The automatic run
As soon as the input data become available, the following steps are carried out:
Input Data Processing
Checks correctness of input file and completeness of input data. Absorption correction for data collected in trasmission mode (Bragg-Brentano flat sample, Debye-Sherrer capillary sample) can be applied.
Preliminary Procedure
Provides :
a) starting values of scale and profile shape parameters for each phase in the mixture by means of the automatic selection and profile fit of a "single peak" or "reference range".
b) an overall starting value for the 2q zero-shift
c) a background modelling
Rietveld Procedure
Includes:
The whole pattern calculation and an automatic refinement strategy up to convergence: refinable parameters are progressively involved in least squares minimization; numerical restrictions to the parameters and a dynamic variation of the damping factors are applied; the c 2 value is checked cycle-by-cycle in order to control the convergence; parameters getting out of allowed ranges are blocked. As soon as the convergence is reached, the phase weight fractions are calculated. The program stops when
Dxj £ e × s j
for all refined parameters, D xj and s j are the shift and the estimated standard deviation of the parameter j respectively, as obtained by inverting the normal equations matrix, and e = 0.3 (default value).