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<div class="moz-cite-prefix">Dear Charlie,</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I join Martin's recommendation to try
LDA+U. By looking at the non-integer total magnetic moment per
unit cell 14.88 muB, I guess you obtained (semi)metallic state,
which might or might not be what you want. Pure GGA sometimes
leads to metallic solution for iron oxides (even for those they
are good insulators). I don't know how pronounced the
semi-metallic character should be for greigite, probably much more
than for magnetite, but even then the value of 14.88 muB looks
quite far from 16.00 muB. (For magnetite you should reach this
integer value even without LDA+U.)</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Anyway, the LDA+U approach will also
help you stabilizing the desired spin structure quite efficiently.
I would be surprised if the moments flipped when you have some U
(a few eV) applied to 3d states of Fe. In fact, you can use LDA+U
just to get close to desired spin structure and then try to remove
it ....<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">And additional note: when reducing the
symmetry of magnetite be aware of the fact that it is a
mixed-valence compound (and I guess greigite might be similar
case) and has a tendency to localize the minority electron within
the octahedral sublattice. When you split the eight octahedral Fe
into four sorts they can readily differentiate to Fe2+ and Fe3+.
(Even in the cubic phase.) Which again may or may not what you
want to have in your model. (With +U you will definitely get the
Fe2+ / Fe3+ scenario, unless you keep all octahedral Fe
equivalent.)<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Regards,</div>
<div class="moz-cite-prefix">Vojtech<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 17-Apr-19 12:00, Penny, Charles
wrote:<br>
</div>
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Dear all,</div>
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<br>
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Thanks for your prompt and helpful replies. </div>
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<br>
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I have run runfsm initially before switching to runsp, but no
luck. It immediately converges back to the ferrimagnetic
solution.</div>
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<br>
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This raises two further thoughts/questions in my mind.</div>
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1) I am assuming that runfsm is NOT an acceptable replacement
for runsp with regards to projecting the total energy onto the
Heisenberg model. In any case I obtain a large moment in the
interstitial region which likely invalidates such a move.</div>
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<br>
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2) I find it interesting that this process works without problem
for Fe3O4, but seems presently rather futile with Fe3S4. Simply
swapping O for S in the lattice (not quite, of course) appears
to create such instability in alternative spin configurations.
Is anyone aware of anything I could look into which might be
able to explain this, or is it just a case of 'bad luck' for
this material and move on if I can't get any improvement?</div>
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<br>
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Re: Magnetite</div>
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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An interesting material without a doubt. Luckily I'm not
investigating the low temperature phase, otherwise I might have
more of a headache!</div>
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font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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Regards,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
Charlie</div>
<hr style="display:inline-block;width:98%" tabindex="-1">
<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt"
face="Calibri, sans-serif" color="#000000"><b>From:</b> Wien
<a class="moz-txt-link-rfc2396E" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at"><wien-bounces@zeus.theochem.tuwien.ac.at></a> on behalf of
Stefaan Cottenier <a class="moz-txt-link-rfc2396E" href="mailto:Stefaan.Cottenier@UGent.be"><Stefaan.Cottenier@UGent.be></a><br>
<b>Sent:</b> 17 April 2019 08:50<br>
<b>To:</b> A Mailing list for WIEN2k users<br>
<b>Subject:</b> Re: [Wien] Magnetic moments converging in a
different direction to the one they are defined</font>
<div> </div>
</div>
<div class="BodyFragment"><font size="2"><span
style="font-size:11pt;">
<div class="PlainText">Dear Martin,<br>
<br>
You trigger long-forgotten memories... ;-)<br>
<br>
Amazing that you remember that talk. That was the only way
in which these results were ever communicated, there was
no paper. The reason for this was that we did observe very
clear and smooth energy dependences upon continuous
rotation of the Fe-moments in different ways and for
different configurations, yet the overall picture was a
messy paradox (= looking at one individual result would
lead to one conclusion, looking at another individual
result would lead to an opposite conclusion).<br>
<br>
There has always been the feeling that once we should
revisit this, but it never got realized so far. Perhaps,
if you feel like...<br>
<br>
Best regards,<br>
Stefaan<br>
<br>
<br>
> -----Original Message-----<br>
> From: Wien
<a class="moz-txt-link-rfc2396E" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at"><wien-bounces@zeus.theochem.tuwien.ac.at></a> On Behalf
Of<br>
> pieper<br>
> Sent: Tuesday, April 16, 2019 12:51 PM<br>
> To: A Mailing list for WIEN2k users
<a class="moz-txt-link-rfc2396E" href="mailto:wien@zeus.theochem.tuwien.ac.at"><wien@zeus.theochem.tuwien.ac.at></a><br>
> Subject: Re: [Wien] Magnetic moments converging in a
different direction to<br>
> the one they are defined<br>
> <br>
> Fe3O4 being an old but unsatisfied love of mine a few
additional<br>
> comments:<br>
> <br>
> Determining exchange constants by spin reversal only
makes sense if the<br>
> changes in electronic structure are small (see e.g.
