[Pw_forum] Spin polarized surface band

[Peng Chen]

Hello Everyone,

Bi2Se3 slab with 6 quintuple layers is calculated. It is supposed to have
spin polarized non-degenerate surface bands. However, in the calculated
results, each band is doubly degenerated including surface band, as shown
in the left panel of attached figure. And the spin components (sigma x)
have opposite sign for degenerated surface band (S1). The input is listed
below. I am not sure if I am doing the right thing. Any suggestions are
welcome!

&control
    calculation='scf'
    wf_collect=.TRUE.
    restart_mode='from_scratch',
    prefix='BiSe.6QL.pbe.spin',
    pseudo_dir = '/data/espresso-5.0/pseudo/',
    outdir='/data/scratch/'
 /
 &system
    ibrav=4, celldm(1)=7.8196867, celldm(3)=17
     nat=30, ntyp=2,
         noncolin=.TRUE, lspinorb=.TRUE.
      starting_magnetization(1)=-0.1,
 ecutwfc = 60, ecutrho = 600,nbnd=360
  occupations='smearing', smearing='mv', degauss=0.015
 /

 &electrons
    conv_thr = 1.0e-7
    mixing_mode='local-TF'
    mixing_beta = 0.7
 /

ATOMIC_SPECIES
 Bi 208.98040 Bi.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
 Se  78.96  Se.rel-pbe-n-rrkjus_psl.1.0.0.UPF

ATOMIC_POSITIONS angstrom
Se 0 0 5.899840007
......
Se 2.069 1.194537707 60.92682666
K_POINTS (automatic)
 10 10 1 0 0 0


-- 
  Best Regards.
        Peng
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