A new program package for profile and structure analysis (TOPAS) has been developed with particular emphasis placed on improving stability and convergence. TOPAS is built around a general non-linear least squares system written specifically to integrate various types single crystal and powder diffraction analyses. This includes the ability to refine on laboratory/synchrotron/neutron powder diffraction and single crystal data simultaneously. All currently employed profile fitting techniques such as single line fitting, whole power pattern fitting, whole powder pattern decomposition (according to Pawley and Lebail) as well as Rietveld refinement are supported and can be combined for analysis of multi phase patterns.

A remarkable feature of TOPAS is the ability to determine structures by simulated annealing together with user defineable penalty functions, rigid bodies and lattice energy minimization techniques including user defineable force fields (Coelho, 2000). Structure solution can be performed using step intensity data as well as integrated intensities obtained from powder and single crystal data.

The capabilities of TOPAS for structure determination will be presented using several selected examples.

Reference:

Coelho, A.A. (2000): Whole-profile structure solution from powder diffraction data using simulated annealing. - J. Appl. Cryst., 33, 899 - 908.