not a real potential energy surface

difficult to get realistic micelles without apriori information

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
sadie baby 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

sadie baby
each node has 20 cores

weak scaling

sadie baby
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

sadie baby
acceptance probability 0.11 %

Random numbers w/ EM

sadie baby
acceptance probability 0.18 %

Particle swarm w/ EM

sadie baby
acceptance probability 0.26 %
sadie baby
not very micellar
sadie baby

Sadie, my dog