Later on, this problem was solved by Thompson et al., who derived three virial forms, which are articulated in terms of force contributions to atoms and are independent of interatomic potentials, functioning within the context of PBC. The key idea is to associate each repeating group of atoms with exactly one of the numerous unit cells. As a consequence, the potential energy of the unit cell can be defined as the sum of all potential energy groups associated with the unit cell, represented by