Chairs
Professor Sir David C Clary FRS, University of Oxford, UK
Professor Sir David C Clary FRS, University of Oxford, UK
Sir David Clary is President of Magdalen College, Oxford and is Professor of Chemistry at the University of Oxford where he directs a research group working on the quantum theory of chemical reactions. He has held previous academic posts at Manchester, Cambridge and University College London. He has been President of the Faraday Division of the Royal Society of Chemistry and was the first Chief Scientific Adviser to the UK Foreign and Commonwealth Office. He is a Fellow of the Royal Society and was knighted in 2016 by the Queen for his services to international science.
09:00-09:30
Classical molecular dynamics simulations of electronically non-adiabatic processes
Professor William H Miller ForMemRS, University of California, Berkeley, USA
Abstract
A recently described symmetrical quasi-classical (SQC) windowing methodology for classical trajectory simulations has been applied to the Meyer-Miller (MM) model for the electronic degrees of freedom in electronically non-adiabatic dynamics. The approach treats nuclear and electronic degrees of freedom (DOF) equivalently (i.e., by classical mechanics, thereby retaining the simplicity of standard molecular dynamics), providing “quantization” of the electronic states through the symmetrical quasi-classical (SQC) windowing model. The approach is seen to be capable of treating extreme regimes of strong and weak coupling between the electronic states, as well as accurately describing coherence effects in the electronic DOF (including the de-coherence of such effects caused by coupling to the nuclear DOF). It is able to provide the full electronic density matrix from the one ensemble of trajectories, and the SQC windowing methodology correctly describes detailed balance (unlike the traditional Ehrenfest approach). Calculations can be (equivalently) carried out in the adiabatic or a diabatic representation of the electronic states, and most recently it has been shown that a modification of the canonical equations of motion in the adiabatic representation eliminates (without approximation) the need for second-derivative coupling terms.
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Professor William H Miller ForMemRS, University of California, Berkeley, USA
Professor William H Miller ForMemRS, University of California, Berkeley, USA
William H Miller was born in Kosciusko, Mississippi, in 1941, and grew up in Jackson. He received a BS in Chemistry from Georgia Tech (1963) and a PhD in Chemical Physics from Harvard (1967). During 1967-1969 he was a Junior Fellow in Harvard’s Society of Fellows, the first year of which was spent as a NATO postdoctoral fellow at the University of Freiburg, Germany. He joined the chemistry department of the University of California, Berkeley, as Assistant Professor in 1969 and has been Professor since 1974, serving as Department Chairman from 1989 to 1993 and becoming the Kenneth S Pitzer Distinguished Professor in 1999. Professor Miller has been elected to membership in the International Academy of Quantum Molecular Sciences (1985), the US National Academy of Sciences (1987), the American Academy of Arts and Sciences (1993), the Leopoldina (German National Academy of Sciences) (2011), and Foreign Member of the Royal Society (London) (2015).
09:45-10:15
When instantons get wet: path-integral rate theory for the condensed-phase
Dr Jeremy O Richardson, ETH Zurich, Switzerland
Abstract
Instanton theory results from a rigorous semiclassical derivation for the rate of a chemical reaction. However, due to a number of harmonic approximations, it is not applicable to study reactions in liquids, where many transition-states exist close to each other such that they cannot be treated independently. Ring-polymer molecular dynamics avoids this problem by effectively sampling the instantons without making the harmonic approximation. A similar instanton theory can also be derived for the rate of the fundamental process of electron transfer, in which the electron dynamics are coupled strongly to the nuclear degrees of freedom such that the Born-Oppenheimer approximation cannot be made. Again, however, this instanton theory cannot be applied to atomlistic models of liquids and a new ring-polymer sampling scheme is be required. It will be shown that starting from a physically motivated ansatz, it is possible to derive new ring-polymer sampling schemes which dominately sample the instanton configurations and thus give excellent approximations to the rate of electron transfer.
