In many cases, the materials selected for inclusion in the database are natural zeolites, whose structures were refined with single crystal data. However, for many of the Framework Types represented, there are no known natural counterparts. In these instances, typical as-synthesized materials have been selected if a suitable structure refinement could be found.

In cases where this was not possible, the best available refinement of the structure of the calcined material was used. It should be borne in mind that powder patterns generated from such data will show significant differences in the peak intensities (particularly at low angles) from the patterns of the corresponding hydrated or as-synthesized materials.

If no reliable structure refinement could be found, coordinates from a framework geometry optimization (DLS refinement) were used. In cases where significant differences are observed in the diffraction patterns of isotypic materials (i.e. those with the same zeolite Framework Type), several reference materials have been included to illustrate the extent of the differences observed as a result of variations in composition and/or symmetry. Outstanding examples are edingtonite and K-F (EDI), gismondine, amicite, gobbinsite, and Na-P1 (GIS) , and as synthesized vs calcined ZSM-5 (MFI). Patterns of the commercially significant X and Y zeolites are also included to complement the natural faujasite (FAU) data.

Compositions are expressed in terms of the full unit cell content. Two compositions are listed: that provided in the original reference and that calculated from the crystal structure data.

The powder diffraction data include the Miller indices (hkl), 2θ value (for the selected radiation), d-spacing and relative intensity for each reflection in the 2θ range specified. The scattering factors used for the framework T- and O-atoms in the structure factor computations are those selected by the authors of the original work. If none were specified, atomic (neutral) scattering factors are used. No adsorption corrections are applied to the data and anisotropic temperature factors have been converted to isotropic temperature factors B(iso) Ų.

The powder diffraction patterns are calculated for the radiation and 2θ range set by the user with the program FOCUS written by Ralf Grosse-Kunstleve (R.W. Grosse-Kunstleve, L.B. McCusker and Ch. Baerlocher, J. Appl. Cryst. 30, 985-995 (1997)). The polarization factor can be changed to reflect the effect of having a monochromator in the beam or of using highly polarized X-rays (e.g. synchrotron radiation).

The intensity scale can be specified in different ways to accomodate extreme situations or to highlight specific regions of the pattern. The intensity is scaled relative to the height of the peak/reflection selected. This linear intensity may differ slightly from the integrated intensity given in the numerical diffraction data.

The powder diffraction patterns are calculated using a pseudo-Voigt (pV) peak-shape function

By default, the 2θ step size is set to 0.02 ° (i.e. the pattern intensity is calculated for every 0.02 ° in 2θ), the background level to 0.0, the Lorentz contribution to 50 (i.e. a = 0.5), the Full Width at Half Maximum (FWHM) to a constant value of 0.07°, and the 2θ range of a reflection to 10 times its FWHM. All of these values can be changed by the user.

The FWHM can be changed by entering the parameters UVW for the function

Many real samples will give diffraction patterns with lines broader than 0.07° as a result of instrumental broadening, disorder, and/or small crystallite size, whereas synchrotron measurements might exhibit lines as narrow as 0.02°. For comparison purposes, it may also be useful to use the V and W parameters to simulate the 2θ dependence of the FWHM.

For patterns with a high Lorentzian contribution, the peak range factor might need to be increased to avoid truncation of the peak "tails".

Images of the zeolite powder patterns are generated as 8 x 6 inch pictures with three different resolutions: 50 dpi, 80 dpi and 110 dpi. The resulting images correspond to the following screen and file sizes.