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For studying a bulk supercell, after creating some vacuum in it, I'm confused about how to relax it.

With VASP, I can do relaxation using NSW = 0 and ISIF tag 2 or 3. Alternatively, I could set NSW=100 and with some value for ISIF (not sure what would be best).

A third option is to first relax the supercell, then after creating a vacuum, it is should be fine to select ISIF=0 for relaxation.

I am not sure which one of these is the best option or whether there is a better alternative.

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    $\begingroup$ Please watch the spaces in your INCAR file. It might only concern some versions of VASP, but I burned myself pretty badly with the INCAR file when I started doing calculations, because the entries were not read correctly. To be on the safe side, always include a space before and after the = (write NSW = 100 instead of NSW=100), otherwise the code may turn to default values instead of the specified ones. And do not use tabs! $\endgroup$
    – And
    Nov 29 '21 at 12:26
  • $\begingroup$ Thank you so much for sharing this useful information. $\endgroup$ Nov 29 '21 at 15:28
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The common feature of a surface is that interlayer distance changes near the surface. For relaxation of atom and calculating surface energy in vasp ISIF=2 and NSW=100 is correct option.

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