Dear users,
I have a problem computing the electrons band structure of BiFeO3,
antiferromagnet (no SOC), R3c space gorup,
with Hubbard corrections on Fe.
I define different starting_magnetizations for the two sublattices of spin
centers, as described in the Input File Description.
When I compute the electronic bands I see that the degeneracy of the spin-up
and spin-down states is lifted
only along certain directions.
Since the time-reversal symmetry is present but the inversion symmetry is
broken I would expect the bands to respect
Kramers degeneracy: E_up (k) = E_dn (-k) .
This is not what I find, as you can see from the picture attached.
The energy difference can be as large as 0.2 eV, so this is not numerical noise.
I tried different solutions, including using an explicit k-points mesh, use
nosym=true, starting from different
initial magnetizations, but I always obtain the same odd behaviour.
I also tried FeO3, same procedure, with an automatically generated k-mesh, and
the spin-polarized bands are degenerate as they should.
I paste below the input file of the self consistent calculation, I'm using
version 7.0, with PAW pseudopotentials.
I appreciate any suggestion,
thank you!
Francesco Delodovici, CentraleSupelec, Universitè Paris-Saclay.
##
calculation='scf'
restart_mode='from_scratch',
pseudo_dir = './pseudop/',
outdir='./'
prefix='BFO'
tstress = .TRUE.
tprnfor = .TRUE.
/
ibrav = 0, celldm(1)=10.660942,
nat= 10, ntyp=4,
ecutwfc =120.0, ecutrho=600.0
occupations='smearing', smearing='gaussian', degauss=0.02
nspin = 2,
starting_magnetization(2) = -1
starting_magnetization(3) = 1
lda_plus_u=.true.
lda_plus_u_kind = 0
Hubbard_U(2) = 4.5
Hubbard_U(3) = 4.5
/
conv_thr = 1.0e-9
/
ATOMIC_SPECIES
Bi 208.98 Bi.upf
Fe1 55.85 Fe.upf
Fe2 55.85 Fe.upf
O 15.999 O.upf
CELL_PARAMETERS (alat= 10.66094200)
0.496963620 -0.286922080 0.819002251
-0.0 0.573844160 0.819002251
-0.496963620 -0.286922080 0.819002251
ATOMIC_POSITIONS (crystal)
Bi -0.0064211942 -0.0064211938 -0.0064211942
Bi 0.4935787307 0.4935787311 0.4935787307
Fe1 0.2189690501 0.2189690504 0.2189690501
Fe2 0.7189689110 0.7189689114 0.7189689110
O 0.3893335266 0.5347428617 0.9390758847
O 0.9390758845 0.3893335266 0.5347428617
O 0.5347428621 0.9390758842 0.3893335268
O 0.0347428643 0.8893334799 0.4390758846
O 0.8893334801 0.4390758843 0.0347428647
O 0.4390758848 0.0347428643 0.8893334799
K_POINTS (automatic)
6 6 6 0 0 0
bands.pdf
Description: Adobe PDF document
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