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Dear all,<br>
<br>
I am not sure that the initial question of Dean Keeble was about
"partial occupancy" of a site. <br>
In fact the first mail use an ambiguous terminology "fractional
occupancies". See the text below:<br>
<br>
<pre wrap="">Uploading a .cif file and typing the the co-ordinates by hand yield the
same problem - the fractional occupancies in my material are not
correctly inputted. Examining the .struct file doesn't seem to give any
clues either. Can (and if so, how) do I specify fractional occupancies?</pre>
Such terminology is not very clear, because we should speak about
"fractional coordinates" or "partial occupancies", but "fractional
occupancies" has no real meaning. <br>
<br>
So, what do you really want Dean? If you wanted to know how to handle
with "partial occupancies" the answer of Stefaan is perfect.<br>
If, you wants to deals with "fractional coordinates" the answer is
different, and your question must be understand in another way.<br>
<br>
If all your positions are fully occupies and if you have transformed
your cif file in struct file using cif2struct, you must also check if
the space group setting you have is supported by Wien2k (particularly
for low symmetry systems). If not, you should transform your struct
file in such a way to respect the Wien2k space group setting.<br>
<br>
I hope that this mail will be helpfull. Sorry for such comment if the
initial question was really about "partial occupancies".<br>
<br>
<br>
Regards<br>
<br>
Xavier<br>
<br>
<br>
<br>
<br>
<br>
Stefaan Cottenier a écrit :
<blockquote cite="mid45BE037D.6050606@fys.kuleuven.be" type="cite">
<pre wrap="">Pretty hopeless, I'm afraid. Wien cannot deal with fractional
occupancies, it needs real atoms at every site. A correct solution that
would need way too much calculations is to take a rather large
supercell, and to make all possible configurations of atoms that are
allowed within your constraints. Then average your EFG over all these
possibilities. For sure your supercell will need to be too large and the
number of configurations accordingly immense to be of practical use.
There is a possibility to make the 'virtual crystal approximation' by
giving fractional Z-values as input, but its accuracy is doubtfull (even
more for EFG's). See the mailing list archive.
We have been put for a similar problem some time ago (see PRB 74 (2006)
184108), and found it insoluable for EFG's. For Mossbauer isomer shifts,
we could deal with it, however.
Stefaan
</pre>
<blockquote type="cite">
<pre wrap="">Dear all,
I am a relatively inexperienced user of Wien (as my question is sure to
imply more aptly than I realise).
I'm attempting to find the EFG of various ferroelectric ceramics and I
can't seem to enter the structure correctly.
Uploading a .cif file and typing the the co-ordinates by hand yield the
same problem - the fractional occupancies in my material are not
correctly inputted. Examining the .struct file doesn't seem to give any
clues either. Can (and if so, how) do I specify fractional occupancies?
Thankyou in advance for your swift and benignant reply,
Dean Keeble
Dept. of Physics
Warwick University
UK
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