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<p>Thank you so much Laurence for this explanation which definitely
enlight my understanding! <br>
</p>
<p>Could you just give me more hints. What do you mean by "fixed
point solution" when you are speaking about the spins? <br>
</p>
<p>Brainstorming session:<br>
</p>
<p>I am a chemist but I can propose an idea without a clear
understanding! The rotations are non-linear and we should find a
way to express them in such a way to be linear. <br>
</p>
<p>Is a Fourier transform (or fractional Fourier transform or
something related) useful in such a case? </p>
<p>Cheers</p>
<p>Xavier<br>
</p>
<p><br>
</p>
<p><br>
</p>
<br>
<div class="moz-cite-prefix">Le 01/11/2018 à 17:19, Laurence Marks a
écrit :<br>
</div>
<blockquote
cite="mid:CANkSMZCa4BF6tYT+QvZD49n5-n4KTPhNv_Qmw+HdTL0Tx+13cw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000">Quite a
few things are going on "Under the hood" in these systems, so
let me explain a little.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000">For heavy
atoms with large RMTs the initial pseudocharge (PW density
inside the RMTs) from dstart is quite bad. In addition, unless
you are careful to chose a "good" initial spin state in
case.inst, the spins can be quite far from the fixed point
solution. While it might appear that the density and energy
(:DIS and :ENE) are oscillating, in reality the pseudocharge
and the spin/orbital moments are rotating slowly in a
N-Dimensional space. Rotations are non-linear, and the mixer
(all versions in all DFT codes to my knowledge) use linear
expansions. It can therefore take a long time for these
rotations tocomplete. What you will often see if you look at
the pseudocharge (grep :CPC in 18.1, the pseudocharge was not
monited in earlier versions as its role was not known) you
will often see that it is slowly "walking" -- similarly the
spin moments etc.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000">When you
add SOC and/or +U (or -eece) there will be large rotations of
the spins and/or spin moments.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;color:#000000">In an
ideal world some transformation would be applied to the Wien2k
variables to separate the pseudocharge and convert the
rotations to linear variables. I do not know how to do this,
and simple ideas such as using the sum and difference of spins
don't work. (As expected, since this is a linear
transformation.) I am open to (mathematical)
suggestions/inspirations. It has to be math not fudge -- the
mixer only works when the math is right!</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Thu, Nov 1, 2018 at 9:34 AM Xavier Rocquefelte
<<a moz-do-not-send="true"
href="mailto:xavier.rocquefelte@univ-rennes1.fr">xavier.rocquefelte@univ-rennes1.fr</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">I have
exactly the same experience. It is really a matter of cooking
to <br>
my point of view and strongly depends on the system and what
is <br>
happening at the Fermi level.<br>
<br>
In my case I am using DFT+U+SOC for such systems. The hubbard
term <br>
indeed allows to separate the 4f states. However, the SOC is
also <br>
essential and leads to large effects in these systems.<br>
In the case of HoPtBi, all the elements requires SOC. In
addition it is <br>
an intermetallic compound, meaning that you have both
localized and <br>
delocalized electrons!<br>
<br>
Did you try the following procedure:<br>
- DFT+SOC in a self-consistent manner<br>
- DFT+SOC+U on top of the first calculation<br>
<br>
Sometimes the lift of degeneracy due to SOC is sufficient to
converge <br>
more efficiently DFT+SOC and then after DFT+SOC+U. And
sometimes it is <br>
the other way around;)<br>
<br>
Best wishes<br>
Xavier<br>
<br>
<br>
-- <br>
------------------------<br>
Institut des Sciences Chimiques de Rennes (ISCR)<br>
Univ Rennes - CNRS - UMR6226, France<br>
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<div dir="ltr">
<div dir="ltr"><span style="font-size:12.8px">Professor
Laurence Marks</span><br>
</div>
<div dir="ltr"><span style="font-size:12.8px">"Research
is to see what everybody else has seen, and
to think what nobody else has thought", </span><span
style="font-size:12.8px">Albert Szent-Gyorgi</span><br>
<a moz-do-not-send="true"
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target="_blank">www.numis.northwestern.edu</a> ; <span
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------------------------
Institut des Sciences Chimiques de Rennes (ISCR)
Univ Rennes - CNRS - UMR6226, France
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