[QE-users] What makes the "local ionic potential V_bare" local?

[Stefano Baroni]

> 
> The word "local" makes me concerned that this is a simple sum q/R of the pseudonuclei in the unit cell; in fact I would like the overall crystal potential calculated e.g. with an Ewald sum.
> 
> What does the word 'local' mean here?

The “local potential” is, uhm, the local component of the ionic pseudopotential (i.e. the sum of all those ionic pseudo potentials). “Local” in the quantum mechanical sense: the component that commutes with the position operator (i.e. it is a multiplicative operator in the coordinate representation). If yhis terminology is unfamiliar to you, I would advise you to browse some standard text in quantum mechanics (the older the better: Messiah's or Schiff's would probably do if you do not dare to open Dirac’s, which you should do once in your life), plus some early references on norm-conserving pseudo potentials, such as Hamann-Schluter-Chiang (https://doi.org/10.1103/PhysRevLett.43.1494 <https://doi.org/10.1103/PhysRevLett.43.1494> ) or Bachelet-Hamann-Schluter. In any event, the “local ionic PP has a q/r tail at large distances. At shorter distances (i.e. within the ionic core) if is usually regular down to r=0.

> Will "plot_num = 11" actually give me the crystal electrostatic potential, including the Hartree potential via FFT and ionic potential via Ewald sum?

Probably so. Easy to check by yourself in some simple case if are in doubt …

Hope this helps
Stefano B

—
Stefano Baroni -  SISSA, Trieste - http://stefano.baroni.me, stefanobaroni (skype)

There are two ways of doing a theoretical calculation: you should have either a clear physical model in mind, or a rigorous mathematical basis. You have neither. [E. Fermi to F.J. Dyson, as humbly reported by the latter]

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