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Methods, Problems and Solutions

GSAS (General Structure Analysis System) Rietveld powder diffraction and Single Crystal software

Setting Profile Functions in GSAS and setting Default Profiles

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[The reference to use for GSAS in any resulting publications is: A.C. Larson and R.B. Von Dreele, "General Structure Analysis System (GSAS)", Los Alamos National Laboratory Report LAUR 86-748 (1994).]

(Note: for some available XRD parameter files, the default GSAS profile function is the Finger, Cox & Jephcoat peak shape function (#3) which does not have any values for S/L & H/L which can cause the present version of GSAS to crash when running GENLES.

To change the profile function, select, L (Least squares refinement set up) ; O (Edit overall parameters) ; P for (Profile Coefficients) ; then R ("R n - Reset profile coeffs. to default values for type "n"") to change the Profile function type to what you wish to use.

When prompted for the profile type, enter the number corresponding to the profile type. The available profiles will depend on the data type. Refer to page 125 to 138 of the GSAS manual (manual.pdf).

After entering the profile function, if GSAS says no values found, continue on with Y and have them replaced. On being prompted with Enter new values for GU, GV and GW, enter 0 0 0.05. Then when prompted for values for the other parameters, enter / to accept them.

Comments from Bob von Dreele on the above
Date: Tue, 07 Sep 1999 14:01:46 -0600
To: Lachlan Cranswick [[email protected]]
From: [email protected] (Bob Von Dreele)

4. The default profile function is determined by the contents of the iparm
file. The first set of profile coefficients for a "bank" is the default.
Others can also be given as well. I've attached inst_xry.prm from
\gsas\example to show how this is done.
Bob

            123456789012345678901234567890123456789012345678901234567890        
INS   BANK      1                                                               
INS   DTYPE   STND                                                              
INS   HTYPE   PXCR                                                              
INS  1 IRAD     3                                                               
INS  1 ICONS  1.540500  1.544300       0.0         0       0.5    0       0.5   
INS  1I HEAD  DUMMY INCIDENT SPECTRUM FOR X-RAY DIFFRACTOMETER                  
INS  1I ITYP    0    0.0000  180.0000         1                                 
INS  1PRCF1     2    6      0.01                                                
INS  1PRCF11   2.000000E+00  -2.000000E+00   5.000000E+00   0.000000E+00        
INS  1PRCF12   0.000000E+00   0.000000E+00                                      
INS  1PRCF1     3    8      0.01                                                
INS  1PRCF11   2.000000E+00  -2.000000E+00   5.000000E+00   0.000000E+00        
INS  1PRCF12   0.000000E+00   0.000000E+00   0.100000E-01   0.150000E-01        
INS  1PRCF1     4   12      0.01                                                
INS  1PRCF11   2.000000E+00  -2.000000E+00   5.000000E+00   0.000000E+00        
INS  1PRCF12   0.000000E+00   0.000000E+00   0.000000E+00   0.000000E+00        
INS  1PRCF13   0.000000E+00   0.100000E-01   0.150000E-01   0.000000E+00        


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