Tables for
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

International Tables for Crystallography (2006). Vol. G, ch. 3.3, p. 122

Section Simulated data

B. H. Tobya*

aNIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA
Correspondence e-mail: Simulated data

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The data items in these categories are as follows:

(a) Part of PD_DATA [Scheme scheme16]

(b) PD_CALC [Scheme scheme17]

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[link] . 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 [2\theta] range or step size, the appropriate _pd_proc_* data items are used to define the [2\theta] values etc. used for the simulation.

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