The behavior of nuclear matter is studied at low densities and temperatures using classical molecular dynamics with three different sets of potentials with different compressibility. Nuclear matter is found to arrange in crystalline structures around the saturation density and in non-homogeneous (i.e. pasta-like) structures at lower densities. Similar results were obtained with a simple Lennard-Jones potential. Finite size effects are analysed and the existence of the non-homogeneous structures is shown to be inherent to the use of periodic boundary conditions and the finitude of the system. For large enough systems the non-homogeneous structures are limited to one sphere, one rod or one slab per simulation cell, which are shown to be minimal surface structures under cubic periodic boundary conditions at the corresponding volume fraction. The relevance of these findings to the simulations of neutron star and supernovae matter is discussed.