12
$\begingroup$

I have some general questions about doing the structure relaxation of a thin film structure in VASP. I want to study the how the band structure evolves as we increase the number of layers of the material. The spin-orbit coupling (SOC) was included in the calculation, and I encounter the following question.

  1. Should I turn the ISYM = 0 to also change the shape of the unit cell during the structure relaxation?

  2. Should I include the SOC during the relaxation?

  3. I saw some people doing this structure relaxation will fix the bottom layer of the slab by using the selective dynamic option, when should I use this technique?

$\endgroup$
11
$\begingroup$

Should I turn the ISYM = 0 to also change the shape of the unit cell during the structure relaxation?

In essence, you are asking how to build a slab model. One special point is that you should add a large vacuum layer (here I assume that direction is along [001]). The relaxation of the slab model is limited to (100) and (010), so you can't change the shape. Namely, if want to use ISIF=3, you should modify the source file [constr_cell_relax.F] and re-compile your VASP.

Should I include the SOC during the relaxation?

In general, the SOC can be ignored in relaxation.

I saw some people doing this structure relaxation will fix the bottom layer of the slab by using the selective dynamic option, when should I use this technique?

When you study the surface science.

$\endgroup$
8
  • $\begingroup$ Thank you for your answer, Jack. May I ask further question about this ?So like what you said, the ISYM should be 2 during the relaxation procedure ? And the z-position of the atom ((thickness of the slab) should be fixed during the relaxation ? $\endgroup$ – JensenPang Jan 25 at 13:26
  • 1
    $\begingroup$ Although I would generally agree that SOC can usually be ignored in relaxations, there are actually a few examples of materials in which you get the incorrect structure/symmetry if you don't include SOC -- so it is always worth cross-checking. $\endgroup$ – ProfM Jan 25 at 13:33
  • $\begingroup$ @JensenPang If the lattice constant is identified, of course, you can relax with ISIF=2. For slab calculation, you can first fix the lattice constant by relaxing a bulk structure. $\endgroup$ – Jack Jan 25 at 13:48
  • $\begingroup$ @ProfM Could you detail this with an answer? $\endgroup$ – Jack Jan 25 at 13:49
  • $\begingroup$ @Jack I am not sure this is worth a full answer, but here are two papers (disclaimer: I am a co-author in one): iopscience.iop.org/article/10.1088/2515-7639/ab4c2b journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.117701 $\endgroup$ – ProfM Jan 25 at 14:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.