[CP2K:1757] Re: Total dipole via LOCALIZATION - bug?

[Fawzi Mohamed]

On 3-feb-09, at 12:22, Juerg Hutter wrote:

>
> Hi Fawzi
>
>> The thing my code did and is not done now is simply to remove jumps  
>> by
>> L/2*pi, and output also the finite derivative of the dipole, this
>> could also be added to the present code as an option.
>>
>> If you use the total dipole of a periodic system setting the  
>> reference
>> to COAC is not so useful, and does not allow you to remove the jumps
>> easily.
>
> Can you explain why the removal of jumps depends on the reference  
> point?
> If you use COAC there is only one non-zero term, meaning there is also
> one term that can jump. For all other cases both contributions can
> jump independently.
>
> Juerg

you are right, indeed the simple removal of jumps works also with COAC.
I was thinking that using an oscillating reference point might  
introduce a spurious signal.
Without the berry phase as long at the system is neutral the reference  
point has no importance, but if one treats only the electrons, the  
system is charged, and one has to take care how the ions+electrons  
system if brought back together (only for the whole system there is no  
problem).
Using the berry phase the thing should be the same, but I already flip- 
flopped a couple of times on it.
I would say that the thing is not immediately obvious for systems  
distributed on the whole cell, but it might well be that you are right  
(it makes sense for neutral systems).

Fawzi