There is no option to perform this directly in Elk.
Setting latvopt=1 with task=2 will perform a full, symmetry-preserving lattice optimisation. Iso-volumetric optimisation can be performed with latvopt=2.
You can constrain atomic positions by making the species mass negative. This will zero the forces for that species.
Failing this, you can perform the optimisation manually by scaling a and b and fitting the resulting energy curve to a suitable function of a or b.
Regards,
Kay.
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how to perform the relaxation for the 2d materials(fix the c direction lattice and relax the a and b lattice)
There is no option to perform this directly in Elk.
Setting latvopt=1 with task=2 will perform a full, symmetry-preserving lattice optimisation. Iso-volumetric optimisation can be performed with latvopt=2.
You can constrain atomic positions by making the species mass negative. This will zero the forces for that species.
Failing this, you can perform the optimisation manually by scaling a and b and fitting the resulting energy curve to a suitable function of a or b.
Regards,
Kay.