Combining multi-scale simulation and scattering for structural analysis of complex systems
CECAM-HQ-EPFL, Lausanne, Switzerland
Atomistic simulation is increasingly being used to interpret small angle and total scattering data in disordered and soft matter systems. The method allows introduction of known constraints (e.g. molecular geometry and interaction energies) into the structure determination and refinement, and give as output an atomistically detailed structural ensemble consistent with the data. Two key examples include Empirical Potential Structure Refinement (EPSR)  and its application to the interrogation of liquid and amorphous systems utilising total neutron and X-ray scattering data, and SASSIE for calculations of SAXS/SANS from biological molecules in solution [2,3]. These tools, and other similar methods  have yielded a large volume very high quality science in a wide number of fields. In particular, EPSR has transformed structure determination in molecular liquids and allowed the study of increasingly complex and varied systems [5,6,7].
The recent developments of wide Q-range neutron scattering instruments (e.g. NIMROD at ISIS (UK) and NOVA and TAIKAN at J-PARC(Japan)) and the enhanced availability of combined SAXS/WAXS at both synchrotrons and as lab sources, increasingly mean that both atomistic and mesoscale structures can be investigated simultaneously. Furthermore, there is a push to study ever more complex and applied systems e.g. large surfactant micelles, polymer conjugates and heterogeneous systems. These trends mean that computational and methodological limits are frequently being met, particularly when both atomistic and mesoscale structure need to be understood together. This workshop will bring together experts from the neutron scattering and simulation communities, with experience of a variety of different systems and techniques, in order to explore new methods that will drive forward the interpretation and refinement of scattering data across the multiple length scales probed by the current, and indeed the next, generation of instrumentation.
Potential methods to explore include the use of Coarse-Grained (CG) simulation , multi-box simulation (i.e. many simulations representing parts of the system that are recombined to form the total structure factor), simulation constrained by SAXS/SANS data fitting and Bayesian or machine learning approaches. The development of these techniques in the present context, however, is in its infancy, with a number of open problems remaining: How to simultaneously refine simulations at different length-scales? How to efficiently calculate scattering from CG simulations? Which are the most appropriate methods for mapping atomistic structures to coarse grained ones? What level of coarse-graining is appropriate for a system? Can additional measurements be added into the refinement the structure? This timely workshop will bring together experts in these emerging techniques with the aim of building a community working towards a set of solutions for structural understanding of multiscale systems from scattering experiments.
Thomas Headen (Science and Technology Facilities Council) - Organiser
Guadalupe Jimenez Serratos (Imperial College London) - Organiser
Erich Muller (Imperial College London) - Organiser
Tristan Youngs (STFC) - Organiser