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priyo_adhikary
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#1
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by priyo_adhikary » Wed Apr 29, 2026 5:53 pm
Hi,
I am using VASP 6.6 for a triclinic/non-orthorhombic cell and would like to relax only the inplane lattice degrees of freedom while keeping the out of plane direction fixed. I was considering LATTICE_CONSTRAINTS = .TRUE. .TRUE. .FALSE.
ISIF = 3. For an orthorhombic cell, I understand that LATTICE_CONSTRAINTS = .TRUE. .TRUE. .FALSE. keeps the third lattice parameter fixed. However, for a triclinic cell, does this constraint keep only the third lattice vector fixed?
In particular, is it correct to say that this setting keeps [c,\alpha,\beta ] fix and change [a,b,\gamma]?
INCAR.zip
.
Thanks
Priyo
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henrique_miranda
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#2
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by henrique_miranda » Thu Apr 30, 2026 9:40 am
Hi,
I fear this is not the case.
In this page you can find a very detailed explanation of this tag and I think it does answer your question:
https://vasp.at/wiki/LATTICE_CONSTRAINTS
If it still does not answer your question don't hesitate to ask what is not clear.
I think the easiest way to accomplish what you want is to use a different choice of lattice vectors where the vector you want to keep fixed is orthogonal to the other in-plane vectors.