[Wien] [SPAM?] Should the valence electrons configuration of charge transfer insulators be changed ?

[Peter Blaha]

WIEN2k is an "ab initio" method. You cannot assign a certain number of 
VALENCE electrons to a specific atom. Only core electrons are specific 
to an atom and its occupation can be constraint.

The term "charge transfer insulator" describes a situation if the CBM 
and VBM has states on different atoms, thus an excitation changes the 
"valence" of the atoms. In contrast, a Mott insulator would have CBM and 
VBM on the same atoms (eg. a d-d transition and an excitation does not 
change the charge state.
A charge transfer insulator does not require that you move electrons 
around yourself.

However, often such systems are not well described by standard GGA 
calculations and you may need LDA+U, EECE or hybrid-DFT.
This is also not "ab initio", because you have to make the decision and 
use for metallic fcc Co standard GGA, but for CuO GGA+U, but thats at 
the moment the state of the art.

Am 18.11.2019 um 16:32 schrieb 丁一凡:
> Respected Prof. Blaha,
> 
> Thanks for your detailed explation. The method I followed in the 
> core-EELS calculation is consistent with what you said, setting core 
> hole, adding electrons to background charge, etc. However, if I simply 
> remove one oxygen 2p electron and simply add one electron in Cu 3d orbit 
> to simulate Cu-based HTSC oxides charge transfer insulators, is this 
> method feasible in Wien2k ?
> 
> Best wishes !
> 
> Yifan Ding (Ph.D candidate)
> 
> Institute of Physics, Chinese Academy of Sciences (CAS)
> Address: No.8 Zhongguancun South 3rd Street, Haidian District, Beijing
> 100190 China
> E-mail: yfding0375 at foxmail.com
> 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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