<html>Dear users,<br /><br />I have a problem computing the electrons band structure of BiFeO3, antiferromagnet (no SOC), R3c space gorup,<br />with Hubbard corrections on Fe.<br />I define different starting_magnetizations for the two sublattices of spin centers, as described in the Input File Description.<br />When I compute the electronic bands I see that the degeneracy of the spin-up and spin-down states is lifted<br />only along certain directions.<br />Since the time-reversal symmetry is present but the inversion symmetry is broken I would expect the bands to respect<br />Kramers degeneracy: E_up (k) = E_dn (-k) .<br />This is not what I find, as you can see from the picture attached.<br />The energy difference can be as large as 0.2 eV, so this is not numerical noise.<br /><br />I tried different solutions, including using an explicit k-points mesh, use nosym=true, starting from different<br />initial magnetizations, but I always obtain the same odd behaviour.<br />I also tried FeO3, same procedure, with an automatically generated k-mesh, and the spin-polarized bands are degenerate as they should.<br />I paste below the input file of the self consistent calculation, I'm using version 7.0, with PAW pseudopotentials.<br /><br />I appreciate any suggestion,<br />thank you!<br /><br />Francesco Delodovici, CentraleSupelec, Universitè Paris-Saclay.<br /><br /><br />##################################################<br /><br /> &control<br /> calculation='scf'<br /> restart_mode='from_scratch',<br /> pseudo_dir = './pseudop/',<br /> outdir='./'<br /> prefix='BFO'<br /> tstress = .TRUE.<br /> tprnfor = .TRUE.<br /> /<br />&system<br /> ibrav = 0, celldm(1)=10.660942,<br /> nat= 10, ntyp=4,<br /> ecutwfc =120.0, ecutrho=600.0<br /> occupations='smearing', smearing='gaussian', degauss=0.02<br /> nspin = 2,<br /> starting_magnetization(2) = -1<br /> starting_magnetization(3) = 1<br /> lda_plus_u=.true.<br /> lda_plus_u_kind = 0<br /> Hubbard_U(2) = 4.5 <br /> Hubbard_U(3) = 4.5<br /><br /> /<br /> &electrons<br /> conv_thr = 1.0e-9<br /> /<br /><br />ATOMIC_SPECIES<br /> Bi 208.98 Bi.upf<br /> Fe1 55.85 Fe.upf<br /> Fe2 55.85 Fe.upf<br /> O 15.999 O.upf<br /><br />CELL_PARAMETERS (alat= 10.66094200)<br /> 0.496963620 -0.286922080 0.819002251<br /> -0.000000000 0.573844160 0.819002251<br /> -0.496963620 -0.286922080 0.819002251<br /><br />ATOMIC_POSITIONS (crystal)<br />Bi -0.0064211942 -0.0064211938 -0.0064211942<br />Bi 0.4935787307 0.4935787311 0.4935787307<br />Fe1 0.2189690501 0.2189690504 0.2189690501<br />Fe2 0.7189689110 0.7189689114 0.7189689110<br />O 0.3893335266 0.5347428617 0.9390758847<br />O 0.9390758845 0.3893335266 0.5347428617<br />O 0.5347428621 0.9390758842 0.3893335268<br />O 0.0347428643 0.8893334799 0.4390758846<br />O 0.8893334801 0.4390758843 0.0347428647<br />O 0.4390758848 0.0347428643 0.8893334799<br /><br />K_POINTS (automatic)<br />6 6 6 0 0 0<br /><br /> </html>