In the research some physicochemical characteristics (interatomic potentials, internal and surface energies) for hexagonal and cubic gallium nitride (GaN) nanofilms are obtained by using the quantum-chemical and the thermodynamic approach. It is shown that GaN nanofilm in the cubic structure is energetically more stable than in the hexagonal one because its surface energy is significantly lower. This is due to the smaller amount of low coordinated atoms on the surface of the cubic structure of the nanofilm in comparison with the hexagonal GaN nanofilm.