[Pw_forum] Question about potential (pp tool)

[degironc]

If you are reading a psedopotential in the OLD fomat (not the UPF 
format) there is an array Vloc and then a number of
DeltaV_l, and then there is also a variable called lloc that specify 
which  l-component is considered as local.
Inside the PW code then  Vloc_at(r) = Vloc(r) + DeltaV_lloc(r) [this is 
the quantity that enters in Vbare referred to in pp.x] and the NON-LOCAL 
part is built  from DeltaV_l - DeltaV_lloc.
If the pseudopotential were used in the semilocal form (not in the KB 
form) different choices for  lloc would all coincide for
0<= l <=lmax ( max ang component in the pseudo) and only angular 
component correspondig to l > lmax would be affected... this should not 
have large effects (this form is not anymore implemented in PW).
In the KB fully non-local form different choices of lloc therefore 
produce slightly different pseudopotentials that  all gives the same 
results on the atomic configuration used for the KB projection and 
should behave similarly provided they do not have GHOST states.  Usually 
lloc=lmax (or lmax+1) would be the most "physical" choice but this is 
not always possible due to the ghosts problem above.
 
Using UPF format this little algebra has alredy been done in the 
pseudopotential file and Vloc_at above is given direclty in the PP_LOCAL 
field while the KB projections = DeltaV*Psi_atomic are given in the 
PP_BETA fields and lloc is not needed anymore.

Sorry if  this explanation confuses you again...

stefano

Lilia Boeri wrote:

>dear Stefano,
>
>thanks a lot. Reading another message that you wrote me some time ago, 
>I understand that when a psp is read from PWSCF one of the l components is 
>assumed as "local" potential, while the other channels are considered 
>non-local and obtained from the first by projection. Is this correct?
>
>If this is only a numerical trick, the results should not depend on which 
>channel I choose as "local", is this correct? 
>thanks,
>Lilia
>
>On Wed, 4 Oct 2006, degironc wrote:
>
>  
>
>>It is the total local potential which inside the core region is meaningless.
>>Only the region outside the core is "physical" .
>>stefano
>>
>>Lilia Boeri wrote:
>>
>>    
>>
>>>Dear PWSCF users,
>>>
>>>I am sorry for the somehow stupid question, but the more I think about it
>>>the more I get confused... The question is: what is exactly the "total"
>>>potential which is given by pp.x when plot_num is set to 1?
>>>The manual says:
>>>1=total potential V_bare+V_H + V_xc
>>>
>>>my question is: what is V_bare? Is it the local potential or some sort of
>>>total average potential?
>>>
>>>Thanks a lot,
>>>Lilia
>>>
>>>
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>>>      
>>>
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>>    
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