[Pw_forum] projwfc partially occupied levels above Fermi level

[Warren Pickett]

Chris,

If you look at any PDOS for a d atom octahedrally coordinated with oxygen,
you will see e_g DOS mixed in the (filled) oxygen band DOS. e_g orbitals
point at the oxygen and couple strongly with px,py,pz. Most of the e_g
weight is pushed up above the crystal field gap, but a substantial part is
mixed in with oxygen -- this is actually due to antibonding coupling. So it
should be recognized that the weight (and charge) is there, but otherwise
ignore it as a minor complication. And related: don't take "atomic" charges
from DFT codes too seriously. That said, I do look at them a lot.

Warren


Warren E. Pickett
Distinguished Professor of Physics
Department of Physics
University of California Davis
Davis CA 95616, USA
  Cell: 530-220-2138

On Wed, Nov 22, 2017 at 11:00 PM, Christoph Wolf <wolf.christoph at qns.science
> wrote:

> Dear all,
>
> I have a probably silly question I cannot wrap my head around:
>
> a sixfold coordinated FeO6 gives me quite nice, texbtook like
> crystal-field split t2g (dxz, yz, xy) and eg (z^2 x^2-y^2) orbitals after
> running it through projwfc. I am having a hard time interpreting the
> charges, however:
>
> total charge =  14.9828, p =  5.9918, pz=  1.9973, px=  1.9973, py=
> 1.9973,
> total charge =  14.9828, d =  6.7326, dz2=  0.4228, dxz=  1.9623, dyz=
> 1.9623, dx2-y2=  0.4228, dxy=  1.9623,
>
> i.e. the t2g are doubly occupied but the eg have half an electron each
> (~1e in total) which lies above the Ef by ~0.8 eV (i.e. much higher than
> the broadening which was 0.005 Ry); Is this an "residual" electron from the
> ligand field and why is it picket up by the eg orbitals?
>
> Thanks in advance for your help and time!
>
> Best regards,
> Chris
>
> --
> Postdoctoral Researcher
> Center for Quantum Nanoscience, Institute for Basic Science
> Ewha Womans University, Seoul, South Korea
>
>
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