<div dir="ltr">Let me clarify slightly my comment about symmetry -- as I realized the explanation (I think) and can also suggest something that might help.<div><br></div><div>First, concerning symmetry the explanation is I believe simple. If the problem has a real symmetry operation such as inversion which is being removed, then the Jacobian at the solution has zero's for charge disturbances that break this symmetry. Because of this noise due to numerical accuracy has a large effect, and almost certainly one has to tighten the convergence criteria particularly -cc. You can monitor this by looking at the :PUPXXX values in case.scfm and look how well the forbidden reflections have converged to zero.</div><div><br></div><div>Second, do not be surprised about numerical issues. While the calculations are done in double precision, there are many large sums and in some cases double sums, and also numerical integrations/differentiation. Any large sum or numerical integration/differentiation in general reduces the numerical accuracy. Hence even though double precision has an accuracy of 1D-15 the sum may only be accurate to 1D-10 or even 1D-7. Also, the Intel ifort compiler will reduce the numerical accuracy for speed if one is not careful.</div><div><br></div><div>One thing that may help is to increase the oversampling in case.in0 for VXC, both that of the PW's and of the CLMs. A standard test is to use LDA and see if the problem goes away, since oversampling is much less relevant for this.</div><div><br></div><div>Of course your problem may have nothing to do with any of this....<br><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Nov 27, 2017 at 8:07 AM, Jaroslav Hamrle <span dir="ltr"><<a href="mailto:hamrle@karlov.mff.cuni.cz" target="_blank">hamrle@karlov.mff.cuni.cz</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<div class="gmail-m_-7816783121432242030moz-cite-prefix">
<p>Dear all,</p>
<p>thank you for your comments:</p>
<p>1) </p><span class="gmail-">
<blockquote type="cite">
<pre>Did you use a Gamma centered k mesh (and enough k points)</pre>
</blockquote>
<br>
</span><p>I have checked that the same inequality in MLD, appears both when k-points are shifted or not shifted. So, influence of shift of k-points can be ruled out.</p>
<p>I have 30x30x30 k-points, which should be enough. When using 46x46x46 k-mesh, the MLD inequality is reduced by about factor two, but still present. Even when using very fine k-mesh (90x90x90) for optical calculation, the inequality persists.<br>
</p>
<p><br>
</p>
<p>2) <br>
</p><span class="gmail-">
<p></p>
<blockquote type="cite"><span style="color:rgb(0,0,0);font-size:12.8px">In some cells shifting the k-point origin with MSR1a leads to slightly unbalanced forces which are hard to converge to the "right" symmetric result. If the forces are slightly off, this
is an indication that the density is also slightly off. Exactly why this occurs I do not know, I suspect very soft modes associated with numerical errors in finite arithmetic.</span></blockquote>
<br>
</span><p>Well, for me it is hard to believe, that the problem can originates from numerical error. The MLD inequality creates sort-of ghost peaks in MLD spectra which for bcc Fe are very stable at positions at 4.8 and 6 eV for different calculation details (as different
k-mesh, presence/absence of spin-orbit, shifted/non-shifted k-mesh). Under all those changes in the calculations, the position of ghost peaks remains very stable, just their amplitudes varies. Also, if problem would be just numerical one, why ghost peaks are
not present in simple cubic or fcc calculations?<br>
</p>
<p><br>
</p>
<p>3)<br>
</p><span class="gmail-">
<blockquote type="cite"><br>
It is instructive to repeat the calculation without SO and see how big the difference between sig_xx and sig_yy (for any M direction) is then.
