[ESPResSo] Coalescing Particles/Droplets

[Lorenzo Isella]

Dear All,
I wonder if Espresso can be used to model the interaction of perfectly
coalescing particles (you may think of them as water droplets).
For doing so, I would need to be able to define particle radia r_1 and
r_2 and say that when two particles collide, then the resulting
particle is again a sphere with radius R=(r_1^3+r_2^3)^{1/3}.
I think I can use several potentials to define a particle radius, but
I cannot think of any way to achieve what I want using Espresso (it
may not be doable).
Given and not granted that there is a way of doing what I described
above, the second step would be the generalization such that the
radius of the resulting particle after a collision is:
R=(r_1^d+r_2^d)^{1/d} for d in [1,3].
Can anyone give me a hint?
Many thanks

Lorenzo