Igor Djerdj schrieb:

The following question is addressed more to FULLPROF users. I want to refine atomic occupancies of Fe-doped TiO2 for instance. Assuming that Ti is substituted with Fe at some sites, how can I provide that the sum of occupancies of Fe and Ti is 1 or 100%?
There are two options I'm aware of:

1) has been mentioned by Alexandre already: Using the same parameter code number for both occupancies, setting the starting values to the correct chemistry and coupling the damping factors to keep the chemistry fixed. This look like this:
Mn1  MN    0.12500  0.12500  0.12500  0.38224   5.00252   0   0   0  0
               0.00     0.00     0.00   261.00   -271.00
Cr1  CR      0.12500  0.12500  0.12500  0.38224   2.99748   0   0   0    0
               0.00     0.00     0.00   261.00    271.00
Mn2 MN 0.50000 0.50000 0.50000 0.38923 2.99748 0 0 0 0 0.00 0.00 0.00 411.00 271.00 Cr2 CR 0.50000 0.50000 0.50000 0.38923 13.00253 0 0 0 0 0.00 0.00 0.00 411.00 -271.00

2) If the distribution is over more than two positions, you can use linear restraints. You can set them in the pcr-Editor. In the .pcr-file it looks like this:
  a) NLI is the number of restraints.
b) The linear restraints themselfs are given behind the distance and angular restraints: Chemcomp 3 28.000000 0.000010 -> Current calculated value: 28.001480
 1.0000  5   2.0000  6   1.0000  7
This example couples the 3 parameters with the code numbers 5, 6, 7 to a total sum of 28. The value of parameter 6 is multiplied by a factor 2 in this summation (to keep a constant charge in a distribution of Na+1 and Ca+2).



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Daniel M. Többens                                Tel.: +43 512 507-5532
Institut für Mineralogie und Petrographie        Fax : +43 512 507-2926
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