[Pw_forum] GGA+U: Sensitivity of occupation matrix

Chan-Woo Lee cwandtj at gmail.com
Thu Feb 2 23:32:56 CET 2012

Dear QE developers and users:


This is kind of follow-up question of my previous post:


I found that current Ce psp has some critical problems (for both CeO2 and
Ce2O3) and tried to modify the psp. In doing so, I found Ce psp from Prof.
Fabris ( http://www.democritos.it/~fabris/Ce4_ps_f1d1-pbe-rc1.0.uspp.UPF )
and tried it with current O psp. The Ce psp is ultrasoft and the O psp is
RRKJ. Both use PBE functionals. 


In working with the psp, I found interesting results. I tried two cases: 1)
SCF without any atomic relaxation 2) RELAX. I use QE 4.3.2 and Effective U
is chosen as 5.0. Initial structures are adopted from
http://prb.aps.org/abstract/PRB/v75/i4/e045121 . As relax from case 2)
doesn't do much, final structures from two cases are identical. 


While the structures are identical, occupation of f orbitals are different
and DOS are also not the same. For 1) case, occupation is almost 1.0 (~0.9)
at single orbital state which is desirable, I think. Also, DOS shows that
there is no partially filled f states near Fermi level which is the case for
conventional DFT. So, Ce2O3 is predicted to be insulating. For 2) case,
occupations are somewhat even: 0.23, 0.26, 0.29, and 0.12.. Also, electronic
structure doesn't change that much and there is still partially filled f
states. Same atomic structures but totally difference electronic structures.


While I tried to understand and explain this to myself, I can't find any
good answers for this. I am currently testing "starting_ns_eigenvalue" and
"mixing_fixed_ns" to see forcing certain occupations will be helpful or
not.. but I am not sure. 


Any comments or suggestions.???


Chan-Woo Lee, Ph.D.

Postdoctoral Research Associate


Department of Chemistry
University of Pennsylvania
231 South 34th Street
Philadelphia, PA 19104-6323 


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