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My question is mainly one about consistency in the smearing method used for a standard "geometry relaxation + band structure (BS) + density of states (DOS)" set of calculations. This is a general query, but I make heavy reference to the Vienna Ab initio Simulation Package (VASP).

For gapped systems, I understand that the tetrahedron method (ISMEAR = -5 in VASP) is recommended for a high-quality DOS (Ref: the VASP wiki this paper). However, if I were to do a BS calculation with a line mode KPOINTS file such as

Line_mode KPOINTS file
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Line_mode
Reciprocal
0.0 0.0 0.0 ! \Gamma
0.3333333333333333 0.3333333333333333 0.0 ! K

0.3333333333333333 0.3333333333333333 0.0 ! K
0.5 0.0 0.0 ! M

0.5 0.0 0.0 ! M
0.0 0.0 0.0 ! \Gamma

the tetrahedron method would of course be incompatible and give the following error.

The linear tetrahedron method can not  be used with the KPOINTS file   |
|      (generation of strings of k-points)

In this case, it would be necessary, for example, to use Gaussian smearing (ISMEAR = 0 in VASP).

Hence, my concern is that we can't seem to consistently use the same smearing method for the entire "geometry relaxation (e.g. with ISIF = 3) + BS + DOS" set of calculations.

As the optimized geometry using both smearing methods is effectively indistinguishable within some small tolerance (based on my tests), my main question is if it is acceptable / standard practice to, for example, perform the geometry relaxation (and BS calculation) with Gaussian smearing (ISMEAR = 0) and only switch over to the tetrahedron method (ISMEAR = -5) for the DOS calculations (besides other changes like increasing the k-point density)?

Thank you.

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    $\begingroup$ It is common practice to switch from ISMEAR to -5 only for DOS calculation $\endgroup$ Oct 25, 2022 at 3:34
  • $\begingroup$ @Pranavkumar Do you think you can turn that comment into an answer, since this question has been taking up space in the unanswered queue for 7 months? Perhaps you can go into a bit more detail? Also CW Tan, if you have learned more about this over the last 7 months, feel free to write a self-answer! $\endgroup$ Jun 11, 2023 at 17:50

1 Answer 1

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tetrahedron smearing(ISMEAR=-5) is not suitable for ionic relaxation because it introduces broadening of electronic energy levels, which can lead to inaccurate force evaluations and unphysical atomic configurations in ionic systems. For DOS with sharp peaks, tetrahedron smearing provides more accurate descriptions.

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