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Dear VASP developers,

I am wondering whether VASP can create a dummy (or "ghost") atom, i.e., one without electrons / basis sets. This question has been raised in a previous post (forum/viewtopic.php?t=4186), but has not yet been answered. Thank you for your time!

Sincerely,
Tian Hua

Hi,

There is apparently some empty spheres option, but mostly related to the DOS, as discussed at https://vasp.at/forum/viewtopic.php?t=19412. What would you like to do with empty spheres?

Dear Dr. Tran,

Thank you for your reply. However, my calculation is not related to DOS. What I aim to do is directly calculate the solvation free energy of an ion pair in aqueous solutions form first principles molecular dynamics simulations coupled with thermodynamic integration, in which the interactions between the ion pair and water molecules are gradually turned off. Therefore, I need to set the atoms in the ion pair as dummy (or "ghost") atoms. I have noticed that VASP can achieve this when using machine learning force fields (Jinnouchi et al., 2020, Physical Review B 101, 060201); however, on-the-fly MLFF is difficult to apply to aqueous solutions with many elements. I am wondering if dummy (or "ghost") atoms can be created at the DFT level.

Thank you for your time, and I am looking forward to your reply.
Sincerely,
Tian Hua

Hi,

Actually, colleagues told me that there was, in the past, a possibility to have empty spheres (there are a few "empty spheres" in poscar.F). However, this feature has not been maintained and is probably not working anymore.

Dear Dr. Tran,

Thank you very much for your reply. It is unfortunate that this feature has not been maintained. From my point of view, dummy (or "ghost") atoms are also useful in many calculations, such as free energy calculations based on thermodynamic integration. I would personally recommend considering the restoration of this feature in a future version of VASP.

Thank you again for your time in addressing my question.
Sincerely,
Tian Hua