[QE-users] Ground state of DFT+U

[Matteo Cococcioni]

Dear Malte,

please see below.

Il giorno lun 24 ago 2020 alle ore 19:34 Malte Sachs <
malte.sachs at chemie.uni-marburg.de> ha scritto:

> Dear DFT+U experts,
>
> I am wondering how to know what is the ground state of a DFT+U
> calculation from an ab initio point of view. As approximated DFT is not
> variational I think I cannot use the total energy as an argument.
>
>
This is an open question. DFT+U is only variational at fixed U.


> In my case I have calculated the electronic structure of NdCo in the
> CsCl structure type using QE-6.6. The f-orbitals splits into three
> representations: au, t2u and t2g. For Nd, I expect that it has a valency
> of three and that the t2g orbitals are fully occupied for one spin.
> However, I find that occupying the three t2g orbitals by 2/3 and the au
> orbital by one electron yields a lower energy than the expected
> occupation. So I wonder if I can trust in this "ground state" that is
> against my intuition or if this is a well known effect of DFT+U.
>
>

I know nothing about your system, but it could be a case similar to the
ground state of FeO which we studied it in PRB 71, 035105 (2005).

Hope this helps.

Matteo



> All hints are welcome, best regards,
>
> Malte
>
> --
> Malte Sachs
> Anorganische Chemie, Fluorchemie
> Philipps-Universität Marburg
> Hans-Meerwein-Straße 4
> 35032 Marburg (Paketpost: 35043 Marburg)
> Tel.: +49 (0)6421 28 - 25 68 0
> http://www.uni-marburg.de/fb15/ag-kraus/
>
>
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-- 
Matteo Cococcioni
Department of Physics
University of Pavia
Via Bassi 6, I-27100 Pavia, Italy
tel +39-0382-987485
e-mail matteo.cococcioni at unipv.it <lucio.andreani at unipv.it>
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