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Crystal Structure
Crystal Object interface
Crystal Menus
Powder Pattern
Powder Menus Radiation
Here you can describe the radiation corresponding to your experiment (neutron, X-Ray, tube,...). The wavelength is in Angstroem as usual. Set the polarization rate between 0.95 and 1 for synchrotron experiments, and 0 for an X-Ray tube (actually if you use a monochromator it should be above 0, but a precise value is not critical for a global optimization).

2theta correction parameters
These parameters allow to correct for experimental errors in the 2theta positions of reflections, due to a wrong zero, or a misplacement of the sample holder or its transparency. Practically, using the 2theta zero is sufficient (note that it does not necessary correspond to the convention used by other programs, you may have to change the sign and/or to multiply by 2 the value). After each change, you can right-click on the powder pattern graph to update it.

Maximum sin(theta)/lambda
Use this field to limit the extent of the calculations on the powder pattern. It is usually a very good idea to do that, since for a global optimization, high-angle data is useless. A good value is 0.25 Angstroem-1 (corresponding to a resolution of 2 Angstroems), although you can go higher to 0.4 A-1 if you feel there are not enough reflections...

Powder Pattern Background
So far the background can only modelized using linear interpolation between at user-chosen 2theta values. To input the (2theta, intensity) points you must create a text file with a list of "2theta intensity" on each line (2theta in degrees), and load it using the menu. See the tutorials for examples.

If you want to change the points, just change the values in the text file, and reload it from the menu.

There is currently no limit to the number of points, but even for complex backgrounds 10 should be enough.

PowderPatternDiffraction
This allows to describe the contribution of a crystalline phase to the powder pattern.
It is possible to save the calculated structure factors using the menu (note that structure factors above the chosen sin(theta)/lambda limit are not calculated).

Profile parameters
These are the usual profile parameters: Crystal choice
You are asked to choose a crystal structure upon creation of the PowderPatternDiffraction object. You can change it afterwards by clicking on the crystal name.
Global Biso
This can be used as a global temperature factor for this crystalline phase (affects all atoms). This is refinable, although it slows the optimization without helping a lot.
Texture (Preferred Orientation) using the March-Dollase Model
FOX supports optimization of Preferred orientation, usign the March-Dollase model. To add one phase, use the "Phases" local menu. You can then enter the fraction, March coefficient (>1 for needles, <1 for plate-like crystallites), and HKL coordinates for the preferred orientation.

Note: it is very important to use this only as a last resort, or if you know for sure that you have preferred orientation. Taking one more day to prepare carefully a non-textured sample is definitely worth it, since even if a solution is found, it will be much slower - preferred orientation reduces the information available in some direction of the crystal.

If you finally decide to search for preferred orientation parameters, it is recommended to input as much information as possible. For example, you should be able to know what kind of preferred orientation to expect (plates or needles), so that you can restrict the March coefficient to be either >1 or <1 (e.g. use limits [.1;1] or [1;10] - never go below .1 or above 10, that would just slow things). If you know what the preferred orientation vector is, that's even better.

Note that it is possible to use several preferred orientations, but I strongly discourage to do this for a global optimization.

Single Crystal Diffraction Data
DiffractioDataSinglCrystal object interface
Menus
You can use the menus to load data from a text file (either four columns H K L Iobs, or five columns H K L Iobs sigma). If you do not have data, you can also use the "simulation mode" and generate a full list of H K L up to a given 2theta value.
Finally, you can export the structure factors in a text file.

Twinning option
This is a "hack" to have a very basic handling of twinned single crystal data. If selected, comparison between observed and calculated intensities will not be made on individual reflections, but on the sum of intensities of reflections with approximately identical 2theta angle (i.e. not only equivalent reflections).
This allows to search for a crystal structure without any knowledge on the type of twinning, effectively handling the data as "powder data", but without any computing penalty.

Radiation
Same as for powder pattern...
Crystal
You can click on the crystal name to change the crystal structure associated to this data.
Maximum sin(theta)/lambda
Same as for powder pattern...

Global Optimization Algorithms