Pattern Simulation from d-I Lists
You can simulate powder diffraction patterns from a list of d-spacing and I% values in Jade by
reconstituting peak profiles on the d-I lines, a procedure not to be mistaken for pattern simulation from
crystal structures (see XRD simulation). The quality of simulation is therefore determined primarily by the
accuracy of d-I values. Jade also assumes the I% values of a d-I list to be from integrated peak areas
and will calculate individual peak heights according to the FWHM curve, crystallite size and lattice strain
given in the simulation. You can access this simulation dialog from the 'Analyze | Simulate Pattern...'
menu. An example is shown below:
Jade uses the d-I lists of the PDF overlays in the zoom window to simulate the pattern. If there is more
than one PDF overlay, only the tacked ones will be used in the simulation. Refer to the PDF overlay
toolbar for how to tack PDF overlays. Two types of simulation can be accomplished:
• Create a new diffraction pattern. For a multi-phase mixture, Jade will calculate the overall I% values of
individual phases if their RIR (Reference Intensity Ratio) & wt% values are given; otherwise, Jade will
use their current I% values in the simulation. See the PDF overlay list dialog for how to enter the
desired I%, RIR, and wt% values; an example dialog with 50% rutile, 25% anatase (crystallite
size=250A), 25% hematite is given below:
Jade will clear the current display when you click the Create button on the simulation dialog. The
simulated pattern is not saved to a disk file until you select the 'File | Save | Primary Pattern as...'
menu. You can compare the simulated pattern with the primary pattern if you click the Overlay button
instead of the Create button. You can review the simulated pattern with the zoom & pan tools without
closing the simulation dialog.
• Perform a least-squares fit of simulated profiles to the observed intensities with respect to the I%
values of individual PDF overlays. If the RIRs of all PDF overlays are given, Jade will automatically
compute their wt% values from the fitted I% values using Chung's matrix flushing procedure. The
simulated pattern will be overlaid in the zoom window for comparison. You can find the calculated wt%
values on the PDF overlay list dialog. It should be pointed out that the wt% values thus obtained are
semi-quantitative because profile fitting is not used to obtain the precise areas of individual peaks. With
the Easy-Quant option, you can obtain more accurate wt% values using profile-fitted peak areas. See
the RIR-Quant Analysis topic for more information. With the WPF Refinement option, you can perform
whole pattern fitting and Rietveld structure refinement using structure or structureless phase data to
quantify wt% values as well.
The profile parameters on the simulation dialog are described below:
• The FWHM curve selects the pre-determined instrumental broadening as a function of 2θ angle. See
crystallite size & strain analysis for how to determine your instrument's FWHM curve.
• Besides the FWHM curve, you can broaden the peak profiles further by specifying an overall crystallite
size and/or lattice strain in the simulation. You can also provide crystallite sizes for individual PDF
overlays on the PDF overlay list dialog. This overall crystallite size applies to the PDF phases whose
crystallite sizes are not given. If you click the 'Estimate Sizes' button on the simulation dialog, Jade will
carry out a peak search and estimate the crystallite sizes of individual phases from the FWHM values
of the peaks located near the 100% lines of the phases, and display the results in a phase listing box
on the simulation dialog as shown below:
You can override the estimated sizes by clicking in the 'XS(A)' column and waiting for the input box to
appear. You can hide the phase listing box by clicking the 'Estimate Sizes' button once more. The
lattice strain can be entered as a percentage value (25% max). See crystallite size & strain analysis for
how the strain value is used.
• Skewness of profiles can be specified in the range of -0.9 to +0.9. It applies to both Pearson VII and
pseudo-Voigt profiles.
• You can introduce random noise in the simulated pattern. It is calculated as Noise-Sigmas x
(RND-0.5) x SQRT(I), where RND is a computer-generated random number from 0 to 1, and
Noise-Sigmas is a number you can specify on the simulation dialog.
• You can add background to the simulated pattern only if there is a background curve being displayed
in the zoom window.
• The amorphous area, if added, will be generated using a Lorentzian profile function.
While the current simulation parameters are always remembered by Jade, you can create additional
setting files with the Save button, and restore one of them by selecting it from the setting file list. These
setting files will also appear in the macro task list for automatic pattern processing.