Dear Malte, please see below.
Il giorno lun 24 ago 2020 alle ore 19:34 Malte Sachs < [email protected]> 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/ > > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users -- Matteo Cococcioni Department of Physics University of Pavia Via Bassi 6, I-27100 Pavia, Italy tel +39-0382-987485 e-mail [email protected] <[email protected]>
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