</blockquote>
<br></span>
I tried to calculate various combinations of structure, (with/without SO or sp) using full (non-magnetic) bcc symmetry, or bcc symmetry reduced by presence of magnetization (i.e. it means reduction of symmetry + new k-mesh as generated by initso).<br>
In case of spin-polarized calculations without SO, the ghost MLD peaks appear when going from full bcc symmetry to bcc symmetry reduced by magnetization.<br>
<br>
<br>
<p></p>
<table cellspacing="0" border="0">
<colgroup width="312"></colgroup><colgroup width="85" span="3"></colgroup>
<tbody>
<tr>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left" height="17">
<br>
</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
nosp+noso</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
sp+noso</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
sp+so</td>
</tr>
<tr>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left" height="17">
bcc full symmetry without magnetization</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
OK</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
OK</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
X</td>
</tr>
<tr>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left" height="17">
bcc symmetry reduced by magnetization</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
?</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
ghosts</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
ghosts</td>
</tr>
<tr>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left" height="17">
(fcc or simple cubic) reduced by magnetization<br>
</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
?</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
OK</td>
<td style="border-width:1px;border-style:solid;border-color:rgb(0,0,0)" align="left">
OK</td>
</tr>
</tbody>
</table>
<p></p>
<p></p>
<br>
<br>
<br>
Therefore it seems to me that the ghost MLD peaks appear when symmetry is reduced in the bcc structure. It seems that SO coupling is not important in this problem.<br>
It is the lower symmetry itself, which creates the MLD inequality (ghost MLD peaks).<br>
<br>
For example, can there be some small problem with generation of k-mesh or related symmetry in bcc+magnetization case?<br>
<br>
<br>
Thank you for your help<span class="gmail-"><br>
With my best regards<br>
Jaroslav<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br></span><div><div class="gmail-h5">
On 26/11/17 18:51, Laurence Marks wrote:<br>
</div></div></div>
<blockquote type="cite"><div><div class="gmail-h5">
<div dir="ltr"><span style="color:rgb(0,0,0);font-size:12.8px">I will third the comment that not using a shifted cell might be important (might). In some cells shifting the k-point origin with MSR1a leads to slightly unbalanced forces which are hard to converge
to the "right" symmetric result. If the forces are slightly off, this is an indication that the density is also slightly off. Exactly why this occurs I do not know, I suspect very soft modes associated with numerical errors in finite arithmetic.</span>
<div style="color:rgb(0,0,0);font-size:12.8px"><br>
</div>
<div style="color:rgb(0,0,0);font-size:12.8px">N.B., Wien2k is quite good with these numerical errors. I've noticed that Vasp calculations that collaborators have done often have much larger symmetry breaking.</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sun, Nov 26, 2017 at 11:39 AM, Karel Vyborny <span dir="ltr">
<<a href="mailto:vybornyk@fzu.cz" target="_blank">vybornyk@fzu.cz</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
I suppose that this does not have to do (much) with centering the mesh.<br>
My guess based on other QMO calculations is that some contributions to<br>
mat. els. of e.g. vx*vx from different parts of the BZ don't cancel<br>
(numerically) even if they actually should.<br>
<br>
It is instructive to repeat the calculation without SO and see how big the<br>
difference between sig_xx and sig_yy (for any M direction) is then.<br>
<br>
Cheers,<br>
<br>
Karel<br>
<br>
<br>
--- x ---<br>
dr. Karel Vyborny<br>
Fyzikalni ustav AV CR, v.v.i.<br>
Cukrovarnicka 10<br>
Praha 6, CZ-16253<br>
tel: +420220318459<br>
<br>
<br>
On Sun, 26 Nov 2017, Fecher, Gerhard wrote:<br>
<br>
> There was a recent discussion on magnetic anisotropy, With a remark by Peter,<br>
> Did you use a Gamma centered k mesh (and enough k points)<br>
><br>
> Ciao<br>
> Gerhard<br>
><br>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:<br>
> "I think the problem, to be quite honest with you,<br>
> is that you have never actually known what the question is."<br>
><br>
> ==============================<wbr>======<br>
> Dr. Gerhard H. Fecher<br>
> Institut of Inorganic and Analytical Chemistry<br>
> Johannes Gutenberg - University<br>
> 55099 Mainz<br>
> and<br>
> Max Planck Institute for Chemical Physics of Solids<br>
> 01187 Dresden<br>
</blockquote>
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<pre class="gmail-m_-7816783121432242030moz-signature" cols="72">--
------------------------------<wbr>------------------------------<wbr>------
Mgr. Jaroslav Hamrle, Ph.D.
Institute of Physics, room F232
Faculty of Mathematics and Physics
Charles University
Ke Karlovu 5
121 16 Prague
Czech Republic
tel: +420-95155 1340
email: <a class="gmail-m_-7816783121432242030moz-txt-link-abbreviated" href="mailto:hamrle@karlov.mff.cuni.cz" target="_blank">hamrle@karlov.mff.cuni.cz</a>
------------------------------<wbr>------------------------------<wbr>------ </pre>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><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 href="http://www.numis.northwestern.edu" target="_blank">www.numis.northwestern.edu</a> ; <span style="font-size:12.8px">Corrosion in 4D: </span><a href="http://MURI4D.numis.northwestern.edu" style="font-size:12.8px" target="_blank">MURI4D.numis.northwestern.edu</a><div><span style="font-size:12.8px">Partner of the CFW 100% program for gender equity, </span><a href="http://www.cfw.org/100-percent" style="font-size:12.8px" target="_blank">www.cfw.org/100-percent</a></div><div>Co-Editor, Acta Cryst A</div></div></div></div></div></div></div></div></div></div></div>
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