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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

Thierry is quite right (use the Poisson solver and spin).

I would add that in abinit you can never be sure that the electron will go to a particular orbital if you are doing a self-consistent calculation. It will go wherever it needs to to minimize the energy. Looking at the orbitals for a neutral system and then taking an electron into or out of a state by using occ will not work unless the system really does prefer that specific charge state (this is unlike atomic orbitals where you can constrain the n^th state localized on an atom to be empty or full). In simple molecular cases you can be pretty certain of the state ordering and thus of the charge state you will get with, e.g., 

occ

1 1 0 0 0
1 1 1 0 0

but in general it's less determined. This is normal, as the lowest energy state for a given configuration is fixed, and that is what abinit will find. You can also do non-SC calculations, and populate the states as you wish, but it depends what you want to get out: the total energy is no longer well defined.

Matthieu

On Tue, Mar 10, 2009 at 1:37 PM, Thierry Deutsch <thierry.deutsch@cea.fr> wrote:

Hi,

      ABINIT can use periodic Poisson solver based on plane waves or Poisson solver for isolated system. The last one is based on wavelet (exactly interpolating scaling functions). If you use plane waves to represent wavefunctions, there is no difference for neutral systems.
In this case, the dependence of the kinetic term versus the size of the box is predominant (plane waves delocalize).

For charged system, (as H3O+), the Poisson solver based on wavelet is more accurate and uses very very less memory.

If you calculate NH3 and H3O+ together in a big box, you only need to specify the total charge. The system should localize an electron on H3O.
Because you have molecules, you should have 1 for occupied states (spin-polarized case).

An alternative is also to use the whole wavelet part of ABINIT... The advantage is to use less memory.

Best Regards,

Thierry


Quan Phung Manh a écrit :

After calculating NH4+, I have more question.
If I have a big box with a molecule NH3 and an ion H3O+ for example. How can I simulate it? How can I sure that the charge + is in H3O, not NH3? Can I solve this by using occ?

Best regarded

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Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
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