International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by S. R. Hall and B. McMahon © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. G, ch. 3.3, p. 122
Section 3.3.5.2. Simulated data^{a}NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA |
The data items in these categories are as follows:
It is common to calculate powder-diffraction intensities from a crystallographic model. This is necessary for Rietveld refinements, where the model is fitted to the experimentally observed intensities. It is also used to simulate the diffraction pattern of a material for which the structure is known, perhaps for comparison with a measured diffraction pattern.
A crystallographic model can be described in CIF using data items from the core CIF dictionary, as described in Chapter 3.2 . To record the results of the simulation, the data items _pd_calc_intensity_net or _pd_calc_intensity_total are used. The difference between these two data items depends on the treatment of background. If the pattern is simulated with a fitted background added to it, _pd_calc_intensity_total is used; otherwise _pd_calc_intensity_net is used. The values will typically be placed in a loop with the processed (_pd_proc_*) data items or the observed (_pd_meas_*) data items. If neither observed nor processed data are present (e.g. for a simulation), or if, for some reason, the simulation has been performed with a different range or step size, the appropriate _pd_proc_* data items are used to define the values etc. used for the simulation.