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Tutorials and Examples

LHPM-Rietica Rietveld for Win95/NT by Brett Hunter

High Quality Mass Unit-Cell refinement using Le Bail fitting and LHPM-Rietica

The CCP14 Homepage is at http://www.ccp14.ac.uk

[Tutorials page] | [LHPM-Rietica Tutorial Index]

When performing high temperature/high pressure and/or phase transition experiments, it can be important to determine the unit cell results as quickly as possible so this information can be used to plan the next experiment. With Rietveld software using structureless Le Bail fitting, this becomes quite possible even on low quality patterns with impurity peaks due to the whole pattern Le Bail fitting refinement being limited to HKL lines defined by the cell and spacegroup. This can result in a very high quality unit cell refinement with overlapping impurity reflections becoming obvious.

A trick here (that should work with other software such as Fullprof, Powder Cell etc) with LHPM-Rietica is to copy over the optimised HKL file to the next file in the series.

This assumes you have optimised your first (and checked out the middle and end pattern of the series). For information on setting up the first file, refer to Setting up Rietica for doing Le Bail whole profile unit cell refinement

In the following example, initial optimisation found that for this data (Cubic I A 3 D with a=b=c=11.82):

  • Peak profile could be adequately fitted with V W width and the first gamma shape parameter

  • Background was happy with a Shifted Chebyshev I with 3 released parameters.

  • An area of the pattern was excluded (use Right Mouse Button, Insert Excluded) (the blue area in the following screen dumps) that had a nasty impurity peak and overlapped higher up in the sequence with a 0 4 4 peak. It was found other impurity peaks did not cause much of a problem with the refinement.

  • 30 cycles was a good number to perform in this case to ensure convergence.

  • It is useful to have as defaults (via File, Preference:
    • automatic assign data file name,
    • DON'T use a temporary directory,
    • Refine at start and update boxes ticked.


Optimising the first pattern in the series

This has probably been done already but optimise the first dataset in your file sequence by slowing releasing parameters; and get the best fit possible. (don't forget to press the Finish Icon so that the newly refined parameters are updated).

For information on setting up the first file, refer to Setting up Rietica for doing Le Bail whole profile unit cell refinement

Initial optimised pattern


Applying the Previous HKL and Input files to the next dataset of the series

Now using the Windows Explorer (or your favourite file manager) copy over the filename.HKL file and rename it to the next filename in the sequence (i.e., in this case from 0001.HKL to 0002.HKL) where Rietica will use this as your starting intensities.

Now in LHPM-Rietica use File, Save As to save your input file to the new INP file (i.e., in this case from 0001.INP to 0002.INP).

There should be no need to turn off parameters as everything should be stable enough to refine to convergence.


Another quick way of copying Daresbury 16.4 style files is to create a small bat file called c.bat with the following:

copy 000%1.inp 000%2.inp 
copy 000%1.hkl 000%2.hkl
To copy over the files, via a DOS box, type:

c 01 02

(then refine using Rietica on the new set of files)

c 02 03

(then refine using Rietica on the new set of files)

etc, etc


Now refine. (you can use F10 as a speed key). Don't forget to press the Finish Icon so that the newly refined parameters are updated.

Le Bail fitting to get Unit Cell Refinement data


Taking care that the refinement is looking sensible, repeat the above ad-infinitum until you have crunched your data.

Applying HKL and input files from dataset 2 to dataset 3

Le Bail fitting to get Unit Cell Refinement data


Applying HKL and input files from dataset 3 to dataset 4

Le Bail fitting to get Unit Cell Refinement data

Applying HKL and input files from dataset 4 to dataset 5

Le Bail fitting to get Unit Cell Refinement data

Applying HKL and input files from dataset 5 to dataset 6

Le Bail fitting to get Unit Cell Refinement data


[Tutorials page] | [LHPM-Rietica Tutorial Index]

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