[Pw_forum] Mean internal potential for e-microscopy

[Cristian Degli Esposti Boschi]

Dear users and developers,

I have two related questions about what would be more meaningful to 
extract from a SCF calculation with DFT in Quantum Espresso as far as 
the *mean internal potential* is concerned.

This quantity, in electron microscopy experiments, is linearly related
(at least in first approx) to the response of the electron beam passing 
through a sample. In developing the theory of the response one uses the 
single particle static electic potential felt by the electrons given, in 
turn, by the solution of the Poisson equation for the total charge 
existing in the interior of the sample.

Now:

a. I wonder if the the DFT setting one has to use the Kohn-Sham 
potential (as "best" single body potential in the many-body problem)
or only the contributions coming from ions + Hartree term coming from 
the electronic charge. In a series of papers of the '90s o 2000s I have 
seen that they use the second option. The rationale would be that the 
electrons from the beam at high energy are not really a part of the 
sample and are not correlated with the ones of the interior. Would you 
agree?

b. Again in those papers they choose *linear augumented plane wave full 
potential*.
Why should one use PAW? In which sense full potentials? Aren't Pseudos 
sufficient?

Thanks a lot for your time.
-- 
Cristian Degli Esposti Boschi
CNR-IMM, Sezione di Bologna,
via Gobetti, 101, 40129, Bologna, Italia
tel. ++39 051 6399152, fax ++39 051 6399216
email: degliesposti -AT- bo.imm.cnr.it
web:   www.bo.imm.cnr.it/site/staff/personal_pages/degliesposti/