[QE-users] Difficulty with convergence using tefield

[Alex.Durie]

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<http://Co.pz>-n-kjpaw_psl.1.0.0.UPF<http://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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