15.2.1 GEOMETRY OPTIMIZATION

In this study the semiempirical method was used for describing the potential en­ergy function of the system. Next a minimization algorithm is chosen to find the potential energy minimum corresponding to the lower-energy structure. Iterations number and convergence level lead optimal structure. The optimizing process of structures used in this work was started using the AM1 method, because it gener­ates a lower-energy structure even when the initial structure is far away from the minimum structure.

The Polak-Ribiere algorithm was used for mapping the energy barriers of the conformational transitions. For each structure, 1350 iterations, a level convergence of 0.001 kcal/mol/A and a line search of 0.1 were carried out.