Riza (& other newbies),
I personally recommend starting with the web tutorial on alumina (http://www.ncnr.nist.gov/programs/crystallography/software/expgui/tutorial3/index.html). There is a reason why the GSAS manual starts with a "simple" TOF refinement, but it is not where I would recommend starting.
With regard to error indices (chi**2, Rwp, etc.), there is a long history of e-mails on this subject, so I suggest use of google, etc to answer your latter questions. Chi**2 should be 1.0, if the model accounts for all non-statistical errors. Refinements with CW neutrons often come close, but for reasons that vary from project to project, best-fits may have Chi**2 >> 1. When Chi**2 >> 1, the results can be very good or can be garbage. The only way to tell the difference is to understand the source of the errors and how they affect the fitted model.
Brian
Riza Iskandar wrote:
Dear colleages,
I had downloaded the EXP-GUI software several days ago, and right now I'm trying to understand that software. Using example raw file from GSAS example file, I try to run the Nickel TOF file. Could anyone help me to answer these questions?
1. Does anyone have done this problem? (run the nickel example) what is the minimum chi (convergence) can be achieved?
2. Does it need profile refinement?
3. What is the minimum value of chi for every refinement process? I meant what is the minimum value that we can declare that our refinement process is successful?
4. I also did some refinement using APD (Philips Diffractometer) with the same sample as I did by GSAS, but it shows different refinement result, especially in chi value. I am using Pure Fe powder and X-ray diffraction using Co tube. Can anyone explain to me why it is happen?
Thank you for your advanced
*Riza Iskandar*
*Jl. Cinere Raya No 31*
*Depok, Jawa Barat*
*16514*
*Indonesia*
-- ******************************************************************** Brian H. Toby, Ph.D. Leader, Crystallography Team [EMAIL PROTECTED] NIST Center for Neutron Research, Stop 8562 voice: 301-975-4297 National Institute of Standards & Technology FAX: 301-921-9847 Gaithersburg, MD 20899-8562 http://www.ncnr.nist.gov/xtal ********************************************************************
