[ESPResSo-users] is it possible to turn off inertia ?

[Edvin Memet]

Dear all,

Some of the projects I use Espresso for involve low Reynolds 
number/overdamped motion. In such cases, I have to make sure the system 
remains quasistatic, e.g. by allowing it to sufficient time to relax 
after applying a small perturbation. This can pose a problem when the 
relaxation times are long, sometimes resulting in unfeasibly long 
simulation times.

It seems to me that a lot of the computational effort is wasted when 
using the molecular dynamics framework in the case of overdamped motion. 
That is, if you could turn off inertia, you would just have to solve 
force = friction * v and not have to wait for the system to relax (?).

Making mass very small doesn't seem to help, since that introduces 
stability issues - you have to make the time step smaller, and you don't 
really gain anything. The solution (apart from writing your own code), 
as far as I can tell, is to change Espresso's code so it solves the 
force = friction * v equations of motions instead of doing Verlet 
integration (where inertia is implicit).

I'm wondering if people familiar with the code can assess whether this 
is feasible for me to do (does it just entail changing the code at one 
or a few places) or whether it's not worth trying because I would break 
and have to change too many things.

Best,
Edvin