Exercise 4.1: MD for Hard Spheres

Write the MD code for a two dimensional system of hard disks. Set the simple initial configuration with the disk in the vertices of a square lattice. Use a small density and take snapshots. Notice that sometimes, due to the periodic boundary conditions, some particles suddenly appear overlapping another. Limit the time allowed for free flight such that for each particle and each coordinate $\alpha$ the free motion displacement fulfills $\Delta x_{\alpha }\equiv v_{\alpha }\Delta t\leq L/2-d$. To avoid this difficulty one may as well use reflecting boundary conditions, doing a ``billiard dynamics'' simulation.