MODELING CRYSTAL-STRUCTURES BY NUMERICAL-METHODS - A TOOL FOR PRACTICAL STRUCTURE-ANALYSIS

Molecular mechanics calculations on crystals have been performed by us ing a simplex optimization and a simulated annealing procedure. Empiri cal Coulomb-Lennard-Jones potentials with an additional set of 10-12 p otentials to describe hydrogen bond interactions were used to model cr ystals (i) with periodic boundary conditions including the interaction s of 27 unit cells and (ii) including 729 unit cells (called extended neighbor model). The restrictions imposed by the respective space grou p were taken into account. As test examples formamide, 1-dimethylethyl )-2-hydroxycyclopentanecarboxamide, ,1-dimethylethyl)-2-hydroxy-cyclop entanecarboxylic acid, and ,1-dimethylethyl)-2-hydroxy-cyclopentanecar boxylic acid were used. Theoretically predicted structures are found t o be in excellent agreement with the experimental structures, if exten ded neighbor interactions are taken into account.