[Wien] A general question on LDA+U

[Thomas Claesson]

Dear Wien users and developers!

Inspired by a previous question I came up with this general question on
LDA+U calculations. When working with an LDA+U case with a large U, say 8
or 9 eV, what is the best approach to reach a converged state? Either you
can start from
(1) a calculation whis has converged without the LDSA+U orbital potential,
then slowly turning up U until the desired value is reached, or
(2) a just initialzed (not converged) case with the starting density as
provide by lstart and the (large) desired U-value applied from the
beginning.

Could these two approaches lead to different converged states? Is it
possible to say which of these two approaches is the most reasonable one?

Thanks for your replies!

Best regards,
Thomas Claesson


---------------------------- Original Message ----------------------------
Subject: Re: [Wien] FeO LDA+U
From:    "Peter Blaha" <pblaha at theochem.tuwien.ac.at>
Date:    Wed, June 28, 2006 11:22
To:      "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
--------------------------------------------------------------------------

Do you have an AF rhombohedral cell with 2 Fe atoms and one Ni ?

The Fe have opposite spin ?

If I remember correctly, there was no problem in going from GGA to LDA+U
and getting an insulator.

However, you can play with the density matrix
and occupy the d-z2 (m=0) orbital. Use  x org -up/dn and runsp -orbc for
some steps, until you release it using runsp -orb





> I am trying to do an LDA+U calculation for FeO in the antiferromagnetic
> configuration (AFM).
> I find that even when I start the calculation with the antiferromagnetic
spin
> configuration and a large
> value of U (up to 9eV, J = 0.89), the system goes back to a metallic
> ferromagnetic state.
> I have tried modifying the density matrices and restarting.In this case,
either
> the same happens or the
> Fe magnetic moments wander around and never converge.
>
> Has anyone converged a gapped AFM state for FeO?
> Or at least has anyone noticed the above problem?
>
> In the literature it is a mentioned a few times  that one needs to fully
occupy
> the A1g orbital (rhombohedral system) and deplete the Eg orbitals in order
> to open a gap.
> Has anyone done this successfully for FeO?
>
> Was it sufficient to start with a particular configuration or was
modification
> of the density matrices necessary?
>
> Any help you can provide is greatly appreciated.
>
> Ashley
>
> PS. I am running WIEN2k_04.11 (Release 1/11/2004)
>
>
>
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> John Ashley Alford II
> Oak Ridge National Laboratory
> PO Box 2008  MS6164
> Oak Ridge, TN  37831-6164
> Phone: (865) 576 - 6269
> FAX:   (865) 241 - 0381
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>


                                      P.Blaha
--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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