Seminari degli  studenti di dottorato. In this talk we will discuss the use of variational methods for investigating crystallization problems. In such problems the typical functionals considered are associated with pairwise interactions potentials depending on the mutual distances between the particles: among them, short range repulsive/long range attractive potentials are very relevant. The talk is divided in two parts: In the first part of the talk we will adapt the classical crystallization model of Heitmann and Radin in order to predict ordered structures assumed by group of animals; in the second part we will prove that crystallization does not occur for a class of potentials known as Mie potentials.