[Pw_forum] PW.x homogeneous electric field berry phase calculation in trigonal cell

[Louis Fry-Bouriaux]

Hi Lorenzo,


    I have got it to work using both automatic and manual k-points, the mistake was to specify both 'berry=.true' and 'lelfield=.true.' at the same time and using 'nscf' calculation. The process I was going by was the description in the header of bp_c_phase.f90, when as you alluded to the electric field code is very similar but separate so the latter was the correct way to go with 'scf' calculation.


For 'berry=.true.', one needs to run a normal 'scf' with 'lelfield=.false.' to get the ground state first, then the polarisation can be calculated (P=0 which is a good sign for my system) as described in bp_c_phase.f90. I will now test other gdir than 3.


For 'lelfield=.true.', one can just specify a value of the field, both auto and manual work (again with gdir=3 so far). Afterwards one can apparently do a 'nscf' run with 'berry=.true.' (and 'lelfield=.false.') which reports the polarisation in the same format as the 0 field calculation above which is now non-zero as expected.


Example 10 was helpful too, if anyone reads this that should be a good point of reference.


Finally when you were talking about the bottleneck, I suppose you were talking about the efield code, my impression so far is this is not a problem using 4 processors, I will also test using 8 and compare the time taken. I have no idea how fast it 'should' be with proper parallisation, assuming it is possible to parallelise.


Kindest regards,

Louis

________________________________
From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf of Louis Fry-Bouriaux <ellf at leeds.ac.uk>
Sent: 09 February 2017 11:38:01
To: PWSCF Forum
Subject: Re: [Pw_forum] PW.x homogeneous electric field berry phase calculation in trigonal cell


Hi Lorenzo,


   Thanks for clarifying!


   Yes that was quite silly of me to have nosym=.false., but yes it has no effect I still get the 'wrong g' error.


   I will now manually specify the k-points and relay what happens later..


   I am very interested in solving the bottleneck issue as I wish to perform a much more intensive calculation using a large amorphous cell, and later move on to using ESM, so I am debugging as best as I can to first understand the code and what exactly causes the bottleneck. Are you able to share any additional technical information on this issue?


Thank you so much for you help and assistance,

Louis

________________________________
From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf of Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.fr>
Sent: 08 February 2017 19:57:19
To: PWSCF Forum
Subject: Re: [Pw_forum] PW.x homogeneous electric field berry phase calculation in trigonal cell

On Wednesday, February 8, 2017 5:46:25 PM CET Louis Fry-Bouriaux wrote:
>     In your last email you mentioned the field 'pdir', I have not been able
> to find this in the documentation, is this what you meant?

It is the internal name of a variable in the subroutine that computes the
macroscopic polarisation, but I think it is always gdir in the end.

> as this is where the error is when I use other than gdir=3 (I added ln 364
> to identify what fails exactly)

I never did this myself, but from the code expects strings of k-points, one
after each other. Each string is formed by nppstr k-points, aligned in the
direction gdir; there can be as many string as you want, in principle to form
a grid in the two directions orthogonal to gdir.

Maybe in the case gdir=3 these string are formed "spontaneously" when using k-
points automatic, but it does not work in the other cases. The polarisation
(berry=.true.) and the electric field (lefield=.true.) codes are very similar,
but not identical, in theory the second is more general, I'm not too familiar
with either.

I've noticed that you set nosym=.false., I'm quite sure that that swith is
overridden with lefield, but to be sure, could you try to sisable it?




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