[QE-users] ESM and FCP calculation clarification

[Lucian D. Filip]

Hello all,


I am trying to understand the ESM example in the QE github repo. It says 
in the description that the example is divided in three parts but it 
doesn't mention it the parts depend on oneanother. Is this the case? 
I.e. if you don't do the first part of the example then the rest cannot 
be done?

Another point of confusion if the FCP part of the calculation. Is this a 
'relax' type of calculation or can it be performed on a regular 'scf' run?

Also this requirement of a slab to be centered in z=0. It would have 
been very informative if the example didn't use a 1 atom thin layer of 
Al for the slab. What is the vacuum region requirement for such a 
calculation?

I am trying to study a large 1x1xN structure consisting of 
SrRuO3/PbTiO3/SrTiO3/PbTiO3/SrRuO3 layers of different thicknesses. I 
would like to consider the 'bc1' case where the structure is surrounded 
by semi infinite metal electrodes. Do I still need a vaccum region for 
this case? Or I just construct a 1x1xN supercell centered around z=0 and 
se the esm_w parameter to 0.

Since my structure involves PbTiO3 which is a ferroelectric with a large 
bulk polarization, can I use FCP to obtain a correct Hartree potential 
for this case?

A simple 'scf' calculation on this 1x1xN structure surrounded by vacuum 
regions, does not converge even after hundreds of steps and no 
combination of cutoff, k points, mixing beta etc solves this problem. I 
suspect the problem lies with the effect of polarization and a possible 
solution would be ESM method (although I expect will take quite a long 
time).


Regards,


Lucian


P.S.: since the structure is quite large I am not including here an 
input file but I can provide it upon request.


---

*Dr. Lucian Dragos Filip*
National Institute of Materials Physics
Atomistilor str. 405A, PO Box MG. 7
Magurele, 077125
Bucharest, Romania
E-mail: lucian.filip at infim.ro
Website: https://lucianfilip.wordpress.com/
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