The Alumni Talks are organized by the Young Research Parlament of the Hylleraas Center.
Speaker: Hima Bindu Kolli
Title: Multiscale Simulation Scattering Intensity Calculator (MuSSIC): Validation and Application to Soft-Matter Systems
Abstract: The combined use of neutron scattering experiments with molecular simulation is increasingly being utilised to study multiscale structures in molecular biology and soft matter science [1-4]. Despite the progress in the methods and force fields in all-atom models, sufficient sampling is computationally expensive for micellar systems like CTAB surfactants, due to the large time and length scales involved in the aggregation dynamics [3]. Furthermore, Small-Angle Neutron Scattering (SANS) can provide data at hundreds of nanometres length scale, atleast an order of magnitude larger compared to the typical atomistic simulation. For such systems, coarse grain (CG) models are often utilised to reduce computational cost and to explore the global structures at larger length scale. Following a preliminary study [Soper and Edler, Biochimica et biophysica acta, 2017, 1861, 6], the neutron-weighted total structure factor, FCG(Q), has been compared to those obtained from atomistic simulations of polyamide-66 and a concentrated solution of C10TAB surfactant in water. We implemented a novel method for obtaining the scattering curves for pseudo-CG trajectories, which are compared to the atomistic benchmark calculations with the same underlying structure. Our results show excellent agreement between the atomistic and CG curves in the low Q region, with differences apparent at higher Q due to the loss of resolution. We demonstrate the scientific usefulness and understanding provided by the code, by comparison of CG simulations to the experimental scattering data for archetypal soft matter systems, SDS and CTAB solutions. We were able to use the marked differences with experimental SANS data to give a detailed understanding of the appropriateness of the CG simulation methodologies used for predicting structure. This forms a first step towards new approaches in SANS data analysis, particularly in allowing refinement of models against one or more experimental data sources.
References
1. Max C. Watson and Joseph E. Curtis, J. Appl. Cryst. (2013). 46, 1171–1177
2. David W. Wright and Stephen J. Perkins, J. Appl. Cryst. (2015). 48, 953–961
3. Daniel T. Bowron and Karen J. Edler, Langmuir 2017, 33, 262−271
4. Alan K. Soper, Karen J. Edler, Biochim. Biophys. Acta 2017, 1861, 1652