P. Novak et. al PHYSICAL<br>
> REVIEW B 71, 184433, 2005).<br>
> <br>
> This (usually) works best in insulators, it is a
delicate problem in metals, and<br>
> much more so in Fe3O4 with its Vervey transition.
Here a very intricate<br>
> coupling between electronic and structural degrees of
freedom is at work. I<br>
> seem to recall that the low temperature phase is a
comlicated mess (see e.g.<br>
> Novak et al, PRB 61, 1256, 2000 and references
therein). So complicated that,<br>
> as far as I remember, in the early 2000nds
S.Cottenier, R. Laskowski, J. Rusz,<br>
> M. Rots and P. Novak gave a talk on a Wien2k Workshop
calculating<br>
> exchange interactions in magnetite using the
non-collinear magnetism<br>
> version NCM-Wien2k. Unfortunately I don't have time
to search for<br>
> literature on that one, but you probably don't want
to get into NCM anyway.<br>
> <br>
> However, I don't think you can avoid DFT+U or +EECE -
at least not for Fe3O4.<br>
> I am sure you can find a lot of literature on DFT+U
and +EECE of Fe3O4,<br>
> among others by Novak, Madsen, ... This may
introduce an additional<br>
> parameter in your comparisons of your structures. If
you are using an older<br>
> version of Wien2k, upgrade! Wien26_16 had a bug with<br>
> DFT+U (see<br>
> <a href="https://www.mail-" moz-do-not-send="true">https://www.mail-</a><br>
>
<a class="moz-txt-link-abbreviated" href="mailto:archive.com/wien@zeus.theochem.tuwien.ac.at/msg15590.html">archive.com/wien@zeus.theochem.tuwien.ac.at/msg15590.html</a>).<br>
> <br>
> Best regards,<br>
> <br>
> Martin Pieper<br>
> <br>
> <br>
> ---<br>
> Dr. Martin Pieper<br>
> Karl-Franzens University<br>
> Institute of Physics<br>
> Universitätsplatz 5<br>
> A-8010 Graz<br>
> Austria<br>
> Tel.: +43-(0)316-380-8564<br>
> <br>
> <br>
> Am 2019-04-16 10:29, schrieb Penny, Charles:<br>
> > Dear all,<br>
> ><br>
> > I am running spin-polarised calculations on a
range of iron-spinel<br>
> > structures (namely, magnetite (Fe3O4), maghemite
(gamma-Fe2O3) and<br>
> > greigite (Fe3S4)) with the objective of
calculating magnetic exchange<br>
> > energies in these minerals. This requires
calculating total energies<br>
> > of lot of different spin configurations. This
process has worked well<br>
> > for magnetite and maghemite, but I have
encountered a problem with<br>
> > greigite.<br>
> ><br>
> > When I run a calculation on a spin
configuration of greigite that<br>
> > isn’t the ferrimagnetic ground state (e.g. a
ferromagnetic<br>
> > configuration) the calculation converges to the
ferrimagnetic<br>
> > solution, with the sublattice moments pointing
in opposing directions.<br>
> ><br>
> ><br>
> > In the examples below, I have used a
low-symmetry unit cell with<br>
> > eight unique iron atoms which allows me to
calculate the required<br>
> > number of spin configurations for estimating
J_ij. Atoms 1-4<br>
> > correspond to A site iron atoms in the spinel
structure, atoms 5-8<br>
> > correspond to B site iron atoms and atoms 9-16
are sulphur atoms. In a<br>
> > ferrimagnetic system the A and B sites have
opposing moments and<br>
> > sulphur atoms are non-magneitc.<br>
> ><br>
> > When I define a ferrimagnetic spin
configuration, the calculation<br>
> > proceeds as expected, with the final moments
looking like;<br>
> ><br>
> > rkmax_8_k_500.scf::MMINT: MAGNETIC MOMENT IN
INTERSTITIAL =<br>
> > -0.05116<br>
> ><br>
> > rkmax_8_k_500.scf::MMI001: MAGNETIC MOMENT IN
SPHERE 1 =<br>
> > 2.47349<br>
> ><br>
> > rkmax_8_k_500.scf::MMI002: MAGNETIC MOMENT IN
SPHERE 2 =<br>
> > 2.47348<br>
> ><br>
> > rkmax_8_k_500.scf::MMI003: MAGNETIC MOMENT IN
SPHERE 3 =<br>
> > 2.47348<br>
> ><br>
> > rkmax_8_k_500.scf::MMI004: MAGNETIC MOMENT IN
SPHERE 4 =<br>
> > 2.47348<br>
> ><br>
> > rkmax_8_k_500.scf::MMI005: MAGNETIC MOMENT IN
SPHERE 5 =<br>
> > -3.01699<br>
> ><br>
> > rkmax_8_k_500.scf::MMI006: MAGNETIC MOMENT IN
SPHERE 6 =<br>
> > -3.01699<br>
> ><br>
> > rkmax_8_k_500.scf::MMI007: MAGNETIC MOMENT IN
SPHERE 7 =<br>
