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. ################################################## &control calculation='scf' restart_mode='from_scratch', pseudo_dir = './pseudop/', outdir='./' prefix='BFO' tstress = .TRUE. tprnfor = .TRUE. / &system 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 / &electrons 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 -0.000000000 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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