Dear QE users,
I'm trying to relax a rather large 2D heterostructure. Given the large
volume of the supercell, I'm forced to perform the relaxation using the
K_POINTS {gamma} card to save memory.
The relaxation is performed using the 2D cutoff of ref. PRB, 96(7),
75448 and a large vacuum in the z-direction.
Apparently, these two options seem to not work jointly. Is this a
well-known issue?
The scf accuracy oscillates wildly and the scf cycle doesn't converge. I
tested this on different 2D heterostructures and the problem persists.
I've prepared an input file (posted below), on a much smaller unit cell
that reproduces the problem.
If the option 'assume_isolated='2D'' is removed, the calculation works
fine.
On the other end, if instead the K_POINTS {gamma} option is replaced by
K_POINTS {automatic} 1 1 1 0 0 0, the calculation works fine.
&CONTROL
calculation = 'relax',
prefix = "test",
pseudo_dir = "./pseudo",
outdir = "./out",
verbosity='high',
disk_io='high',
/
&SYSTEM
ibrav = 4,
A = 3.298035242552
C = 30.0
nat = 6,
ntyp = 2,
ecutwfc = 60,
ecutrho = 480,
occupations = 'fixed'
input_dft='VDW-DF2-B86R'
assume_isolated = '2D'
/
&ELECTRONS
conv_thr = 1.D-7,
mixing_mode='local-TF',
diagonalization= 'david',
/
&IONS
ion_dynamics='bfgs',
/
ATOMIC_SPECIES
W 183.84 W.pbe-spn-kjpaw_psl.1.0.0.UPF
Se 78.96 Se.pbe-n-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS (crystal)
W 0.000000000 0.000000000 0.110023209
Se 0.333333333 0.666666666 0.166071077
Se 0.333333333 0.666666666 0.053868439
W 0.666666666 0.333333333 -0.110001069
Se 0.000000000 0.000000000 -0.053886514
Se 0.000000000 0.000000000 -0.166075142
K_POINTS {gamma}
! K_POINTS {automatic}
! 1 1 1 0 0 0
Thank you,
Mattia Angeli,
PhD student at SISSA (Trieste), Italy.
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