Whole-profile structure solution from powder diffraction data using simulated annealing

Techniques and methods to facilitate the solution of structures by simulate d annealing have been developed from the starting point of a space group an d lattice parameters. The simulated-annealing control parameters have been systematically investigated and optimum values characterized and determined . Most significant is the inclusion of electrostatic-potential penalty func tions in a non-linear least-squares Rietveld refinement procedure. The long -range electrostatic potentials are calculated using a general real-space s ummation which can be used for all space groups. In addition, a general wei ghting scheme for penalty functions negates the need to determine weighting schemes experimentally. Also investigated and improved is the non-linear l east-squares minimization procedure used in the refinement of structural pa rameters. The behaviour and success of the techniques have been tested on X -ray diffraction powder data against the known structures of AlVO4 in P1 wi th 18 atoms in the asymmetric unit, K2HCr2AsO10 in P3(1) with 15 atoms in t he asymmetric unit excluding hydrogen, and [Co(NH3)(5)CO3]NO3 .H2O in P12(1 ) with 15 atoms in the asymmetric unit excluding hydrogen.