What is the energy difference between the octahedral and tetrahedral sites? Are you sure there's no energy barrier at all to the migration? Remember that a "geometry optimisation" is a local energy minimisation method, so it will only tell you the configuration of the nearest (meta)stable state, not necessarily the global energy minimum.

It might also help if you describe the problem in a bit more detail. Is there a specific publication you're trying to reproduce? What calculations are you doing (perhaps even post your input files)?

All the best,

Phil Hasnip

(CASTEP developer)

Hello Sir,

Thanks for the reply, actually I am trying to apply results of "Probing the Li Insertion Mechanism of ZnFe2O4 in Li-Ion Batteries: A Combined X‑Ray Diffraction, Extended X‑Ray Absorption Fine

Structure, and Density Functional Theory Study" by Zhang et al. to my own project on spinel.

There they found 25% ,50% and 75% spontaneous Zn (2+) ion migration from 8a to 16 sites upon 0.5,1.0 and 2.0 units of lithium insertion due to strong elctrostatic repulsion of Zn and Li by Geometrically optimization.

Whereas when I did Geometrical optimization on 1 unit Lithium insertion on my spinel, I found Zinc(2+) ions to be moving very slightly, no where near octahedral positions but in many literature like the one I mentioned there is even experimental proof of Zn migration. In my case space group is I41/amd, tetrahedral site is 4a and vacant octahedral being 8c.

See the attached CASTEP file of Geometrical Optimization as well as the structure of my spinel in cif format.Please reply asap!

Thank You!

Bhrigumoni Deka

You must run al least a NEB calculation or TS

from geometry optimization only you cannot get good results for migration, even for cation (large sized) as in your study.