[QE-users] forcing Sn(iv) or Sn(0) charges in a MASnI3 crystal

[JULIEN, CLAUDE, PIERRE BARBAUD]

Dear users,

 

I am working on a MASnI3 crystal. In this structure, the Sn can usually be
considered as a Sn2+ cation. I ran some calculations on the system, and
performed a Bader charge analysis on an all-electron paw charge density. It
seems to confirm that the tin is in Sn(2) configuration with bader charge
48.3 instead of 50 (this is, by the way, inconsistent with the results of
Lowdin analysis as implemented in projwfc.x, which gives pretty much the
full 4d10 5s2 5p2 orbitals of Sn(0) ).

 

So everything is as expected so far (from the Bader point of view at least).
However, I would like to model a MASnI3 with a "defect" consisting of an
"oxidized or reduced" tin atom given by Sn(iv) or Sn(0) in this material.
Indeed, it was reported in J. Mater. Chem. A, 2018,6, 21389-21395 that some
degradation mechanisms can lead to the presence of such states, and I want
to explore their consequence on the material properties.

 

However, I am not sure how to tackle this. My first idea was that I probably
needed to create a pseudopotential with 2 missing or additional valence
electrons. But on second thought, this method might be valid if we have
missing core electrons, but not for valence. I highly doubt that  it would
give me the expected result once I place it in the crystal lattice, given
that there is really no reason for those additional electrons to gently
"stay on their starting atom", so to speak.

 

So is there a reliable method to study such a system by "forcing" an
oxidization state for an atom in a crystal ? This task seems to be made
difficult by the very subjective definition of an "atomic charge" in the
framework of quantum mechanics and DFT.

 

Thanks in advance

Julien

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20190424/c939c26e/attachment.html>