Systems of particles that interact with a force-law will generally aggregate and form clusters that grow depending upon the temperature and range of the interactions. The images below are flow a 2-dimensional system simulation where the particles are effectively "disks" in a flat "box" with perfectly reflecting walls. Particles attract each other over long range distances but repel at very short distances. In the case of the multi-coloured (multi-species) particles, particles of the same colour or species attract, but particles of different species have a weak repulsion. There is therefore a tendency for the colours to aggregate.
(Click on any image to access its full-size conterpart)
These images show phase separation among a population of 4 species of soft disks interacting with a Lennard-Jones form of potential.
In these snapshots a system of 640 single species disk particles slowly aggregate to form crystalline regions.
The particles can be analysed by looking at the "proximity graph" they form - shown above by the lines joining particles that are closer than a certain proximity distance. Or we can look at the sigma parameter of the potential and draw a circle of influence around particles to see which they interact with.