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SUMMARY:Second Harmonic Scattering: Atomistic Simulation and Machine Learn
 ing - Dr David M. Wilkins\, Laboratory of Computational Science and Modell
 ing\, EPFL
DTSTART:20180214T141500Z
DTEND:20180214T151500Z
UID:TALK101326@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:Recent second-harmonic scattering (SHS) experiments on electro
 lyte solutions have shown evidence of long-ranged intermolecular correlati
 ons between solvent molecules\, persisting on the ~10 nm length scale at s
 ub-molar concentrations\; SHS is extremely sensitive to these kinds of cor
 relations\, and an atomistic understanding of these complex experiments is
  desirable.\nI will discuss work in our group towards a computational fram
 ework for modelling SHS experiments of general condensed-phase systems. Fi
 rstly\, I will show that the orientational correlations between molecules 
 must be accounted for to fully model the SHS signal\, at variance with com
 mon assumptions.\nAccurate computational modelling of SHS experiments depe
 nds also on an accurate calculation of molecular hyperpolarizabilities: th
 is requires that we take into account the effects of environmental and (nu
 clear) quantum-mechanical fluctuations. The calculation of these response 
 tensors is computationally very demanding\, and I will describe a simple m
 achine-learning model that can sidestep these calculations for systems in 
 which a molecular axis system can be defined unambiguously.\nIn general sy
 stems\, this method will not work\, and so I discuss finally a framework t
 hat we have recently developed allowing for the prediction of any kind of 
 tensorial property by machine-learning\, taking into account the covarianc
 e of these properties under a rigid rotation. This method\, called symmetr
 y-adapted Gaussian process regression (SA-GPR)\, has the potential\, among
  many other applications\, to allow the simulation of light-scattering and
  spectroscopic experiments on general condensed phase systems\, without th
 e cost of quantum chemical methods.
LOCATION:Department of Chemistry\, Cambridge\, Unilever lecture theatre
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