[Pw_forum] [LDA+U] elements in occupation matrix are real number?

[Chan-Woo Lee]

Dear QE developers and users,

 

I have a question in understanding occupation matrix from LDA+U output file.

 

1) Definition of occupation matrix, n is:

 

n= \sum{f<psi|phi_i><phi_j><psi>}, where psi is KS eigenstates, phi_i is
atomic orbital of i orbital, f is scaling factor. As i and j from phi_i and
phi_j don't have to be identical, I think it's not guaranteed that elements
in n matrix are always real. However, in the QE output, they are all shown
as real numbers. In new_ns.f90, I can find that n (nr and ns) are defined as
real numbers but I can't find any restrictions other than this. 

 

2) While elements in the matrix are real, some of them are "negative". How
can I understand this? I found one paper about multiconfigurational
character of wave functions
(http://jcp.aip.org/resource/1/jcpsa6/v110/i9/p4199_s1 ) but it's beyond my
scope. 

 

Did I miss something? Any suggestions and advices will truly be appreciated.

 

Sincerely,

 

Chan-Woo

 

 

-------
Chan-Woo Lee, Ph.D.

Postdoctoral Research Associate

 

Department of Chemistry
University of Pennsylvania
231 South 34th Street
Philadelphia, PA 19104-6323 
Phone: 1-215-898-3564 (Office)
Email:  <mailto:leechanw at sas.upenn.edu> leechanw at sas.upenn.edu /
<mailto:cwandtj at gmail.com> cwandtj at gmail.com

 

 

 

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