[Wien] Fixing Atomic Positions During Geometry minimization:constraint failed!

[Peter Blaha]

mixer tries to keep the center of mass constant (to avoid that all atoms 
move in some direction, although their distances are in equilibrium).

At the moment, you cannot switch this off, although it would make sense 
if an atom is constrained in a certain direction (Laurie: I know, you 
don't like these constraint positions, but it might be a valuable 
modification to use the center of mass in a certain direction only if no 
positions are constrained).

In general I would NOT recommend to fix only one side of the slab, at 
least not if you have mirror symmetry along z. You have then a 
calculation with a relaxed and an unrelaxed surface !

What makes sense, is to fix the middle layers of a slab....

Am 07.05.2025 um 10:21 schrieb Hadjer MEZIANI via Wien:
> Dear wien2k users,
> I am performing geometry minimization (MSR1a) of the TiO₂ surface to 
> relax the top layer while keeping the bottom layers fixed, using 
> WIEN2k_24.1. I followed these steps:
> 1-Generate struct
> 2- init-lapw
> 3-mini.positions(w2web) and i edit case.inM after that i run pairhase; 
> copy .minpair to .minrestart and delete .min_hess.
> 4- run scf with activate optimize positions(MSR1a) with -fc 20.
> I constrained the atoms in the bottom layers by setting `delta=0`, but 
> these atoms are still displaced during the minimization.
> 
> .inM file in the following way:
> PORT 2.00 0.35 2.00    # PORT/NEWT;  tolf, Initial Trust Radius, tolfa
> 0.0 0.0 0.0 1.0   #Atom    1 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    2 Generated by pairhess
> 1.0 1.0 1.0 1.0   #Atom    3 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    4 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    5 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    6 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    7 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    8 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom    9 Generated by pairhess
> 1.0 1.0 1.0 1.0   #Atom   10 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   11 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   12 Generated by pairhess
> 1.0 1.0 1.0 1.0   #Atom   13 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   14 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   15 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   16 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   17 Generated by pairhess
> 1.0 1.0 1.0 1.0   #Atom   18 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   19 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   20 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   21 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   22 Generated by pairhess
> 1.0 1.0 1.0 1.0   #Atom   23 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   24 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   25 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   26 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   27 Generated by pairhess
> 1.0 1.0 1.0 1.0   #Atom   28 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   29 Generated by pairhess
> 0.0 0.0 0.0 1.0   #Atom   30 Generated by pairhess
> For example, atom 1 has changed position even though it was fixed in 
> `.inM`. See output:
> --- atom dependend parameter POS -----------
> in  1 files:
> :POS001: ATOM   -1 X,Y,Z = 0.50000 0.00000 0.04398  MULT= 1  ZZ= 22.000  Ti
> :POS001: ATOM   -1 X,Y,Z = 0.50000 1.00000 0.04397  MULT= 1  ZZ= 22.000  Ti
> :POS001: ATOM   -1 X,Y,Z = 0.50000 1.00000 0.04396  MULT= 1  ZZ= 22.000  Ti
> :POS001: ATOM   -1 X,Y,Z = 0.50000 1.00000 0.04389  MULT= 1  ZZ= 22.000  Ti
> :POS001: ATOM   -1 X,Y,Z = 0.50000 0.00000 0.04382  MULT= 1  ZZ= 22.000  Ti
> :POS001: ATOM   -1 X,Y,Z = 0.50000-0.00000 0.04337  MULT= 1  ZZ= 22.000  Ti
> ......
> My question is: how can i keep positions of these atoms unchanged during 
> structure minimzation!
> Any suggesting are highly welcome
> Thank you in advence
> M. Hadjer
> 
> 
> 
> 
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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email: peter.blaha at tuwien.ac.at
WWW:   http://www.imc.tuwien.ac.at      WIEN2k: http://www.wien2k.at
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