Hi John, Thanks a lot!
On Thu, Jun 15, 2017 at 11:16 PM, Salasin, John <jsala...@vols.utk.edu> wrote: > Wei, > > > > See responses below in Orange. > > > > [image: photo] > > *John Robert Salasin* > PhD Student > > Materials Science and Engineering > > University of Tennessee > > 302-766-0866 | jsala...@vols.utk.edu > > [image: > https://s3.amazonaws.com/images.wisestamp.com/icons_32/linkedin.png] > <http://www.linkedin.com/in/john-robert-salasin-1739bb71> > > > > > > *From:* gsas-ii-boun...@aps.anl.gov [mailto:gsas-ii-boun...@aps.anl.gov] *On > Behalf Of *Wei Liu > *Sent:* Wednesday, June 14, 2017 8:55 PM > *To:* gsas...@aps.anl.gov > *Subject:* [GSAS-II] GSAS 2 inquire > > > > Hi, > > I am a new user of GSAS 2. I am trying to use GSAS 2 by reading the 'Help > for GSAS-II'. However, I have some doubts, which cannot be found in this > web page. Could someone advice on my questions below? Thanks a lot. > > 1. In the 'Unit Cells List', what is the 'Max Nc/Nobs 4 Start Volume 25 > Use M20/(X20+1)?' What is the function of the refinement to this parameter? If > I recall correctly this is used when trying to determine an unknown crystal > structure. The program will fit the peaks locations to all possible crystal > structure and use that function above as a weighting variable to say which > is more likely. > > 2. In the 'Phase Data'/ 'Atoms' tab, for each of the atoms, there are > refinement choices, 'X, XU, U, F, FX, FXU, FU'. May I know what is the > difference between these choices? X will refine atom positions, U will > refine their thermal parameters, F will refine they fractional occupancies. > XU, FX, FXU, FU are just a combination of the above. If you do XU it will > refine the thermals and site positions, and if you do FXU it will refine > the positions, thermals, and occupancies. > > Btw, may I know whether there is a more detailed manual of GSAS 2 besides > the 'Help for GSAS-II'? This has not been developed as the program is > still being developed. A lot of the math is the same from GSAS I and the > manual for it is well documented. Normally you can find the information you > are looking for in that manual. http://www.ccp14.ac.uk/ccp/ > ccp14/ftp-mirror/gsas/public/gsas/manual/GSASManual.pdf > > And if a good reference document or book could be recommended for the > procedure of using GSAS 2 and the theory (including those important > parameters to refine in a normal neutron powder diffraction pattern) for > the refinement of a neutron diffraction pattern, it will be very helpful as > well. I would follow all the tutorials on the GSAS II website and do a > lit review on the Rietveld refinement process as a whole. Research gate > also has some good information. > > Thank you very much for your help in advance, > > Best regards, > > Liu Wei >
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