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Dear Thierry,

I'd like to question further on this issue with an example.

For a system with two atoms: H and O, which are separated by very large
distance (say several hundred Angstroms). Almost all of the present programs
show that there is a charge transfer between them. Experimentally, however, it
is absolutely wrong.

Someone said this problem is beyond the Born-Oppenheimer approximation. Is 
that
true?


Sincerely,
Guangfu Luo



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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

-----------------------------------
Thierry Deutsch Laboratoire de simulation atomistique (L_Sim) 
INAC/SP2M Tél:(33) 04 38 78 34 06
C.E.A.Grenoble Fax:(33) 04 38 78 51 97
17, Avenue des Martyrs mailto:Thierry.Deutsch@cea.fr
38054 GRENOBLE CEDEX 9 FRANCE http://inac.cea.fr/L_Sim


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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