The ABINIT Users Mailing List ( CLOSED )

[Anglade Pierre-Matthieu <anglade@gmail.com>]

Dear Thierry (and Damien),

I'm jumping on the wagon of charged system and bigdft : Is there some
variables usable from Abinit to help Bigdft converge a charged system
with open shells. For instance suppose you remove an electron from
water or whatever. My experience is that it takes forever to converge
with bigdft 1.2.0. I was in fact not able to reach the true ground
state of the system. Eventhough the calculation seemed converged
(1e-13 on WF). I guess there is some options to deal with that on the
wavelet code. But I didn't found them.

regards

PMA

On Tue, Mar 10, 2009 at 5:58 PM, Thierry Deutsch <thierry.deutsch@cea.fr> 
wrote:
> 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
> -----------------------------------------------------------------------
>
>



-- 
Pierre-Matthieu Anglade