[QE-users] Difficulty with convergence using tefield

[Dr. Thomas Brumme]

Dear Alex,

if your is non-periodic in one direction (with the vacuum and the
artificial dip due to the field and dipole correction) there is no
reason to put k-points in this direction - you just increase the
computation time to get bands with no dispersion at all in this
direction. At least I think that there shouldn't be any dispersion,
otherwise something is wrong... The system is only periodic in 2D.

Anyway, another info: the main parallelization scheme in QE is
over the points in real space in z direction. So, it's always
good to have the largest unit cell dimension along z.

Cheers

Thomas


-- 
Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig

Tel:  +49 (0)341 97 36456

email: thomas.brumme at uni-leipzig.de

Zitat von "Alex.Durie" <alex.durie at open.ac.uk>:

> Dear Lorenzo,
>
>
> Thank you for your response, yes I got convergence without the field  
> in about 23 iterations, but the estimated error was much better at  
> the earlier iterations than with the field.
>
>
> I take it from your response you believe the issue lies with the  
> convergence? My k-point grid was defined so that the mesh was  
> equally spaced in reciprocal space, however I understand the system  
> is highly inhomogeneous in the field direction so I will try  
> something like 16x16x16.
>
>
> I understand what you say about edir, I believe also that the system  
> runs more efficiently with the magnetisation along the z-axis. Do  
> you think overall the code is more efficient with say edir = 3,
>
> nspin = 4, angle1(1) = 90, angle2(1) = 0? Provided that's the  
> correct way to set magnetisation along the x-axis?
>
> Many thanks,
>
> Alex
>
>
> Subject: Re: [QE-users] Difficulty with convergence using tefield
>
> Message-ID:
>         <CAG+GtJcU1YPM9MY5bsn8_p6pdg21FLrLXu9ZWN0vr==jMvho6w at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> edir=1 and 2 are extremely inefficient in parallel. Use edir=3, rotate your
> slab. Does it converge without field? Also, your choic is a of k-points
> looks the opposite of correct: you need many points along the field
> direction.
>
> --
> Lorenzo Paulatto
> Written on a virtual keyboard with real fingers
>
> On Sat, 29 Sep 2018, 20:43 Alex.Durie, <alex.durie at open.ac.uk> wrote:
>
>> Dear experts,
>>
>> I am attempting to perform an scf calculation on a semi-infinite slab of
>> ferromagnetic cobalt surrounded by a vacuum with an electric field applied
>> perpendicular to the magnetisation, out-of-plane.
>>
>> I am struggling to get convergence in the scf cycle. I achieved
>> satisfactory results using the same geometry and k-points without the field.
>>
>> I have attempted to run it with ecutwfc = 30, and ecutrho at its default
>> value. Now I am attempting ecutwfc = 46, ecutrho = 238 (as recommended in
>> the header of the pseudopotential file).
>>
>> I find in both cases the total energy and Harris-Foulkes estimate are
>> usually negative, and the estimated scf accuracy is very large, for each
>> cycle.
>>
>> The runtime for larger ecutwfc and ecutrho, is much longer.
>>
>> Is there something I'm doing wrong, or do I need to alter my expectations
>> of runtime? Please see input file below.
>>
>> I am running the code with MPI, on 4 cores. At 12 iterations, the CPU time
>> is 24737.9 secs, the total energy is -377.46347734 Ry, the Harris-Foulkes
>> estimate is -1293.19368730 Ry and the estimated scf accuracy is <
>> 3322.28583637 Ry. I have also noticed the "Adding external electric field"
>> block is duplicated on each cycle, though I suspect that's normal.
>>
>> Many thanks
>>
>> Alex Durie
>> PhD student
>> The Open University
>> United Kingdom
>>
>> &control
>>     calculation='scf'
>>     restart_mode='from_scratch',
>>     pseudo_dir = '/home/alex/QE/pslibrary.1.0.0/pz/PSEUDOPOTENTIALS/',
>>     outdir='./'
>>     prefix='co'
>>     tefield = .true.
>>     dipfield = .true.
>> /
>> &system
>>     ibrav = 8,
>>     celldm(1) =4.82388,
>>     celldm(2) =8.,
>>     celldm(3) =1.,
>>     nat= 5,
>>     ntyp= 1,
>>     ecutwfc = 46.0
>>     ecutrho = 238.0
>>     nspin = 2
>>     occupations='smearing', smearing='cold', degauss=0.02
>>     starting_magnetization = -1
>>     nbnd = 45
>>     edir = 2
>>     emaxpos = 0.41
>>     eopreg = 0.59
>>     eamp = 0.000243
>> /
>> &electrons
>>     electron_maxstep = 500
>>     diagonalization='cg'
>>     conv_thr = 1.0e-6
>>     mixing_beta = 0.3
>> /
>> ATOMIC_SPECIES
>> Co 58.933195 Co.pz-n-kjpaw_psl.1.0.0.UPF
>> ATOMIC_POSITIONS {bohr}
>> Co   0.0000000      0.0000000      0.000000
>> Co   2.4119400      3.4110000      2.411940
>> Co   0.0000000      6.8220000      0.000000
>> Co   2.4119400     10.2330000      2.411940
>> Co   0.0000000     13.6440000      0.000000
>> K_POINTS {automatic}
>> 16 2 16  0 0 0