> > -3.01699<br>
> ><br>
> > rkmax_8_k_500.scf::MMI008: MAGNETIC MOMENT IN
SPHERE 8 =<br>
> > -3.01699<br>
> ><br>
> > rkmax_8_k_500.scf::MMI009: MAGNETIC MOMENT IN
SPHERE 9 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI010: MAGNETIC MOMENT IN
SPHERE 10 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI011: MAGNETIC MOMENT IN
SPHERE 11 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI012: MAGNETIC MOMENT IN
SPHERE 12 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI013: MAGNETIC MOMENT IN
SPHERE 13 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI014: MAGNETIC MOMENT IN
SPHERE 14 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI015: MAGNETIC MOMENT IN
SPHERE 15 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMI016: MAGNETIC MOMENT IN
SPHERE 16 =<br>
> > -0.03675<br>
> ><br>
> > rkmax_8_k_500.scf::MMTOT: SPIN MAGNETIC MOMENT
IN CELL =<br>
> > -14.88108<br>
> ><br>
> > Final energy;<br>
> ><br>
> > rkmax_8_k_500.scf::ENE : ********** TOTAL
ENERGY IN Ry =<br>
> > -43322.30312592<br>
> ><br>
> > However, when I define a ferromagnetic spin
configuration the system<br>
> > converges to a ferrimagnetic solution with final
moments;<br>
> ><br>
> > k_500_rkmax_8.scf::MMINT: MAGNETIC MOMENT IN
INTERSTITIAL =<br>
> > 0.05118<br>
> ><br>
> > k_500_rkmax_8.scf::MMI001: MAGNETIC MOMENT IN
SPHERE 1 =<br>
> > -2.47348<br>
> ><br>
> > k_500_rkmax_8.scf::MMI002: MAGNETIC MOMENT IN
SPHERE 2 =<br>
> > -2.47347<br>
> ><br>
> > k_500_rkmax_8.scf::MMI003: MAGNETIC MOMENT IN
SPHERE 3 =<br>
> > -2.47346<br>
> ><br>
> > k_500_rkmax_8.scf::MMI004: MAGNETIC MOMENT IN
SPHERE 4 =<br>
> > -2.47346<br>
> ><br>
> > k_500_rkmax_8.scf::MMI005: MAGNETIC MOMENT IN
SPHERE 5 =<br>
> > 3.01697<br>
> ><br>
> > k_500_rkmax_8.scf::MMI006: MAGNETIC MOMENT IN
SPHERE 6 =<br>
> > 3.01697<br>
> ><br>
> > k_500_rkmax_8.scf::MMI007: MAGNETIC MOMENT IN
SPHERE 7 =<br>
> > 3.01697<br>
> ><br>
> > k_500_rkmax_8.scf::MMI008: MAGNETIC MOMENT IN
SPHERE 8 =<br>
> > 3.01697<br>
> ><br>
> > k_500_rkmax_8.scf::MMI009: MAGNETIC MOMENT IN
SPHERE 9 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI010: MAGNETIC MOMENT IN
SPHERE 10 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI011: MAGNETIC MOMENT IN
SPHERE 11 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI012: MAGNETIC MOMENT IN
SPHERE 12 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI013: MAGNETIC MOMENT IN
SPHERE 13 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI014: MAGNETIC MOMENT IN
SPHERE 14 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI015: MAGNETIC MOMENT IN
SPHERE 15 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMI016: MAGNETIC MOMENT IN
SPHERE 16 =<br>
> > 0.03675<br>
> ><br>
> > k_500_rkmax_8.scf::MMTOT: SPIN MAGNETIC MOMENT
IN CELL =<br>
> > 14.88103<br>
> ><br>
> > Final energy is the same as in the
ferrimagnetic case;<br>
> ><br>
> > k_500_rkmax_8.scf::ENE : ********** TOTAL
ENERGY IN Ry =<br>
> > -43322.30312578<br>
> ><br>
> > Charge distance looks like it converges in both
cases. Note that<br>
> > whilst the two calculations have the same saved
name, they are in<br>
> > completely different CASE files. To outline my
procedure, I initially<br>
> > call,<br>
> ><br>
> > instgen -ask<br>
> ><br>
> > And define the moments as ‘u u u u u u u u n n
n n n n n n’ for a<br>
> > ferromagnetic calculation and ‘u u u u d d d d n
n n n n n n n’<br>
> > for a ferrimagnetic calculation.<br>
> ><br>
> > Then,<br>
> ><br>
> > init -b -sp -numk 500 -rkmax 8.00<br>
> ><br>
> > runsp -ec 0.0001 -cc 0.0001 -fc 1.0 -p -i 200<br>
> ><br>
> > I am at a loss as to what is going on and can’t
find anything in<br>
> > the mailing list to explain this. Any help on
this matter would be<br>
> > greatly appreciated.<br>
> ><br>
> > Regards,<br>
> ><br>
> > Charlie<br>
> > _______________________________________________<br>
> > Wien mailing list<br>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
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