<div dir="auto"><div>Depending upon which version is used the center of mass fixing may be inactive when atoms are fixed, which is why I asked about that. Plus the other questions, as some of the procedure used does not seem right.</div><div><br></div><div data-smartmail="gmail_signature">___<br>Emeritus Professor Laurence Marks (Laurie)<br>Department of Materials Science and Engineering, Northwestern University<br><a href="http://www.numis.northwestern.edu">www.numis.northwestern.edu</a><br>"Research is to see what everybody else has seen, and to think what nobody else has thought" Albert Szent-Györgyi</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Wed, May 7, 2025, 03:36 Peter Blaha <<a href="mailto:peter.blaha@tuwien.ac.at">peter.blaha@tuwien.ac.at</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">mixer tries to keep the center of mass constant (to avoid that all atoms <br>
move in some direction, although their distances are in equilibrium).<br>
<br>
At the moment, you cannot switch this off, although it would make sense <br>
if an atom is constrained in a certain direction (Laurie: I know, you <br>
don't like these constraint positions, but it might be a valuable <br>
modification to use the center of mass in a certain direction only if no <br>
positions are constrained).<br>
<br>
In general I would NOT recommend to fix only one side of the slab, at <br>
least not if you have mirror symmetry along z. You have then a <br>
calculation with a relaxed and an unrelaxed surface !<br>
<br>
What makes sense, is to fix the middle layers of a slab....<br>
<br>
Am 07.05.2025 um 10:21 schrieb Hadjer MEZIANI via Wien:<br>
> Dear wien2k users,<br>
> I am performing geometry minimization (MSR1a) of the TiO₂ surface to <br>
> relax the top layer while keeping the bottom layers fixed, using <br>
> WIEN2k_24.1. I followed these steps:<br>
> 1-Generate struct<br>
> 2- init-lapw<br>
> 3-mini.positions(w2web) and i edit case.inM after that i run pairhase; <br>
> copy .minpair to .minrestart and delete .min_hess.<br>
> 4- run scf with activate optimize positions(MSR1a) with -fc 20.<br>
> I constrained the atoms in the bottom layers by setting `delta=0`, but <br>
> these atoms are still displaced during the minimization.<br>
> <br>
> .inM file in the following way:<br>
> PORT 2.00 0.35 2.00 # PORT/NEWT; tolf, Initial Trust Radius, tolfa<br>
> 0.0 0.0 0.0 1.0 #Atom 1 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 2 Generated by pairhess<br>
> 1.0 1.0 1.0 1.0 #Atom 3 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 4 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 5 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 6 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 7 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 8 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 9 Generated by pairhess<br>
> 1.0 1.0 1.0 1.0 #Atom 10 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 11 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 12 Generated by pairhess<br>
> 1.0 1.0 1.0 1.0 #Atom 13 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 14 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 15 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 16 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 17 Generated by pairhess<br>
> 1.0 1.0 1.0 1.0 #Atom 18 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 19 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 20 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 21 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 22 Generated by pairhess<br>
> 1.0 1.0 1.0 1.0 #Atom 23 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 24 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 25 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 26 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 27 Generated by pairhess<br>
> 1.0 1.0 1.0 1.0 #Atom 28 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 29 Generated by pairhess<br>
> 0.0 0.0 0.0 1.0 #Atom 30 Generated by pairhess<br>
> For example, atom 1 has changed position even though it was fixed in <br>
> `.inM`. See output:<br>
> --- atom dependend parameter POS -----------<br>
> in 1 files:<br>
> :POS001: ATOM -1 X,Y,Z = 0.50000 0.00000 0.04398 MULT= 1 ZZ= 22.000 Ti<br>
> :POS001: ATOM -1 X,Y,Z = 0.50000 1.00000 0.04397 MULT= 1 ZZ= 22.000 Ti<br>
> :POS001: ATOM -1 X,Y,Z = 0.50000 1.00000 0.04396 MULT= 1 ZZ= 22.000 Ti<br>
> :POS001: ATOM -1 X,Y,Z = 0.50000 1.00000 0.04389 MULT= 1 ZZ= 22.000 Ti<br>
> :POS001: ATOM -1 X,Y,Z = 0.50000 0.00000 0.04382 MULT= 1 ZZ= 22.000 Ti<br>
> :POS001: ATOM -1 X,Y,Z = 0.50000-0.00000 0.04337 MULT= 1 ZZ= 22.000 Ti<br>
> ......<br>
> My question is: how can i keep positions of these atoms unchanged during <br>
> structure minimzation!<br>
> Any suggesting are highly welcome<br>
> Thank you in advence<br>
> M. Hadjer<br>
> <br>
> <br>
> <br>
> <br>
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<br>
-- <br>
-----------------------------------------------------------------------<br>
Peter Blaha, Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna<br>
Phone: +43-158801165300<br>
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</blockquote></div>