| Re: Two questions about PDOS calculation of CoO. ( No.1 )|
- Date: 2021/12/02 20:19
- Name: K.Usami
Regarding question (2), I failed to take into account that the space group is different when I distinguish between two Co by the initial number of electrons and not.
I apologize for the lack of consideration, and as for question (1), if you know anything about it, please let me know.
| Re: Two questions about PDOS calculation of CoO. ( No.2 )|
- Date: 2021/12/02 20:55
- Name: T. Ozaki
Though I didn't consider your issue thoroughly, I wonder that the degeneracy of five d-orbitals can be broken
by not only crystal symmetry, but also the electron correlation in the plus U method.
In case of NiO, the charge state is Ni^(2+) and O^(2-) which means that Ni^(2+) has 8 electrons.
The 5 of 8 lectrons populate in the majority t2g and eg orbitals, and the remaining 3 electron populate
the minory t2g orbitals, where there is no effect causing orbital ordering.
On the other hand, Co^(2+) in CoO has 7 electrons, and the majority t2g and eg orbitals are occupied by
the 5 of 7 electrons. The remaining 2 electrons try to populate the minory t2g orbitals, and they choose
a situation that only the two t2g orbitals are occupied, and the other is empty. This is so called orbital ordering.
As a result, the degeneracy of the minority t2g orbitals is broken, and the broken symmetry affects to the
majority orbitals via a broken symmetry in the potential, which is a famous example about how the plus U method works.
I guess that this is what you observed.
| Re: Two questions about PDOS calculation of CoO. ( No.3 )|
- Date: 2021/12/05 00:21
- Name: K.Usami
- Dear T. Ozaki
Thank you for the reply.
I now understand how localized electron correlation causes the degenerate breakdown.
I think I need to learn more about the Plus-U method.
By the way, according to the theory above, the t2g orbitals should be non-degenerate, but why did the degeneracy recover when <Dos.kgrid> was raised?