Hi all,<br><br>the option 'atomic' is the default and maybe that should change? I dont know. It created<br>me a lot of trouble however. I confirm Shu-jun numbers (2.6 occupations)... I get the same.<br>I think we used the same functional and consequently potentials for<br>
Zn, O, Co (PBE functional). <br><br>Shu-jun, did you use the same pseudo for Co in ZnO and SnO2?<br><br>With the 'atomic' option in this case , U_Co=0.5 is enough to push all<br>Co-d states into the valence. The rule I found is that the U_Co with option<br>
'atomic' has the same effect as 8*U with option 'ortho-atomic' on the Co-d projected DOS.<br><br>So the self consistent value of Shu-jun correspond to U=2.5eV with ortho-atomic. Of course this applies to <br>
the position of Co-d occupied bands. Dont know about other properties. I will have to <br>repeat calculations with 'ortho-atomic' or 'norm-atomic' option.<br><br>Thanks for the discussion<br>Nektarios<br><br>
<div class="gmail_quote">On Thu, Jul 3, 2008 at 10:16 AM, Nicola Marzari <<a href="mailto:marzari@mit.edu">marzari@mit.edu</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
<br>
<br>
Dear Shu-jun, All,<br>
<br>
<br>
I get very nervous about using U with non-normalized occupations. Even<br>
if U can have some amount of pseudopotential dependency, using it<br>
with unnormalized projectors really messes up any meaningful discussion<br>
of occupation values and U values.<br>
<br>
And of course referees would go nuts at seeing that a U=0.3eV is<br>
relevant - the reason is that that number doesn't really make sense.<br>
<br>
To me, it's an option ("atomic") that should be removed altogether from<br>
the code - others might have other opinions, but if we leave it as it<br>
stands, we risk creating an enormous amount of headaches down the line.<br>
<br>
nicola<br>
<div class="Ih2E3d"><br>
<br>
<br>
<br>
??? Shu-jun Hu wrote:<br>
> Dear All,<br>
><br>
> I would post my comments on the topic of LDA+U calculation of small U_Co.<br>
><br>
> (1) The self-consistently calculated U_Co is indeed sensitive to the oxidation<br>
> state of Co. In Co-doped ZnO DMS, the value is about 0.31 eV, a very "small"<br>
> number. However, in Co-doped SnO2, we got a "reasonable" value of 3.7 eV.<br>
> U_projection_type is specified as the default (atomic) in both cases during the<br>
> calculation of U_Co.<br>
><br>
> (2) The calculated band structure is much sensitive to the value of U_Co and<br>
> U_Co=0.31 eV does have a significant effect with respect to U=0. U_Co=0.31 eV can<br>
> well fit the experimental results (APL 84 4233 (2004), and also J. Appl. Phys. 103<br>
> 07D130 (2008)), where the occupied Co:3d majority state are deep in the valence<br>
> band rather than in the gap. If U_Co=2 to 5 eV is implemented, Nektarios is right:<br>
> a Co-d projected DOS far deep into the valence (completely non sense).<br>
><br>
> (3) The occupation is larger than 1 but not less than 1 in the "atomic" case. A<br>
> piece of output file is listed in the end.<br>
><br>
> Best wishes.<br>
<br>
<br>
<br>
<br>
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