My two cents on the FAQ of Shayam:
Can I conclude FM for my system?
Recall what you may find in your favorite textbook on magnetism about the definitions of para-, dia, non-, ferro-, antiferro-, ferri-, heli-, and whatsoever-magnetic. I think the textbook will say something similar to
DM: When set into an inhomogeneous magnetic field the material experiences a force in the direction of LOWER field. As an alternative it might say that the average magnetic field flux density in the material is smaller than outside. (field is pushed out of a superconductor, frogs can levitate in inhomogeneous magnetic field).
PM: When set into an inhomogeneous magnetic field the material experiences a force in the direction of LARGER field. Alternaatively, the magnetic field flux density in the material is LARGER than outside (magnetic shield materials pull the magnetic field in, clearing some volume outside)
NM: A perfect balance of the two - EVERYWHERE in the material. Exists only in textbooks and in DFT-programs like Wien2k, where equal density of spin-up and -down electrons may be assumed to simplify calculations. The nearest thing nature provides are materials where a diamagnetic response of one part of the electrons cancels a paramagnetic response from another part. That occurs only at a certain temperature and applied field, and only for the overall response, not everyhwere on a local scale.
Note that these three are defined by (linear) response in some applied field - something you usually don't calculate in DFT! This NM-thing is just an abbreviation for 'I wanted to save computing time so I told the program to ignore spin'. This may or may not be a good idea - it depends on what property of which material one is interested in.
The other forms of magnetism may be defined by appearance of a spontaneous magnetization. The spin resolved electronic density breaks the symmetry between up and down spins somewhere, and WITHOUT a field being applied. This is much easier to do in (spin resolved) DFT.
The cases are distinguished by the distribution of the magnetic moments in real space:
FM: All spontaneous moments are parallel. Notice what Lyudmila pointed out: in both, DFT and real materials there will be local diamagnetic response of some electrons coupling to this spontaneous magnetization. The electrons are, after all, NOT independent. Strictly speaking this corresponds to (usually very small) moments pointing in the opposite direction. I am not aware of a rigorous procedure to distinguish small spontaneous moments from induced ones in DFT, but definitely would be interested.
AFM: For each spontaneous moment at point r in the structure pointing in one direction there is one at a symmetry related position with exactly the same size and pointing in the opposite direction.
FerriM: All spontaneous moments are collinear, but not of the same size. This is the most general case standard Wien2k can handle. Notice what Gerhard and Lyudmila pointed out: The structural basis used in the calculation must support the magnetic structure one wants to check. No DFT program will tell you anything about electronic structures not compatible with the symmtry of the structure file.
HeliM: Non-collinear arrangements of spontaneous moments, for example umbrella structures of 4f-moments in rare-earth insulators, or helical spin density waves in metals. The unsupported Wien-NCM might help with such a case.
Notice that the definitions refer to moemnts in real space while the valid quantum numbers of the electronic states are in k-space. There is usually considerable ambiguity in assigning an electron to some atom in the structure. Maybe this works for some 4f-moments with practically all their density within the RMT. For a metal such an assignement obviously can become problematic pretty fast.
To identify FM as the magnetic ground state in DFT you will have to compare calculated total energies of various magnetic structures. If in your case only one U-atom in the crystalografic unit cell of U3O8 carries a sizeable spontaneous moment, then in a calculation based on a single unit cell only PM (no sizeable spontaneous moment in sight) or FM are possible.
Within a single unit cell you might try to find AFM solutions by following Lyudmilas advice: initialize with a sizeable moment in various orientations on all three U-atoms and look what the SCF-cycle does with them. They may all converge to solutions with just one sizeable moment remaining. I gather that this seems to be the case, but I am not sure if you really tried starting from different initial magnetic structures.
As Gerhard pointed out some favorable AFM (or FerriM) structure may be found when sticking with this single magnetic U, but doubling (multiplying) the unit cell and pointing the moment the opposite way in the second unit cell. However, this becomes computationaly expensive pretty fast ...
Good luck, Martin Pieper --- Dr. Martin Pieper Karl-Franzens University Institute of Physics Universitätsplatz 5 A-8010 Graz Austria Tel.: +43-(0)316-380-8564 Am 11.12.2018 23:06, schrieb shaymlal dayananda:
Dear all Sorry, my reply to the original mail chain is waiting for the moderator approval! So I am sending this as a new email. ............................................................ I have actually considered hubard-U (4.5 eV is included) and spin orbital coupling also added. My structure is U3O8, case.indmc -12.0000 Emin cutoff energy 2 number of atoms for which density matrix is calculated 1 1 3 index of 1st atom, number of L, L1 2 1 3 index of 1st atom, number of L, L1 0 0 krad, kls case.inorb 1 2 0 nmod, natorb, ipr PRATT 1.0 BROYD/PRATT, mixing 1 1 3 iatom nlorb, lorb 2 1 3 iatom nlorb, lorb 1 nsic 0..AMF, 1..SIC, 2..HFM 0.3307 0.00 U J (Ry) Note: we recommend to use U_eff = U-J and J=0 0.3307 0.00 U J I am having a followup question for your comments. 1. Can I conclude FM for my system? because: atom-1(uranium1) is non-magnetic, atom-2 uranium (multiplicity is 2 for this atom) has a magnetic moment of 0.71935. These two uranium has parallel magnetism. 2. This system is U3O8, (not U2O5). It has only 11 atoms in the unit cell as 1 (U), 2(U), 2(U), 3(O), 4(O), 4(O), 5 (O), 6(O), 6(O), 7(O), 7(O). With this, is this possible to accept the obtained DOS? (And do we necessarily should get different DOS for FM/AFM cases for their spin UP/DN cases? Thank you Shayam _______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
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