[Pw_forum] How simulate atoms of same element with different oxidation number in compounds?

[Marton]

Hi Máximo,

In my experience, especially when dealing with spinel LiMn2O4, you also
need to address the Jahn-Teller instability induced by Mn3+. If you
slightly distort the spinel unit cell then the two different Mn sites
(formally 3+ and 4+) will naturally emerge during relaxation (of course,
you need the right level of theory as Nicola said): Mn3+ sites will be in a
tetragonally distorted octahedral environment and Mn4+ sites will be in a
more octahedral environment. If you start from a high-symmetry unit cell,
you can also try to break the initial high symmetry of the charge/spin
density by manually distinguishing between the two Mn sites: just name one
type of Mn let's say Mn1 and the other one Mn2 and then use the same
pseudopotential for both. Then, you can initialize the magnetization to a
different value for the two different species.

HTH
Marton Voros

--
Materials Science Division
Argonne National Laboratory

On Mon, Apr 17, 2017 at 8:45 AM, Nicola Marzari <nicola.marzari at epfl.ch>
wrote:

>
>
> Indeed! At the very least, use DFT+U, and/or explore
> hybrid functionals. DFT+U+V seems to be very promising,
> but it's not in the code there.
>
>                                 nicola
>
>
>
> On 17/04/2017 15:36, Ary Junior wrote:
> > Hi,
> >
> > Search for "constrained DFT" and you will find some documents that would
> > be useful for you, like this one
> >
> > http://theossrv1.epfl.ch/Main/OxidationStates
> >
> > Ary Ferreira
> >
> > FAPESP postdoctoral fellow
> > UFSCar - Brazil
> >
> > On Sun, Apr 16, 2017 at 1:06 PM, Máximo Ramírez <aquiles011 at gmail.com
> > <mailto:aquiles011 at gmail.com>> wrote:
> >
> >     Dear,
> >
> >     I'm interested in simulate metal oxide that has two different
> >     valence state (oxidation number) in the same compound.
> >
> >     For example:
> >
> >     Is well-known from experimental results that spinel compounds have
> >     Mn ions with valence +3 and +4, LiMn3+Mn4+O4.
> >
> >     How can I simulate this behavior in QE?
> >
> >     And also, How can I post-process the two atoms like were different?
> >
> >     Thank in Advance!
> >
> >
> >     <https://www.researchgate.net/publication/245108648_Factors_
> affecting_Li_mobility_in_spinel_LiMn_2O_4-A_first-
> principles_study_by_GGA_and_GGA_U_methods>
> >     --
> >     Sincerely,
> >
> >     Máximo Ramírez
> >     Research Assistant
> >     Nanotechnology Laboratory, INTEC
> >     Santo Domingo, Dominican Republic
> >
> >
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> >
> >
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> >
> >
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> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
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