[Pw_forum] average potential

[Lorenzo Paulatto]

Dear Marcello,
I'll try to answer as correctly as possible, but I'm not checking the code  
for each point, so there could be some minor discrepancy with reality.

In data 20 agosto 2009 alle ore 16:01:58, Marcello Rosini  
<marcello.rosini at unimore.it> ha scritto:
> 1. In pp.x, what is the V_bare?

the superposition of the local potentials from the pseudopotentials. I.e.  
the descreened potential of the ions. It may contain some other piece,  
though, in some specific case (maybe the jigsaw potential, but that's easy  
to spot).

> 2. when summing and averaging the total local potential I expect to find
> a zero average. This does not happen, is my procedure wrong?

Not really, the average of the *total* potential has to be zero. But this  
is only enforced when the total potential is computed. Actually, I'm not  
even sure that's what happening, see point 4.

> 3. Is pw.x able to print somewhere the total local potential in k-space,
> V(G)? how should I do?

In module scf there is the object "v" which is a derived type.  
rho%of_g(ngm,nspin) is what you are looking for. You can also grab it from  
v_of_rho.f90 as soon as it is computed.


> 4. Is it true for pw.x V(G=0)=0?

I'm not sure, there is a variable called v_of_0 that is set to the G=0  
component of the local potential, and used to offset the bands. I think  
this is an equivalent approach, but I don't know the details.

> I am trying to find some answer by reading the source code, but any help
> will be greatly appreciated.

you're welcome

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Lorenzo Paulatto
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