Berlin 2018 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 49: Soft Matter Physics: Emerging Topics, New Instruments and Methods
CPP 49.4: Vortrag
Mittwoch, 14. März 2018, 15:45–16:00, C 230
Second-Harmonic Scattering: Theory and Atomistic Simulation — •David M. Wilkins1, Sylvie Roke2, and Michele Ceriotti1 — 1Laboratory of Computational Science and Modeling, IMX, EPFL, Lausanne, Switzerland — 2Laboratory for fundamental BioPhotonics, Institutes of Bioengineering and Materials Science and Engineering, School of Engineering, and Lausanne Centre for Ultrafast Science, EPFL, Lausanne, Switzerland
Recent second-harmonic scattering (SHS) experiments on electrolyte solutions have shown evidence of long-ranged ion-induced intermolecular correlations between solvent molecules, persisting on the ∼10 nm length scale at sub-molar concentrations. SHS is exquisitely sensitive to these subtle structural changes, and an atomistic understanding of the kinds of correlations probed is desirable.
I discuss the development of a computational framework for modelling SHS experiments of general condensed-phase systems. This includes two main ingredients: firstly, the orientational correlations between molecules, and secondly, the molecular hyperpolarizability tensor. I show that, at variance with common assumptions, even in an isotropic liquid the modelling of the SHS signal requires that correlations be accounted for, and that the hyperpolarizability tensor depends strongly on the molecular environment. Further, I discuss a machine-learning framework we have developed to sidestep computationally expensive calculations of this tensor, which provides a large step towards the routine calculation of SHS intensities of general systems using machine-learning methods.