Solids modeled by ab initio crystal field methods. X. Structure of α-glycine, β-glycine, and γ-glycine using a 15-molecule cluster

The structure of three polymorphic forms of glycine in the crystal phase, α-glycine (P21/n), β-glycine (P21), and γ-glycine (P32), 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.