not a real potential energy surface

difficult to get realistic micelles without apriori information

• easy to underestimate micelle size; 10.1016/j.theochem.2009.09.054
• get N_agg from Guinier analysis; 10.1002/anie.201713303
• run a few simulations at different N_agg pick the best agreement; 10.1002/anie.201713303

let's treat it like an optimisation problem

• move the surfactants to optimise agreement with scattering profile
• micelles are an ensemble structure, perfect for a population approach
• population based optimisation algorithms are trivially parallelised

ctab

single tailed surfactant nearly has C_∞v symmetry

• can describe the system with 5 numbers per molecule
• three positional, two angular

• each particle has knowledge of the personal best (within that member of the population) position and the global best position

• apparently good for high dimensionality problems

shamelessly stolen from wikipedia
By Ephramac - Own work, CC BY-SA 4.0, Link

fitoog

• fitoog is an open-source C_MPI code for applying a particle swarm algorithm fitting SAS data to atomistic/coarse-grained molecular models
• runs a short energy minimisation using MARTINI force field parameters at each stage
• github.com/arm61/fitoog

strong scaling

each node has 20 cores

weak scaling

each node has 20 cores

is it good?

• use fitoog to fit some "test data"
• fifty CTAB molecules in a box
• background subtracted SANS data
• ten independent calcs, running on 16 nodes, population size 10240, number of steps 4000

Random numbers

acceptance probability 0.11 %

Random numbers w/ EM

acceptance probability 0.18 %

Particle swarm w/ EM

acceptance probability 0.26 %

not very micellar