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Many DFT codes use pseudopotentials to represent the electron-ion interaction (as do most plane-wave codes and in contrast to so-called "all-electron" programs).

There are several resources on the web to generate pseudopotentials in different formats and for different DFT codes. One of them is the program ATOM. Bellow is an example ot the ATOM input file for carbon.

       pg                  -- file generated from C ps file
        tm2
    C   ca 
     0.000     0.000     0.000     0.000     0.000     0.000
    1    4
    2    0     2.000     0.000    #2s
    2    1     2.000     0.000    #2p
    3    2     0.000     0.000    #3d
    4    3     0.000     0.000    #4f
   1.56000   1.56000   1.56000   1.56000   0.00000   0.00000

#23456789012345678901234567890123456789012345678901234567890      Ruler

My question is: how to generate a pseudopotential for a cation/anion?

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    $\begingroup$ I don't really know how to do it, but wouldn't one expect the net charge to be irrelevant to represent the inner core of an atom? $\endgroup$ May 18 '20 at 12:56
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Why would you want to generate a pseudopotential for a cation/anion? The pseudopotential is only for the inner core electrons. The only case where you'd want to do this is when the charge state of the system is so extreme that the inner shells are disturbed as well. (Also note that anions are ill-described by DFT so setting up an anion pseudopotential would be problematic.)

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    $\begingroup$ I asked the same thing. But I had a paper where one of the referees insist that as I used a single atom, it must be in ionic state, so, I have to generate a new pseudopotential to take into account the charge diference. $\endgroup$
    – Camps
    May 19 '20 at 16:54
  • $\begingroup$ If you only have a single atom, you don't need pseudopotentials; you can run a much more accurate calculation directly with an atomic approach... $\endgroup$ May 20 '20 at 11:31
  • $\begingroup$ There are 121 atoms. A nanotube and the atom that is put near it. $\endgroup$
    – Camps
    May 20 '20 at 13:06
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    $\begingroup$ Okay, then the reviewer's demand really doesn't make any sense! :D $\endgroup$ May 21 '20 at 11:25

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