Of course! The local moments in an AF insulator can be anything. I just saw that there is only one type of magnetic atom in the unit cell (Ir) and did not think properly. Sorry for that one.

---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 07.08.2017 09:18, schrieb Peter Blaha:
The Ir moments are read from case.scf file, but why should it be near
an integer, and what is the unit of the reported moments in case.scf
file? If the unit is bohr magneton, then for a spin 1/2, should it be ~1.7?

For a FERROmagnetic insulator, the TOTAL spin moment/cell must be
integer. The moments of individual atoms can have any value.

For an ANTIferromagnet, the total spin moment/cell must be zero, and
of course the atomic moments can again have any value.

What you get by :MMT or MMIxxx are spin moments only.

The moments are given in Bohr magnetons (mu_B), but are the spin
moments, not the effective moments. Thus if you have one unpaired
electron the spin moment is one.

PS: For your compound, the orbital moments are probably as important
as the spin moments and you must add them to get the total moment.




The gap can be roughly seen along the k-path I plotted and is checked by
DOS plot, which shows it's an insulator.

Yours sincerely,

Hung-Yu

On Sun, Aug 6, 2017 at 11:03 AM, pieper <pie...@ifp.tuwien.ac.at
<mailto:pie...@ifp.tuwien.ac.at>> wrote:

    A few thoughts on this:

    ad 1)
Presumably Ir is the magnetic ion, so what you describe seems to be
    ok with me. I did not check your .struct file, however.

    ad 2)
    See chapters 4.5.6 and 7.4 of the UG (Wien2k 17.1) on ther
orb-program, and the references therein. Personally I found the .pdf file of his talk on LDA+U very usefull that E. Assmann posted on the
    Wien2k-site.

    Note the recommendation in the UG for the SIC-mode of orb for of
    strongly correlated systems: set J=0 and use only U_eff=U-J. The
    value of U_eff is something you will have to decide, perhaps based
    on the approach described by Madsen and Novak cited in the UG. You
also might want to take a look at eece as an alternative (UG chapter
    4.5.7)

>From many comments here in the mailing list and from the UG (again e.g. chapter 5.5.7, 4.5.8) I take it that PBE is what you should do if you want to calculate spacial charge and spin distributions, but
    to calculate gaps you may have to switch to numerically much more
    costly hybrid methods.

    You probably can (mis)use U_eff as a free parameter to adjust the
    gap in your PBE calculation to your favorite value. However, the
physical meaning of the value would be dubious (imho), and there is
    no guarantee that the Ir-moments simultaneously come near your
favorit 'theoretical moments' (whatever the actual value and origin
    of those is).

    ad 3) Don't bother with the starting values of local moments for
    atomic configurations, and for an antiferromagnet the interstitial
    moment obviously should stay close to zero.

    But the moments you give in your table are very far from integer.
    Are this Ir-spin moments from  case.scf or did you add orbital
    moemnts calculated by lapwdm? The spin moments should be somewhere
    near integer for an insulator.

So, how did you determine the gap in the table? Did you plot a DOS?
    Is this really an insulator, or are there in fact bands crossing
E_F? You might severly misjudge the (direct?) gap depending on where
    in k-space it is and the points in your k-list.

    Good luck

    ---
    Dr. Martin Pieper
    Karl-Franzens University
    Institute of Physics
    Universitätsplatz 5
    A-8010 Graz
    Austria
    Tel.: +43-(0)316-380-8564 <tel:%2B43-%280%29316-380-8564>



    Am 04.08.2017 19:22, schrieb Hung Yu Yang:

        Dear WIEN2k developers and users,

I am trying to do a calculation on Na2IrO3, which has a band gap
        ~340meV and a zigzag antiferromagnetic order in its ground
        state, and
        I have some questions as follow:

        1. To assign the zigzag antiferromagnetic order, what I did is
        that I
first made a cif file that has two inequivalent Ir atoms, and let
        WIEN2k decide the symmetry for me. I adopted the generated
        structural
        file (attached in this mail), checked the cif file in some
        visulization software and made sure they were structurally
        equivalent
except that there were 2 inequivalent Ir atoms instead of 1. Is this the proper way to generate structural files for magnetically ordered
        systems?

2. After generating the desired structural file, I put up on Ir1
        atom
and down on the other (Ir2), used several different combinations
        of U
        and J, and I got the following results:

U(eV) J(eV) Ueff=U-J (eV) Moment(Ir1, Ir2)
          Gap(meV)
        2.1             0.6             1.5
        0.22532,-0.22439        ~700meV
        2.4             0                2.4
        0.30105,-0.30109        ~750meV
        3                0.6             2.4
        0.23225,-0.23235        ~900meV
        3                1.5             1.5
        0.17203,-0.17210        ~900meV

        First, in this test, it seems that the gap is affected by U
        only, not
Ueff=U-J. Second, the moments of Ir seemed to be closely related
        to J.
        In this situation, what is the proper way to assign U and J? I
        am not
sure how much it means if I just try to tune U and J until they
        match
        the experimental gap and/or theoretical moments.

3. I also have a question about the unit of moment given here; I
        understand that the moments depend on the RMT sizes and I
        assumed the
unit is in bohr magneton, but the first value shown for Ir atom is 0.76697 and I am not sure in what unit is this value and how it assigns the initial moment for a certain element (say, Ir in my
        case).
Also, the interstitial moments are nearly 0 among all the cycles.

For this calculation, kpoints=450, RKmax=8 and I had to use the TEMP
        scheme for it to converge. I appreciate any reply from you.

        Yours sincerely,

        Hung-Yu
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