[ESPResSo-users] Gluing Particles Together

[Lorenzo Isella]

Dear All,
I have a question about the choice of the particle interacting potential 
for my simulations.
Consider a Nx3 matrix

x_1 y_1 z_1
x_2 y_2 z_2
........
x_N y_N z_N

where (x_i,y_i,z_i) are the coordinates of the centre of the i-th 
(spherical) particle within a particle aggregate. Each particle has a 
radius R.
What is essential for me is to make this structure stiff, i.e. each of 
these aggregates should be a rigid body.
In order to achieve this, a radial interaction potential among the 
particles is not enough (particles may slide while preserving their 
relative distances if the potential is purely radial).
In the case of straight linear chains, I solved the problem by using a 
combination of a radial potential to fix the distances between particles 
on top of a 3-body bond angle interaction which acted as a penalty 
function for any chain deformation.
It is not, however, clear to me how to generalize this to aggregates of 
arbitrary shape.
Any suggestion is welcome.
Cheers

Lorenzo