[GSAS-II] GSAS-II questions

[Bell, Anthony]

Dear all

Thanks to the replies to my emails last week. I am still struggling up the learning curve with GSAS-II.

I have done two of the tutorials with GSAS-II so I am now returning to some of my own data, recently collected for me on I11 at diamond light source. I had done a reasonable refinement using laboratory XRD data here in Sheffield, I am now trying this refinement with synchrotron data to get a better refined crystal structure. My FULLPROF refinement of these data was reasonably good but not great, as I wasn't sure of some of the peak width terms to use for I11. I knew with GSAS I could include an instrument parameter file which would hopefully give me a better starting model for the peak width terms.

Two questions.

Is it possible to refine some peak asymmetry terms in the peak width parameters in GSAS-II?

My synchrotron data is on a synthetic mineral sample with tetrahedrally coordinated silicate framework structure. I wish to put in Si-O bond restraints. I know that there should be 4 Si-O bonds per tetrahedrally coordinates silicon, each bond should be about 1.61 angstroms in length. However, when I add restraints not all of the silicon atoms have 4 Si-O bond restraints calculated, some only have 3 or 2 Si-O bond restraints? Is there some way of manually adding restraints? My previous FULLPROF refinement had 4 Si-O bond length restraints per Si, is it possible to import restraints from a FULLPROF input file?

Thanks in advance

Dr. Tony Bell
Senior X-ray Technician
Materials and Research Engineering Institute
Sheffield Hallam University
City Campus
Howard Street
Sheffield
S1 1WB

Anthony.Bell at shu.ac.uk<mailto:Anthony.Bell at shu.ac.uk>
0114 225 3401

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