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Dr Jeremy O Richardson, ETH Zurich, Switzerland
Dr Jeremy O Richardson, ETH Zurich, Switzerland
Jeremy Richardson was born in Cardiff and studied at Cambridge University where he also took his PhD under the supervision of Stuart Althorpe. He was a postdoc and Humboldt Research Fellow in Friedrich-Alexander University Erlangen-Nürnberg in the group of Michael Thoss and a Junior Research Fellow at Durham University. In September 2016 he moved to ETH Zürich as the Assistant Professor of Theoretical Molecular Quantum Dynamics in the Laboratory of Physical Chemistry.
11:00-11:30
Quantum statistics with classical dynamics: applications to liquid water and ice
Professor Stuart C Althorpe, University of Cambridge, UK
Abstract
In water and ice, the nuclear motion takes place on a single Born-Oppenheimer surface, under conditions of thermal equilibrium. The nuclei exhibit quantum properties, which a growing body of evidence suggests are caused almost entirely by the quantum Boltzmann statistics, with the dynamics of the nuclei being classical. Here we summarise a recently developed theory which explains how such a classical dynamics can arise as a result of certain properties of the quantum statistics. This dynamics involves the motion of smooth delocalised loops of the hydrogen atoms which, despite being classical, conserve the quantum Boltzmann distribution. Exact implementation of this dynamics is not possible because of a phase problem, but its approximate implementation can be done using a ‘planetary’ model (originally developed heuristically by others), in which each hydrogen nucleus is represented by two particles, one (the ‘centroid’) describing its position, the other (the ‘planet’) describing the extent of delocalisation. We report recent simulations of the infrared spectrum of liquid water and ice, obtained using the planetary model. Despite the approximations made, the model is capable of reproducing the line shapes of the bend and stretch peaks, which are found to be motionally narrowed by the dynamics of the centroid.
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Professor Stuart C Althorpe, University of Cambridge, UK
Professor Stuart C Althorpe, University of Cambridge, UK
Stuart Althorpe obtained his PhD in Theoretical Chemistry from the University of Cambridge in 1994. After postdoctoral research in the US, Europe and Canada, he was awarded a Royal Society University Research Fellowship in 1999, which he held at Durham, Exeter and Nottingham. He returned to Cambridge in 2005, where he is now Professor of Theoretical Chemistry and Fellow of St Catharine's College. His research involves the development of new theory and methodology to better understand quantum effects in chemical dynamics. His current work focuses on the application of Feynman path-integral techniques to the dynamics of liquid water and chemical reactions.
11:45-12:15
Quantum nonadiabatic dynamics from classical trajectories
Professor Nandini Ananth, Cornell University, USA
Abstract
Simulating energy transfer pathways in reactions at metal surfaces requires methods that describe electronically nonadiabatic processes, capture quantum coherence effects, and remain computationally feasible for high dimensional systems. Quantum-limit semiclassical methods meet almost all these criteria, but the computational costs scale poorly with system size limiting their applications. The recently derived Mixed Quantum-Classical Initial Value Representation (MQCIVR) provides a uniform semiclassical framework for the calculation of real-time correlation functions where a subset of system modes are treated in the quantum limit while the rest are treated in the classical limit. This is achieved by selectively filtering amplitude of the semiclassical integrand in regions of highly oscillatory phase, leading to improved numerical convergence without significant loss of accuracy. This method is applied to several model systems and its ability to systematically tune individual system modes between quantum-limit and classical-limit semiclassical behaviour clearly demonstrated. MQC-IVR is further extended to electronically nonadiabatic processes for the study of inelastic scattering at a metal surface.
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Professor Nandini Ananth, Cornell University, USA
Professor Nandini Ananth, Cornell University, USA
Nandini Ananth received a PhD in Chemistry from the University of California, Berkeley, in 2008. Her thesis work was completed under the guidance of Professor William H Miller and focused on developing semiclassical methods for the simulation of quantum dynamic processes in complex chemical systems. Upon graduation, she accepted a position as postdoctoral scholar working with Professor Thomas F Miller III at the California Institute of Technology on developing path-integral methods for the simulation of electronically nonadiabatic processes in the condensed phase. She joined the faculty of the department of Chemistry and Chemical Biology at Cornell University in 2012, and during her time here has received various award including a Cottrell Scholar Award and Sloan Research Foundation Fellowship.