A general, computationally easy method for minimizing the steric energy of a molecule, polymer, surface, or net within the field of a fixed, or periodically updated, crystal lattice has been devised. The goal has been obtained by coupling molecular mechanics (MM) to Kitaigorodsky's atom-atom pairwise potential (AAPP). The primary outcomes of such MMAAPP computations are the "solid state" conformation of the molecule, its intramolecular steric energy and its interaction energy with the surrounding lattice. These computations are ideally suited for studying relative stabilities of different polymorphs, plastic deformations of a whole crystal lattice, and molecular motions of flexible guest molecules in host crystal lattices. The proposed approach can help in understanding solid-state dynamics, factors controlling reactivity in crystal lattices, and crystals as "supramolecular entities". In addition, the capability of building "hypothetical" crystals with sterically reasonable geometries can be exploited in the process of solving crystal structures from partial diffraction data.