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: [email protected]
Zitat von "Alex.Durie" <[email protected]>:
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
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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, <[email protected]> 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
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