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Dear WIEN2k users and developers,<br>
<br>
I have a couple of doubts about charged supercells. <br>
<br>
1 For the case of charged isolated charged impurities, my question is if
the next sequence of steps is correct:<br>
1.1 Construct the supercell with all the neutral atoms and run (manually,
not with w2web) instgen.<br>
1.2 Edit the case.inst file and I add/remove electrons in the electronic
shell structure of the impurity atom.<br>
1.3 Then, I go on with the whole initialization process by typing
init_lapw. Up to now, lstart always complains, issuing a message
like<br>
NUMBER OF ELECTRONS NE
IZ
7.00000000000
8<br>
but, up to now, this has never been a problem: I just ignore this message
and go through all the initialization process.<br>
1.4 Check that the proper number of electrons appear in case.in2c. Also,
I change the parameter bgch in case.inm (for example, if I removed 1
electron from an oxygen atom, then I type a -1 in case.inm). By the way,
is there any stringent format for this parameter? I mean, I have exactly
the following in the first line of the case.inm file:<br>
BROYD -1.0 YES <br>
With 1 space between “D” and the “-“ and two spaces between the “0” and
the “Y” ... is that correct?<br>
1.5 Finally, I run the scf.<br>
<br>
According to the few discussions of these procedure that I have found in
the mailing list, I would have no doubt that this is the correct
procedure. However, I found a message from Prof. Blaha dated 7 March 2002
in which he answered a doubt “question on charged systems” by
saying:<br>
“ ... In order to make this properly in WIEN, you should
"specify" the missing <br>
charge in case.inm (Otherwise mixer renormalizes
the interstitial charge).<br>
In addition, I would never again run lstart/dstart (or init_lapw), but
just<br>
edit case.in2, remove the desired number of electrons and then
run_lapw.”<br>
So now I am a bit confused and I should like to know if the above
described process is generally correct or if there can be exceptions.
Should I, or should I not, run lstart/dstart?<br>
<br>
2 My second doubt deals with case of a charged vacancy or an impurity
complex. I have not found information about this in the mailing list. The
point is ... where do I add/remove electrons in the case.inm file in
these cases? Say I study the N vacancy in AlN. With all the neutral atoms
I find the expected additional eigenvalues: a a1 (s-like) state just
above the valence band (occupied by two electrons) and three degenerate
t2 (p-like) states, which are resonances in the conduction band, and are
occupied by just one electron. Now, I should like to remove this last
electron, creating a VN1+, i.e., the vacancy in a 1+ charge state. How do
I do it? Should I remove one electron of, say, one of the four
neighboring Al atoms? The same question raises for impurity clusters: If
I work with, say, a MgO cluster in AlN, and I find that occupied states
appear in the band gap, how do I give the cluster a 1+ charge state? Is
there a rule for deciding from which one of the atoms in the cluster
should I remove 1 electron?<br>
<br>
Of course, any struct or whatsoever file in which you can be interested
is at your disposal: just ask me.<br>
<br>
I thank you in advance for any comments, suggestions or ideas about these
topics: this mailing list is really an invaluable source of
knowledge!!!<br>
<br>
Best regards<br>
<br>
Daniel <br><br>
-------------------------------------------------------<br>
Daniel Fernández Hevia<br>
School of Physics<br>
The University of Sydney<br>
Sydney 2006, Australia<br>
Phone: +61 2 9036 5301<br>
email:
<a href="mailto:danielhf@physics.usyd.edu.au">danielhf@physics.usyd.edu.au</a><br>
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