[ase-users] about charged slab calculation

[Huang Bing]

They say that it's not possible to do charged slab calculation in vasp,
so i wonder if these kind of calculation is valid or not in Dacapo.
see this url
http://cms.mpi.univie.ac.at/vasp-forum/forum_viewtopic.php?4.2463
<http://cms.mpi.univie.ac.at/vasp-forum/forum_viewtopic.php?4.2463>for
detail, or have a look at the text below, which is copied directly
from the contents in that link:

 <http://cms.mpi.univie.ac.at/vasp-forum/forum_viewtopic.php?4.2463>>I have
a question. Is it possible to optimize charged unit cell, for example,
>if I want to investigate adsorption of charged species on neutral surface?
>If yes, where can I read about method, possible errors, etc?
>Thank you in advance.

Here is the admin's reply:

a) on charged systems in general, please have a look in the manual
    (chapter multipole corrections)
b) Actually, you MUST NOT set the number of electrons manually for
    a slab calculation. I.e., when you calculate the surface+adsorbate
   system, you are not allowed to select a specific charge state for the
   adsorbate by increasing the number of electrons manually. Specific
   charge state calculations make sense only in 3d systems and for
   cluster calculations.  The electrostatic energy of such a slab is
    however only conditionally convergent and in practice even infinite
    (BASIC, BASIC ELECTROSTATICS).
   Only if the calcuations are done properly, i.e., if your slab is large
   enough and the lateral dimension (x,y) of your surface is large enough
    (test for the necessary 2D dimension, the total energy has to converge
    to the correct value with (1/(distance between the charged species) )
   the energy should converge to the proper value, i.e. the adsorbed species
 should acquire the correct charge state (then, it is acquired
automatically).

Any comments is highly appreciated!
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