[Pw_forum] Eigenvectors in a LDA+U calculation

[Juan J. Meléndez]

Dear all:

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:

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?

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?

Thanks in advance.

Juanjo

Juan J. Meléndez 
Associate Professor
Department of Physics · University of Extremadura
Avda. de Elvas, s/n 06006 Badajoz (Spain)
Phone: +34 924 28 96 55
Fax: +34 924 28 96 51
Email: melendez at unex.es
Web: http://materiales.unex.es/miembros/personal/jj-melendez/Index.html

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