I wrote my own toy gravity simulation. 2 stars that come very close together at a clock tick will experience a massive force that throws them both right out of the system. This is an artefact of artificially dividing time into clock ticks to make the calculation tractable. As I understand it, 'softening length' is a fudge to stop that happening.
You'd have to use a more sophisticated algorithm with variable time steps for closely interacting particles, I think. And then some way to deal with particles that become bound.
yup. molecular dynamics simulations are hard-core. and the parallelization is highly non-trivial so you need fast fabrics and complex message passing to scale. one of the raisons d'être for supercomputers
