Atom relaxation along cartesian z axis (NOT the direct lattice vector)

[nisazakiazahra_ulumuddin]

Dear All,

I have an orthorombic cell, where the lattice vectors are

5.0119748744 0.0 0.0
0.0 16.6852600789 0.0
0.0 7.5898730545 4.2747252576

and I need to do atomic position relaxation along the cartesian z-axis (perpendicular to the xy-plane), rather than along the c lattice vector.

If I orthogonalize the cell, it will create thousands of atoms, so this is unrealistic to run in VASP.

Does someone have a way to do this?

[pedro_melo]

Dear nisazakiazahra_ulumuddin,

I am not sure I understand what you are tying to do. Do you want your ions to only move along z, but the cell lattice vectors to remain constant? Or are the cell lattice vectors also supposed to change?

Could you post your POSTCAR here? It might help figuring out what can be done and how to do it.

Kind regards,
Pedro

[nisazakiazahra_ulumuddin]

Hi Pedro,

I have an orthorombic cell, attached here, and I want its atom positions to relax along the perpendicular direction to the xy-plane. In this context I will actually create a slab model derived from this orthorombic cell, and I will displace the upper half of the slab along the a-axis/x-axis in various increments (also called Generalized Stacking Fault Energy calculation). I then need VASP to geometrically optimize the structures where the atoms (positions) are relaxed only in the perpendicular direction to this slip motion.

In the default VASP setting, F F T will let the atoms relax along the c lattice vector, not the cartesian z-axis.

I struggled to attach the POSCAR so I paste it below:

POSCAR file written by OVITO Pro 3.10.6
1
5.0119748744 0.0 0.0
0.0 16.6852600789 0.0
0.0 7.5898730545 4.2747252576
Sm Co
6 18
Direct
0.0 0.0 0.0
0.0 0.1425999999 0.1425999999
0.0 0.8574000001 0.8574000001
0.5 0.642566661 0.142566661
0.5 0.357433339 0.857433339
0.5 0.5 0.0
0.5 0.9178000093 0.9178000093
0.5 0.0821999982 0.0821999982
2.5004148492e-05 0.5821749866 0.0821499825
0.2500250041 0.1678749919 0.4178499877
0.2500250041 0.3321749866 0.5821499825
0.7500250041 0.1678749919 0.4178499877
0.7500250041 0.3321749866 0.5821499825
0.0 0.4178333481 0.9178333481
0.75 0.6678333481 0.4178333481
0.75 0.832133313 0.582133313
0.2499749959 0.6678250134 0.4178500175
0.25 0.832133313 0.582133313
0.0 0.3333333333 0.3333333333
0.0 0.6666666667 0.6666666667
0.5 0.8333333333 0.3333333333
0.5 0.1666666667 0.6666666667
0.0 0.5 0.5
0.5 0.0 0.5

P.S. I do not need to relax the cell lattice vectors.