Abstract
Using molecular simulation to aid in the analysis of neutron reflectometry measurements is commonplace. However, reflectometry is a tool to probe large-scale structures, and therefore the use of all-atom simulation may be irrelevant. This work presents the first direct comparison between the reflectometry profiles obtained from different all-atom and coarse-grained molecular dynamics simulations. These are compared with a traditional model layer structure analysis method to determine the minimum simulation resolution required to accurately reproduce experimental data. We find that systematic limits reduce the efficacy of the MARTINI potential model, while the Berger united-atom and Slipids all-atom potential models agree similarly well with the experimental data. The model layer structure gives the best agreement, however, the higher resolution simulation-dependent methods produce an agreement that is comparable. Finally, we use the atomistic simulation to advise on possible improvements that may be offered to the model layer structures, creating a more realistic monolayer model. Usage: Electronic Supplementary Information (ESI) including all analysis/plotting scripts and figure files, allowing for a fully reproducible, and automated, analysis workflow for the work presented is available at https://github.com/arm61/sim_vs_trad (DOI: 10.5281/zenodo.3254719) under a CC BY-SA 4.0 license. Reduced experimental datasets are available at DOI: 10.15125/BATH-00586, under a CC-BY 4.0 license.
Highlights
Neutron and X-ray reflectometry techniques are popular in the study of layered structures, such as polyelectrolyte-surfactant mixtures [1], lipid bilayer systems [2], electrodeposited films [3], and dye-sensitised solar cell materials [4]
The chemically-consistent model was used to determine the structure of the lipid monolayer, Table IV gives the optimum values for the parameters that were varied in the model
This work presents, for the first time, a direct comparison between a traditional method for analysis of neutron reflectometry measurement with analysis derived from a range of all-atom and coarse-grained molecular dynamics simulations; using the all-atom Slipid, the united-atom Berger, and the coarse-grained MARTINI potential models
Summary
Neutron and X-ray reflectometry techniques are popular in the study of layered structures, such as polyelectrolyte-surfactant mixtures [1], lipid bilayer systems [2], electrodeposited films [3], and dye-sensitised solar cell materials [4]. Unlike other surface-sensitive techniques, such as atomic force microscopy (AFM) or scanning electron microscopy (SEM), reflectometry methods can investigate buried interfaces in addition to the material surface. This is due to the ability of neutrons and X-rays to probe more deeply into a material than an AFM tip or the electron. The growth in popularity of reflectometry techniques can be attributed to the significant development of both neutron and X-ray reflectometry instrumentation, such as FIGARO, the horizontal neutron reflectometer at the ILL [6], and the beam deflection system at the I07 beamline of the Diamond Light Source [7].
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