Potentialities of Grid Search Method
V. V. Chernyshev · Acta Crystallographica Section A Foundations of Crystallography · 2000
A grid search method is one of the methods, which are now available to facilitate the crystal structure determination from powder data.The advantages of the methods are the simplicity of the algorithm and the easiness of its realization in a computer code.The method is based on two key procedures: systematic translation and rotation of a known, or approximately known, structural fragment within the asymmetric part of the unit cell and subsequent bond-restrained refinement.The flexible use of bond restraints allows the molecule to suffer considerable conformational alterations during the course of refinement, leading to the correct solution even if significant preferred orientation is present, or partly incorrect initial molecular model was used.Potentialities of grid search method will be discussed on the basis of solutions of previously unknown molecular crystal structures of pharmaceutical compounds and anthracene-derived dyes, successfully solved from X-ray, synchrotron and neutron powder diffraction data.A new problem mentioned by some authors, when we can locate molecules in much bigger cells than we could refine by Rietveld method without constraints, will be discussed as well.s10.m1.o4Direct space method and high-resolution Xray powder diffraction : a modern approach to pharmaceutical crystal structure determination.