[RMCProfile-users] Coordination Constraints question

[Dylan Fast]

Hello,

I have recently been working on some comparative trials for doing RMC work
on a mixed metal oxide (InGaZnO4). I was directed to the old RMCA manual
when looking at coordination constraints which sounds useful since I am
working on a completely amorphous system.

The syntax I am using to add these constraints to the .dat file are as
follows

AVERAGE_COORDINATION_CONSTRAINTS :: 3
 > 2 1 0. 2.4 4.6 0.00001
 > 3 1 0. 2.4 4.6 0.00001
 > 4 1 0. 2.4 5.8 0.00001

General format is
"ATOM 1" "ATOM 2" "Min Dist. for CN" "Max Dist. for CN" "Avg. CN"
"Weighting factor"

I have a few questions regarding the use of these.

1) What is this the correct syntax? I am basing it off of the keyword
listed in the RMC v6 manual and the syntax within the RMCA manual. RMC
recognizes that I want to enforce 3 CN constraints but  I receive an error
"no constraint information given" so I feel that I must be missing a
keyword or have botched the formatting slightly for the lines with the
actual constraint info.

2) I would like to add a coordination constraint for atom #1 (oxygen in
this case) so that is has a total coordination of 2 with any combination of
Ga, Zn, and In. Is this possible or can these constraints only be created
between 2 specific atoms? Is there any way to indicate a set of atoms or
have a wildcard?

3) Can I use non-integer values for the average coordination number? I have
some EXAFS data that suggests the average for the samples I am examining is
around the numbers listed above. It would certainly be possible for me to
use FIXED_COORDINATION_CONSTRAINTS and change it to integer values and then
change the percentages to get the fraction I want but I would like to start
with trying enforcing an average first rather than dictating specific
coordination numbers that are allowed.

4) Should I use MOVEOUT or refine to a null dataset to ensure the system
fits these constraints before doing an actual refinement or is this
unnecessary for this type of constraint?

Please let me know if any of this is unclear and I will be happy to
explain/elaborate.

Best Regards,

Dylan Fast
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