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wales2_2015

Free energy landscapes and observation time scales

The analysis of energy landscapes is a powerful tool in modern theoretical chemistry, of particular use in structure prediction and the calculation of global thermodynamic and kinetic properties for systems of chemical, physical or biological interest. In order to compare the results of this theory with experiment, we should consider the effect of the time scale on which the experimental method views the system. The equilibrium free energy landscape that we usually study is not necessarily the same as the landscape probed by experimental measurements, because the system may only interconvert between locally stable conformations on a timescale longer than the temporal resolution of the experiment. The proposed project would be to investigate in detail the effects of incorporating this blurring of resolution into theoretical calculations. This approach promises to be insightful for comparison with experiments, but will also explore some interesting fundamental theoretical concepts, such as the connections between ergodicity (which may be broken on short observation timescales), symmetry and equilibrium. We will begin by studying the effect of timescales on the landscapes and rearrangement kinetics of colloidal clusters, for comparison with a new generation of optical microscopy experiments. The temporal and spatial resolution and data from such experiments is much higher than can typically be obtained for structural glass formers, where the question of time scale underpins much of the complex phenomenology. Hence the new insight gained into clusters of colloidal particles, with direct comparison of thermodynamic properties with experiment, should help to guide subsequent efforts to understand the glass transition.