Tamfang Thank you. So when you say “the particles want to be at distance __”, I guess there's attraction as well as repulsion? Or does it only mean that particles out of that range are ignored in generating the forces?
Tamfang It's easy to imagine the electron repulsion algorithm. From the shapes of the holes I guess each hole represents a charge; but that means some of the charges settled on the crossing circle, which I'd expect them to avoid; the charges are effectively twice as dense there as elsewhere. So: Is my imagination wrong? Is my understanding of the model wrong? Did you pin some of the charges to the crossing? Did you run the program many times and pick one with a good crossing?