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<DIV>Thank you, Mateo. You helped me a lot.</DIV>
<DIV> </DIV>
<DIV>Take care</DIV>
<DIV> </DIV>
<DIV>Juanjo</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">Juan J.
Meléndez <BR>Associate Professor<BR>Department of Physics · University of
Extremadura<BR>Avda. de Elvas, s/n 06006 Badajoz (Spain)<BR>Phone: +34 924 28 96
55<BR>Fax: +34 924 28 96 51<BR>Email: melendez@unex.es<BR>Web: <A
href="http://materiales.unex.es/miembros/personal/jj-melendez/Index.html">http://materiales.unex.es/miembros/personal/jj-melendez/Index.html</A></DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=matteo@umn.edu
href="mailto:matteo@umn.edu">Matteo Cococcioni</A> </DIV>
<DIV><B>Sent:</B> Thursday, May 22, 2014 10:59 PM</DIV>
<DIV><B>To:</B> <A title=pw_forum@pwscf.org
href="mailto:pw_forum@pwscf.org">PWSCF Forum</A> </DIV>
<DIV><B>Subject:</B> Re: [Pw_forum] Eigenvectors in a LDA+U
calculation</DIV></DIV></DIV>
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<DIV> </DIV>Dear Juan<BR><BR></DIV>I will try to answer below.<BR>
<DIV>
<DIV>
<DIV class=gmail_extra><BR><BR>
<DIV class=gmail_quote>On Thu, May 22, 2014 at 7:13 PM, Juan J. Meléndez <SPAN
dir=ltr><<A href="mailto:melendez@unex.es"
target=_blank>melendez@unex.es</A>></SPAN> wrote:<BR>
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<DIV>Dear all:</DIV>
<DIV> </DIV>
<DIV>I am playing with the examples for LDA+U. I think that understand that
the eigenvalues and eigenvectors refer to the occupation matrix, which is
calculated from the projections onto the proper states of the atom for which U
correction is to be applied. However, there are two issues which are confusing
to me:</DIV>
<DIV> </DIV>
<DIV>1) If I diagonalize occupation matrix externally to QE, I do get the same
eigenvalues, but quite different eigenvectors, beyond numerical errors, I
think. Could anybody explain to my why does this
happen?</DIV></DIV></DIV></DIV></BLOCKQUOTE>
<DIV><BR><BR></DIV>
<DIV>Maybe you have some degeneracies? If so, any linear combination of
eigenvectors corresponding to the same eigenvalue, is also an eigenvector for
the same eigenvalue. I believe that diagonalization routines always provide
orthonormal eigenvectors but in the eigenspace of degenerate eigenvalues the
phase is arbitrary and can change with the specific routine, machine, compiler,
etc.<BR></DIV>
<DIV><BR><BR> </DIV>
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<DIV>2) Suppose that I need to use the “starting_ns_eigenvalue” option to
correct unreallistic occupations. For that, I have a look at the eigenvalues
of the occupation matrix at convergence. However, since the occupation matrix
changes during the calculation (because the d states, say, may mix together),
the eigenvectors also do. It means that, despite I may know which occupation
is unphysical at convergence, I cannot know what was the corresponding
eigenvalue at the first iteration. Am I right? If so, how can I apply
“starting_ns_eigenvalue” correctly?</DIV></DIV></DIV></DIV></BLOCKQUOTE>
<DIV><BR><BR></DIV>
<DIV>you can try to restart the calculation from the one that produces the
occupation matrix you don't like, having the code reading the potential from it.
It should read also the occupations in this case. However setting
starting_ns_eigenvalue might not be effective in this case because in
electrons.f90 the code is does not allow you to change the occupations if you
are reading them from file. <BR></DIV>
<DIV>Anyway, if you know the eigenvector you want to change the occupation of,
and that eigenvector appears also after the first iteration of the scf cycle,
then you are safe. keep in mind that starting_ns_eigenvalue changes the
occupation matrix eigenvalues only after the first iteration.<BR></DIV>
<DIV> </DIV>
<DIV>regards,<BR></DIV>
<DIV> </DIV>
<DIV>Matteo<BR><BR></DIV>
<DIV> </DIV>
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<DIV> </DIV>
<DIV>Thanks in advance.</DIV>
<DIV> </DIV>
<DIV>Juanjo</DIV>
<DIV> </DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: rgb(0,0,0)">Juan
J. Meléndez <BR>Associate Professor<BR>Department of Physics · University of
Extremadura<BR>Avda. de Elvas, s/n 06006 Badajoz (Spain)<BR>Phone: +34 924 28
96 55<BR>Fax: <A href="tel:%2B34%20924%2028%2096%2051" target=_blank
value="+34924289651">+34 924 28 96 51</A><BR>Email: <A
href="mailto:melendez@unex.es" target=_blank>melendez@unex.es</A><BR>Web: <A
href="http://materiales.unex.es/miembros/personal/jj-melendez/Index.html"
target=_blank>http://materiales.unex.es/miembros/personal/jj-melendez/Index.html</A></DIV></DIV></DIV><BR><BR>
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