A benchmark method for global optimization problems in structure determination from powder diffraction data

Quasi-Newton–Raphson minimization and conjugate gradient minimization have been used to solve the crystal structures of famotidine form B and capsaicin from X-ray powder diffraction data and characterize the χ2agreement surfaces. One million quasi-Newton–Raphson minimizations found the famotidine global minimum with a frequency ofca1 in 5000 and the capsaicin global minimum with a frequency ofca1 in 10 000. These results, which are corroborated by conjugate gradient minimization, demonstrate the existence of numerous pathways from some of the highest points on these χ2agreement surfaces to the respective global minima, which are passable using only downhill moves. This important observation has significant ramifications for the development of improved structure determination algorithms.