The structure of three polymorphic forms of glycine in the crystal phase, alpha-glycine (P2(1)/n), beta-glycine (P2(1)), and gamma-glycine (P3(2)), was completely optimized with standard gradient procedures using a point charge model and using a model constituted of a 15-molecule cluster surrounded by point charges. The calculations were performed with a 6-31G basis set and in the SCF step of the calculations the MIA approach was used. The results for the 15-molecule cluster are in better agreement with the experimental results than the results obtained with the point charge model.