Hello,
I need simulate metal oxide that has two different valence state (oxidation number) in the same compound.
For example:
I'm working with spinel structure, LiMn2O4, experiments have been that the Mn atoms are in Mn3+ and Mn4+ in the compound, like LiMn3+Mn4+O4.
How can I simulate in VASP this behavior?
And also, How can I post-process the two atoms like were differents?
A reference, the link attached.
Thank in Advance!
Article Factors affecting Li mobility in spinel LiMn 2O 4—A first-pr...
Valencies will take care of themselves depending on where the atoms are placed (local coordination, etc.), i.e. atoms will decide what to do depending on their Z and their neighbors etc. This all the point of ab initio calculations, in a sense. Beyond that, it is very hard to pinpoint valency of atoms in extended systems. You may try Bader, Mulliken, muffin tin spheres, SIC occupations, Wannier functions, or play around with DOS's (see attached), but they will all give different results and you'll almost never get a clear cut answer. Generally, very rarely do calculations validate charge ordering (it happens sometimes, see other attachment, but not generally).
I think you can set band occupancy directly and keep it constant. this will probably require bit more effort to setup calculation right. http://cms.mpi.univie.ac.at/vasp/vasp/ISMEAR_SIGMA_FERWE_FERDO_SMEARINGS_tag.html
Thanks for your answers.
But What about if I generate two different pseudopotential for same element but change the atomic configuration.
For example one for Mn with valence 3 and other with valence 4.
If this option valid?
Maximo the best of luck so. with generating PPs. never easy task. but I don't think it is possible, since you have 3d5 4s2. how will you keep 3d 4 electrons core when you want to put 1 electron in valence? you need the whole shell to be either valence or core (I guess).
maximo, generating pseudos with different references (in your case valence) is admissible. but in fact Mn already has all the 3d and 4s in the valence (and sometimes some semicore too). whether it wants to 'donate' how many electrons is entirely up to him and his partners in the system, and you (we) have no say in that.
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