysis of the path ensemble reveals that the emergence of the crystalline phase is preceded by the formation of pre-structured regions in the liquid that act as precursors. Extending their study to heterogeneous nucleation, they likewise observe a precursor-mediated crystallisation mechanism. Small seeds impact the structural characteristics of the liquid and induce the formation of precursors with specific structural hallmarks. The nucleating ability and polymorph selectivity of these templates is, therefore, not simply given by lattice mismatch and translational order but strongly linked to the seed’s ability to promote the formation of suitable precursors in the liquid. Furthermore, they have analysed the dynamical heterogeneity in the liquid which is revealed to play a key role in the nucleation mechanism. Crystallisation occurs preferentially in regions of low mobility in the supercooled liquid. These low mobility regions form before and spatially overlap with the regions of structural precursors, revealing a clear link between dynamical and structural heterogeneity in the liquid. The relationship between structural and dynamical heterogeneity in the liquid and the nucleation mechanism appears to be key in controlling essential parameters during crystallisation, including nucleation rates and polymorph selectivity. 

Dr Jutta Rogal, New York University, USA

Dr Jutta Rogal, New York University, USA

Jutta Rogal is currently a Heisenberg Fellow of the German Research Foundation with a research appointment at the Department of Chemistry at New York University (NYU) and the Department of Physics at Freie Universität Berlin (FUB). She received her doctorate from FUB in 2006, carrying out her PhD work on electronic structure calculations for surface catalysis at the Fritz Haber Institute. For her PhD thesis, she was awarded the Otto Hahn Medal of the Max Planck Society and the Ernst-Reuter Preis of the FUB. In 2007, Jutta moved to the University of Amsterdam as a Postdoctoral Researcher to develop methodological extensions to the transition path sampling approach, before joining the Interdisciplinary Centre for Advanced Materials Simulation at the Ruhr University Bochum as Group Leader from 2009-2020.  In 2016, she was awarded a Feodor Lynen Research Fellowship of the Alexander von Humboldt Foundation which she spent at NYU in 2017/18 working on enhanced sampling techniques for high-dimensional energy landscapes. 

The delivery of the next generation of medical treatments such as regenerative medicine hinges on our ability to store biological material. Cryopreservation - that is, the process of freezing biological material whilst retaining its function - is our best bet to achieve that, but the state-of-the-art suffers from a number of crippling limitations. One such limitation is the rather scanty portfolio of cryoprotectants available to us: these compounds are added into the mix so as to control the formation of ice in biological matter and thus mitigate the many detrimental effects caused to cells and tissues by the growth of ice crystals. We need more effective, safer, less toxic, cheaper cryoprotectants - and yet, in the last few decades we have failed to design any valid alternative to the very few compounds (glycerol being a prominent example) that we have more or less serendipitously discovered in the by now distant past. This is because we lack the molecular-level understanding of how exactly cryoprotectants work. In this talk,  Dr Sosso will present some recent advances specific to the mechanism of ice re-crystallisation inhibition agents, ie compounds that limit the growth of ice crystals - one of the many aspects that a cryoprotectant can act upon. In particular, Dr Sosso will discuss the picture emerging from our findings in terms of the ice re-crystallisation inhibition activity of selected polymers, peptides and surprisingly small molecules as well. Whilst the ultimate goal of achieving the rational design of novel cryoprotectants might still be beyond our grasp, molecular simulations are playing an important part in getting us all there - and, the further we progress, the greater the computational demands that we will need to meet. 

Dr Gabriele C Sosso, University of Warwick, UK

Dr Gabriele C Sosso, University of Warwick, UK

Gabriele C Sosso is an Associate Professor in Computational Physical Chemistry at the University of Warwick. He obtained his PhD in Nanostructures and Nanotechnologies from the University of Milano-Bicocca (Italy) in 2012, under the supervision of Professor Marco Bernasconi. He has worked as a PostDoctoral Research Associate with Professor Michele Parrinello at ETH Zürich and with Professor Angelos Michaelides at UCL. Gabriele is a computational scientist, chiefly interested in the physical chemistry of condensed matter, from supercooled liquids to biological interfaces. His vision is to understand the functional properties and the phase transitions of different classes of systems, from metallic glasses to cellular membranes. His approach consists in performing fundamental research using computer simulations, aimed at rationalise, complement and guide experiments and applications. Particularly relevant in the context of this meeting is Gabriele’s work on crystal nucleation and growth, which encompasses large-scale, machine learning-based simulations of semiconducting materials as well as enhanced sampling simulations of water freezing into ice at complex interfaces.

Ion binding at surfaces from solution is an important process in a variety of contexts from geochemistry through to the crystallisation of materials. Therefore, knowledge of the thermodynamics of such events is vital for predicting how systems will grow or dissolve under a set of conditions. With the advent of supercomputers and enhanced sampling methods, the determination of free energies for such adsorption processes is becoming increasingly possible, even for water where solvent exchange rates can be slow on the molecular dynamics timescale. Although numerous examples of solid-solution ion transfer can already be found in the literature, especially based on pathway-driven techniques, such as metadynamics or umbrella sampling, this presentation will examine the question of whether such information is actually meaningful or useful in the form often given? To explore the above question, this talk will focus on the widely studied example of NaCl growth from aqueous solution. Specifically, Professor Gale will consider the free energies of the kink sites relative to aqueous solution, as the correctness of the thermodynamics can be readily checked via the bulk solubility. By comparing the free energies of these sites as determined by a range of approaches, including pathway or alchemical techniques, it will be shown that wildly varying answers can be arrived at. However, after careful correction for all relevant simulation factors, such as system size and state, it will be shown that consistent and valid results can be reached by both alchemy and pathway-based methods.

Professor Julian Gale, Curtin University, Australia

Professor Julian Gale, Curtin University, Australia

Professor Julian Gale obtained his first degree from the University of Oxford in Natural Sciences (Chemistry), where he continued on to study for a DPhil in the Department of Chemical Crystallography. After a postdoctoral position at the Royal Institution of Great Britain he moved to Imperial College London as a Royal Society University Research Fellow and subsequently Reader in Theoretical and Computational Chemistry. In 2003, he moved to his current location, Curtin University, as a Premier’s Research Fellow and now holds the position of John Curtin Distinguished Professor of Computational Chemistry. Recently he was awarded an Australian Research Council Laureate Fellowship and is a Fellow of the Australian Academy of Science. Research interests include the development and application of computational techniques to problems in areas including materials chemistry, crystallisation, geochemistry and mineralogy.