Introduction to physics and thermodynamics
Crystallization and polymorphism - Physico-chemistry of polymorphism

Let's consider a very simple set of spheres in the gravity field. A first layer can be placed on a flat surface, with each sphere in contact with its neighbors. A second layer can then be placed by positioning the spheres as shown in figure 1 a, filling in the voids left between two spheres, thus optimizing the space available.

In this case, the most compact stack possible is obtained, corresponding to minimum potential energy and maximum density. Alternatively, successive layers can be stacked, as shown in figure 1...