Hi again,<br><br>Mateo is right, the occupations for Co are 0.4 instead of 1. <br>A last question that is a bit different... <br><br>The gap of pure ZnO (no Co impurities) can not be fixed by pure lda+u<br>because the Zn-d states are fully occupied. However, (I guess) the gap must <br>
be sensitive to a hubbard U for oxygen p-states and could be fixed by fitting U_oxygen.<br>However, I am not aware of anyone using Hubbard U for p states... and a quick search <br>in bibliography didnt find anything. <br>
<br>On the other hand Oxygen is in elements list in tabd.f90. That makes me suspect that 1) It might not<br>be completely non sense 2) there might be other attempts to do that. Any comment?<br><br>Nektarios<br><br><div class="gmail_quote">
On Mon, Jun 30, 2008 at 8:53 PM, Matteo Cococcioni <<a href="mailto:matteo@umn.edu">matteo@umn.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;">
<div class="Ih2E3d"><br>
Dear Nektarios,<br>
<br>
I was going to write but Nicola has been faster than me. Nicola is right: probably the reason why<br>
"ortho-atomic" and "norm-atomic" produce similar results is that the atomic wavefunctions in the Co PP<br>
are not normalized. Try to check the occupations in the "atomic" case. are they much bigger than 1?<br>
<br>
Ortho-atomic: atomic wfcs are orthogonalized with those belonging to different atoms.<br></div>
atomic: wfcs are orthogonal only to those belonging to the same atom (there are overlap regions in between atoms)<div class="Ih2E3d"><br>
norm-atomic: quick and dirty fix added to use PPs whose wfcs are not normalized. when these wfcs are normalized it gives the same results as<br>
"atomic".<br>
<br>
In general I would suggest to not look at the value of U itself but rather to the results it produces. I just found a paper: PRL 100, 256401 (2008)<br></div>
where they use U=2 for Co and 5eV for Zn (with Vasp). Why don't you actually try to compute it (PRB 71, 35105 (2005))?<br>
<br>
hope this helps.<br>
<br>
Matteo<br>
<br>
<br>
Nektarios Lathiotakis wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="Wj3C7c">
Hi again,<br>
<br>
As I wrote previously I have a Co impurity atom in ZnO and<br>
trying to find the right Hubbard-U for Co by fitting to experimental Co-d<br>
projected band from J. Appl. Phys. 103 07D130 (2008). A typical input file is in my<br>
previous e-mail.<br>
<br>
I played with U_projection_type parameter and:<br>
<br>
1) 'ortho-atomic' and 'norm-atomic' agree and give the same optimal U for Co<br>
that is around 4eV. Very reasonable value and no referee would ever object.<br>
<br>
2) 'atomic' (the default) gives as optimal U 0.5eV which is much smaller.<br>
<br>
In other words the Co-d projected band you get with U_projection_type='ortho-atomic'<br>
and U_Co = 4 eV is the very close to the band you get with U_projection_type='atomic'<br>
and U_Co = 0.5 eV.<br>
<br>
Why is that difference? The problem with changing the U_projection_type is that only<br>
atomic supports forces.<br>
<br>
Thanks in advance and also to Nicola for his previous reply.<br>
Nektarios<br>
<br>
<br>
<br>
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