Maxim, perhaps, you are interesting in calculation of the formation energies.<br>And therefore, I am personally not sure, how is then better (and correct) to estimate this value when Fe atoms have different RMT's in one supercell.<br>
As Laurence very well explained, when "you use different RMTs for the Fe in effect you make them different". <br><br><div class="gmail_quote">2011/4/21 Laurence Marks <span dir="ltr"><<a href="mailto:L-marks@northwestern.edu">L-marks@northwestern.edu</a>></span><br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">An approximate explanation, but first a caveat: dealing with small<br>
RMT's in Wien2k is not completely trivial.<br>
<br>
In Wien2k you have two different basis sets, a radial grid + orbitals<br>
inside the RMT, plane waves outside. If you use different RMTs for the<br>
Fe in effect you make them different. For instance, try setting up a<br>
Fe cell with two different RMTs (i.e. a supercell), converge it then<br>
do aim. You will find that there has been a small charge transfer<br>
between the Fe's, which will go to zero as you increase RKMAX.<br>
<br>
For your problem, I would go beyond setrmt (which is OK, but not<br>
always optimal) and use a smaller RMT for the C (maybe 1.3) and<br>
increase that for the Fe. You will have to do this by hand. Be careful<br>
about going too small with the C as if you do you will lose core<br>
charge (although .lcore helps); you also need to be careful about<br>
losing core electrons from the Fe. In both cases look in case.outputm<br>
to see how far the core integrals are from integers. Scale RKMAX so<br>
RKMAX/min(RMT) is roughly the same (e.g. 3.5), although you need to<br>
add a bit when you decrease the RMTs. Probably something like 5-6<br>
should be good for your problem.<br>
<br>
How to chose the "right" RMTs? I don't have any great wisdom, others<br>
might have. I tend to use RMTCheck (look in the mailing list, or I can<br>
ask Peter to add it to the contributed software) and check that the<br>
step in the gradients at the RMT for the different atoms are<br>
comparable. In most cases this gives results similar to setrmt. In<br>
principle you can also do calculations for different values with<br>
RKMAX/min(RMT) fixed and look for the minimum energy -- the few times<br>
I've done this the results are about the same. Another method would be<br>
to try and balance the charge lost in the core integrals, which gives<br>
a similar result.<br>
<br>
2011/4/21 Maxim Rakitin <<a href="mailto:rms85@physics.susu.ac.ru">rms85@physics.susu.ac.ru</a>>:<br>
<div><div></div><div class="h5">> Thank you Evgenia,<br>
><br>
> I've already seen that link, but I'd like to get information why it is not<br>
> possible from physical point of view.<br>
><br>
> Maxim<br>
><br>
> 21.04.2011 16:53, å×ÇÅÎÉÑ ëÁÂÌÉÍÁÎ ÐÉÛÅÔ:<br>
><br>
> Dear Maxim,<br>
><br>
> identical elements should have identical RMT's.<br>
> This link might help you <a href="http://www.wien2k.at/reg_user/faq/rmt.html" target="_blank">http://www.wien2k.at/reg_user/faq/rmt.html</a> .<br>
><br>
> 2011/4/21 Maxim Rakitin <<a href="mailto:rms85@physics.susu.ac.ru">rms85@physics.susu.ac.ru</a>><br>
>><br>
>> Dear WIEN2k community,<br>
>><br>
>> Is it correct to perform calculations with different Rmt radii for atoms<br>
>> of one type, e.g. Fe?<br>
>><br>
>> I need to calculate total energy of a systems containing one interstitial<br>
>> carbon atom in bcc iron matrix. Carbon has quite large MT-radius comparing<br>
>> with H atom, so StructGen sets Rmt(Fe) to 1.59 a.u. and Rmt(C) to 1.41 a.u.<br>
>> for lattice constant 5.394 a.u. In some papers (C. Domain et al., PRB 69,<br>
>> 144112 (2004)) Rmt(C) is even large than I got (~1.6 a.u.) and Rmt(Fe) is<br>
>> also much larger (~2.4 a.u.). But if I use the radii from the article,<br>
>> WIEN2k doesn't allow me to perform further procedures - nn gives me<br>
>> information about overlapping spheres.<br>
>><br>
>> Can I use Rmt(Fe)=2.4 a.u. in all volume of my supercell except of the<br>
>> nearest iron atoms?<br>
>><br>
>> Thanks in advance for your answers.<br>
>><br>
>> --<br>
>> Best regards,<br>
>> š Maxim Rakitin<br>
>> š South Ural State University<br>
>> š Chelyabinsk, Russia<br>
>> š email: <a href="mailto:rms85@physics.susu.ac.ru">rms85@physics.susu.ac.ru</a><br>
>> š web: <a href="http://www.susu.ac.ru" target="_blank">http://www.susu.ac.ru</a><br>
>><br>
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><br>
><br>
><br>
> --<br>
> Evgeniya Kabliman.<br>
> Insitute of Materials Chemistryš š š šš Vienna University of Technology<br>
> Getreidemarkt 9/165-TC, A-1060 Vienna, Austria<br>
> Tel: +43 1 58801 15674š š š š Fax: +43 1 58801 15698<br>
> <a href="mailto:evgeniya@theochem.tuwien.ac.at">evgeniya@theochem.tuwien.ac.at</a>š š š š š š <a href="http://www.imc.tuwien.ac.at" target="_blank">http://www.imc.tuwien.ac.at</a><br>
><br>
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><br>
><br>
<br>
<br>
<br>
--<br>
</div></div>Laurence Marks<br>
Department of Materials Science and Engineering<br>
MSE Rm 2036 Cook Hall<br>
2220 N Campus Drive<br>
Northwestern University<br>
Evanston, IL 60208, USA<br>
Tel: (847) 491-3996 Fax: (847) 491-7820<br>
email: L-marks at northwestern dot edu<br>
Web: <a href="http://www.numis.northwestern.edu" target="_blank">www.numis.northwestern.edu</a><br>
Chair, Commission on Electron Crystallography of IUCR<br>
<a href="http://www.numis.northwestern.edu/" target="_blank">www.numis.northwestern.edu/</a><br>
Research is to see what everybody else has seen, and to think what<br>
nobody else has thought<br>
Albert Szent-Gyorgi<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Evgeniya Kabliman.<br>Insitute of Materials Chemistryš š š šš Vienna University of Technology<br>Getreidemarkt 9/165-TC, A-1060 Vienna, Austria<br>Tel: +43 1 58801 15674š š š š Fax: +43 1 58801 15698<br>
<a href="mailto:evgeniya@theochem.tuwien.ac.at" target="_blank">evgeniya@theochem.tuwien.ac.at</a>š š š š š š <a href="http://www.imc.tuwien.ac.at" target="_blank">http://www.imc.tuwien.ac.at</a><br>