Re: PDFGUI problem: PDF calculation from a structure, and a test refinement with data registered for the same structure

[Pavol Juhas]

Hi Marcin,

This might happen for zero displacement factor or overly large 

near-peak sharpening factors delta1, delta2.  PDF peaks are not

evaluated if their simulated width is zero.

Hope this helps,

Pavol

On Fri, May 24, 2013 at 2:36 PM, <osza...@gmail.com> wrote:

Hello!

I am having some problems using PDFGUI with a test structure that I have. Whenever I try calculating the PDF all the distances below ca. 3 Angstroms are ignored in the calculation. Instead I get a straight line (with some ripples when low Qmax is used) that goes to 0. Can you please help me find a setting like this minimal distance value for the calculation? It doesn't seem to be the range since it is set from 0.9 to 30A and either 0.9 gets ignored and is substituted by a value close to 3 or there is a parameter I can't find.

This effect is also the cause of high Rw value when I try to fit some measured data against this structure model. I can clearly see in the data the maxima that correspond to the shorter distances (data seems to show approximately the right distances) in the structure but as with PDF calculation the low R region is ignored.

I would greatly appreciate any help and potential solutions to this problem.

Marcin Oszajca

--
You received this message because you are subscribed to the Google Groups "diffpy-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to diffpy-users...@googlegroups.com.
To post to this group, send email to diffpy...@googlegroups.com.
Visit this group at http://groups.google.com/group/diffpy-users?hl=en.
For more options, visit https://groups.google.com/groups/opt_out.
 
 

--

    Dr. Pavol Juhas

    Condensed Matter Physics and Materials Science Department

    Brookhaven National Laboratory

    P.O. Box 5000

    Upton, NY  11973-5000

    tel: +1-631-344-3594

    fax: +1-631-344-2739

[Marcin Oszajca]

Thank you very much Pavol. Without this comment I'm sure I wouldn't handle my problem. I had some very close peaks in the begining of the PDF which by partially overlapping gave rise to a wide peak followed almost instantly by two very sharp ones. Due to this I indeed tried using delta parameters and since I didn't really know what should be the value I wasn't very alarmed with them rising from default. As you suspected this caused the peaks to becom to narrow to interpret. What helped was the use of the sratio parameter accompanied by a reasonable rcut.

Thanks again for your help and I hope somebody may benefit from this if faced with similar problems.

Marcin

2013/5/24 Pavol Juhas <pavol...@gmail.com>