Dear Julien, I remember that some time ago as I learned about Quantum ESPRESSO I viewed an old conference contribution (from the Quantum ESPRESSO Tutorial recommendations) about DFT+U from Matteo Cococcioni. There he had an example where the calculation of Li0.5FePO4 led to an charge of 2.5 on the Iron atoms with normal DFT. With DFT+U he ended up with half of the Iron atoms in the oxidation state +2 and the other half of the Iron atoms in the oxidation state +3 which is physically more reasonable than the normal DFT result. I don't know how well this applies to your problem but if you want to check the conference contribution here's the link: http://slideshot.epfl.ch/play/kQtOP4iZGwFA
Hopefully this can help Best regards Dominik M.Sc. Dominik Voigt PhD Student Münster University of Applied Sciences Email: [email protected] > 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 > > _______________________________________________ > Quantum Espresso is supported by MaX (www.max-centre.eu/quantum-espresso) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users _______________________________________________ Quantum Espresso is supported by MaX (www.max-centre.eu/quantum-espresso) users mailing list [email protected] https://lists.quantum-espresso.org/mailman/listinfo/users
