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I am trying to understand the function of dipole correction in DFT. I find that there are two examples related to this topic on the VASP wiki.
The first case is about CO on Ni 111 surface
The input INCAR file is :

 general:
   ENMAX = 400
   SYSTEM = CO adsorption on Ni(111)
   ISMEAR = -5
   ALGO= Fast

 LDOS:
   LORBIT = 11

 workfunction:
   IDIPOL=3
   LDIPOL= .TRUE.
   LVHAR = .TRUE.
#  LVTOT = .TRUE.

enter image description here

The second case is about Adsorption of H2O on TiO2
The input INCAR file is :

SYSTEM   = H2O_TiO2
ENMAX    = 400
ISMEAR   =  2
SIGMA = 0.05
EDIFF = 1e-6
EDIFFG = -0.05
IBRION = 2
POTIM = 0.5
NSW = 200

enter image description here

Apparently, the slabs of these two cases are both asymmetric, but it seems that the second case doesn't set dipole correction.
As far as I understand, when the slab model is asymmetric, I should always use dipole correction. My question is:
When should I use dipole correction?

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With a large enough vacuum, you don't need a dipole correction as badly to get good results. Sometimes the correction can cause convergence issues or problems with single steps giving incorrect energies.

The second calculation looks like a geometry optimization, so maybe this was done to improve stability; a dipole correction should be applied after converging the structure, but its not critical beforehand.

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  • $\begingroup$ May I please clarify the point on structure convergence? The VASP Wiki states that one of the key advantages of the dipole correction is that "leading errors in the forces are corrected", giving me the impression that it is important for accurately relaxed geometries. Perhaps the tutorial examples given are simplified for educational purposes? Or could it be that including dipole corrections for geometry optimizations leads to problematic convergence issues that we might as well avoid it at the cost of greater accuracy? Thanks. $\endgroup$
    – CW Tan
    Oct 26, 2022 at 13:07
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    $\begingroup$ Dipole corrections in my experience can sometimes cause VASP to be unstable during the geometry optimization (occasionally the routine fails for some materials). Converging the calculation without the dipole correction and then adding it at the end often doesn't even add any extra geometric steps, just a single point calculation (the forces remain converged). $\endgroup$
    – Tristan Maxson
    Oct 26, 2022 at 15:26

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