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Methods, Problems and Solutions

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

Changing a histogram (diffraction data file) in GSAS

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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).]

Via the Rietveld Mailing List

Date: Wed, 11 Sep 2002 12:41:15 -0400
From: Xiangyun Qiu [[email protected]]
Organization: Michigan State University
To: [email protected]
Subject: One problem when replacing a histogram.

Hi Dear all,

I encountered one problem when doing batch GSAS refinements:
  When I replace the old histogram by a new one, even though all peak
profile coefficents remain the same, however, diffractometer constants
are
reset to the value in instrument parameter files.  Actually, I want to
use the
refined DIF constant values instead of original values in instrument
parameter
file.
Is there a way to tell GSAS not to replace the diffractometer constants
when
replacing a histogram?

Thanks,

Xiangyun


Date: Wed, 11 Sep 2002 21:00:09 +0200
To: [email protected]
From: Jonathan WRIGHT [[email protected]]
Subject: Re: One problem when replacing a histogram.

The simplest way is to use an instrument parameter file containing the 
correct values for the instrument.  Having said that, the easiest way (that 
I found) to do batch refinements is to change the contents of the datafile 
and run powpref again. So instead of telling GSAS you are replacing a 
histogram, just change the file which has the name GSAS is looking for. 
(eg: set up with data.dat, the when you want to change dataset rename the 
file data.dat and copy the next file in line to data.dat). This avoids the 
need to run expedt at all, you just run powpref then genles, save off and 
then delete the list file and then change the datafile to start again with 
the next pattern. Most programs which can be started from a command line 
can be fooled in a similar way.

HTH,

Jon


Date: Wed, 11 Sep 2002 15:17:06 -0400
From: "Brian H. Toby" [[email protected]]
Organization: NIST Center for Neutron Research
To: [email protected]
Subject: Re: One problem when replacing a histogram.

>Is there a way to tell GSAS not to replace the diffractometer constants
>when
>replacing a histogram?

In a word -- no.

In addition to Jon's good suggestion -- to overwrite the file with the
data file you are planning to substitute, another option is to put each
refinement in a separate directory and then use the same name for each
data file (provided that you did not specify a directory when you read
in the file originally). One last idea is to edit the .EXP file
manually. The file is specified on a line like this:

HST  1  HFIL  garnet.raw

You can change it and then run powpref.

Brian


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