The ABINIT Users Mailing List ( CLOSED )

[Thierry Deutsch <thierry.deutsch@cea.fr>]

Difficult question...

Assume that we can calculate exactly the ground state of O + H far away 
each other.

What is the ground state of this system?

I guess it is O- and H+.
So there is a charge transfer even if you have no interaction. This is 
correct because we want the ground state and the oxygen is more 
electronegative than H.

I did the calculation with BigDFT (wavelet part of ABINIT) forcing the 
initial configuration to 1 electron to H. I found effectively H+ and O- 
(separation to 20 bohr).

I think it  is not related to functional because this comes from 
electrostatic effect.

Best Regards
6671011@163.com a écrit :
> 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
>
>
>
> ----------------------------------------------------------------------------------------------------
> 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
>
>
> ----------------------------------------------------------------------------------------------------
> 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
>
>   


--
-----------------------------------------------------------------------
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
-----------------------------------------------------------------------