[QE-users] DFT + U Occupation Matrix Control (OMC)

[Nabeel Anwar]

Dear Louis,

I am interested in the defect chemistry of actinide oxide materials. Currently I am studying the defect formation in  bulk CeO2 using CASTEP and ONETEP. With CASTEP I find without the use of OMC with DFT+U I get what are referred to in the literature as "metastable" states. For example, the removal of an oxygen from bulk CeO2 leaves behind 2 electrons in the vacant site. Each of these electrons should localise onto 1 adjacent Ce site each. Without OMC, the two electrons localise across several adjacent Ce sites, which is a known issue reported in literature.

If you would not mind, I would like to access to QE version with your implementation with OMC.

Affiliation: University of Southampton

Many thanks,
Nabeel

___________________________________________________

Nabeel Anwar MSci, AMRSC

PhD Chemistry

Skylaris Research Group

School of Chemistry, University of Southampton

EPSRC CDT in Theory & Modelling in Chemical Sciences (TMCS)

E-mail<mailto:na5g20 at soton.ac.uk> | LinkedIn<https://www.linkedin.com/in/nabeel-anwar-b0b1b7aa/> | ORCID<https://orcid.org/0000-0003-1221-9256> | ResearchGate<https://www.researchgate.net/profile/Nabeel_Anwar2>


[cid:5d811741-fcb0-4dcc-b730-c166bc502598]

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Ponet Louis Maurice via users <users at lists.quantum-espresso.org>
Sent: Friday, June 10, 2022 16:00
To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: [QE-users] DFT + U Occupation Matrix Control (OMC)

CAUTION: This e-mail originated outside the University of Southampton.

Dear Nabeel,

Currently the only method of having some control over the occupation matrix is by using the flag starting_ns_eigenvalue, together with mixing_fixed_ns. Different from VASP and ABINIT, this only gives you control over the eigenvalues, and the eigenvectors will be those take from the occupation matrix after the first iteration. Depending on what you are trying to do this might be enough. If you need control over the full matrix, I have a personal version where I implemented this, but haven’t gotten around to providing a PR on the official QE code repository. Let me know in case it would be useful to you.

Best,
Louis

—
PostDoc at THEOS, EPFL, Lausanne, Switzerland
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