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Let's say I optimized geometry with PBE+D3, does it matter if I make single point bandstructure calculation with just PBE or PBE+D3 since D3 is a additive method.

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It doesn't matter. The self-consistent calculation will use the Hamiltonian constructed from the relaxed structure, in which the D3 has been applied and should not be considered again.

Take bilayer MoSe2 as an example:

enter image description here

This structure is optimized with PBE+D3 using the VASP package. With this relaxed structure, I have calculated the band structure with and without the consideration of D3 in the INCAR file. One can not see any difference between the two band structures.

enter image description here

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  • $\begingroup$ The visual for this is very good. $\endgroup$ – Tristan Maxson Sep 17 at 14:32
  • $\begingroup$ I am not very sure about "It doesn't matter". If the system is sensible to D3 corrections, the results shouldn't be different? Maybe in your example, the bands are the same just because MoSe2 is not sensible to D3 correction... $\endgroup$ – Camps Sep 17 at 17:34
  • $\begingroup$ @TristanMaxson Thanks. $\endgroup$ – Jack Sep 18 at 11:07
  • $\begingroup$ @Camps I have supported a simple argument. $\endgroup$ – Jack Sep 18 at 11:08
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    $\begingroup$ @Camps We are talking about a single point calculation, geometric effects do not come into play unless we perform a relaxation. See my answer for a clarification (I extended past Jack's answer to the exact situation you are talking about), When calculating a band structure, you can turn off the D3 correction to save time since it does not need to be calculated. This is the real application of this knowledge (even if its a minor calculation to make). $\endgroup$ – Tristan Maxson Sep 18 at 17:09
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A PBE vs PBE+D3 calculation will have the same band structure if the same geometry is used. If the geometry is optimized, however, they can differ but the D3 correction does not directly influence the band structure just the geometry.

You can validate this method by considering that these corrections can often be done by an external step such as combining VASP with D3 using ASE rather than VASP's internal tools. To VASP, nothing about these calculations is different, the correction happens afterward.

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