Organisers

• Manuel Athènes (SRMP, CEA/Saclay )
• Florent Calvo (LPQ, Université Toulouse III )
• Anne Boutin (LCP, Université Paris-Sud )

Supports

 CECAM

 SimBioMa

Description

Paths play a central role in molecular simulation, both for
thermodynamic and kinetic studies.
Finding the conditions of phase equilibrium can be achieved by
computing free energy profiles along an adequate integration
path. Similarly, evaluation of rate constants often requires a free energy integration along some reaction coordinate, as in the transition path sampling method.

Direct sampling of configurations has remained essential in
the Metropolis algorithm for many decades. However, sampling of
pathways or entire trajectories instead of configurations
alone has been recently proposed as the basis of more efficient approaches.
Many problems in chemistry or condensed matter physics
(isomerization, folding, structural phase changes...) can indeed be formulated in terms of transformations that take place along pathways, even though the reaction coordinate might not always be easy to identify. In some cases such as polymers, the conformations themselves can be seen as a growing path sampled by dedicated methods.

At the present time, the sampling of pathways has become an important
part of several communities in molecular simulation. Free energies
profiles or differences can be calculated from a single,
quasi-adiabatic trajectory or from an ensemble average over many
non-equilibrium trajectories. Transition path sampling techniques
involve generating sets of trajectories for calculating the rate
constants. Pathways are also a key ingredient of kinetic Monte Carlo algorithms and of the recent waste-recycling scheme.

Scientific Objectives

The aim of the workshop is to bring together scientists from various fields involved with the concept of pathways in molecular simulation.
State-of-the-art algorithms, usually developed and validated on simple
models, as well as applications to more complex systems, will be
presented in order to promote exchanges of techniques and ideas.
Beyond the transposition of standard methods from state ensembles
to path ensembles, the development of new algorithms will be emphasized.


The following computational issues will be addressed:

1. calculation of rate constants for rare events in dynamical
   systems, in or out of equilibrium;



2. calculation of free energy profiles along reaction coordinates;



3. calculation of equilibrium properties from ensemble averages over non-equilibrium trajectories;



4. algorithms involving sampling of paths:
   
   
   
   • kinetic Monte Carlo
   
   
   • rosenbluth bias
   
   
   • waste-recycling
   
   
   • ...
   
   
   
   



5. applications to:
   
   
   
   
   • polymers and biopolymers
   
   
   • materials and nano-structured materials
   
   
   • molecular fluids
   
   
   • ...
   
   
   
   

References

[1]