[QE-users] Bi2Se3 vc-relax and band structure calculation

[Lorenzo Paulatto]

Your initial structure for the SCF calculation does not look right to 
me, one of the Se layers is almost interleaved with a Bi layer. The 
atomic positions of the bands calculation is also not perfect: the 
coordinate of the two Se2 atoms should sum to 1 exactly, while they do 
not. This breaks the crystal symmetry and, for such a small gap as 
Bi2Se3, is going to have an impact.

I have an input file for Bi2Se3, but I think it will save you a lot of 
time in the long run, if you work it out on your own once (It surely 
took me some time the first time).

cheers

On 2020-11-17 10:19, Varrick Suezaki wrote:
> Dear PW users,
> I'm trying to do a band structure calculation for bi2se3, but the 
> resulting band structure does not look like other DFT calculations as 
> it is missing the 0.3eV band gap.  I also tried uploading my input 
> file to SeeK-Path and the crystal structure looked wrong and 
> deformed.  Below are my vc-relax and band input files, is there 
> something I'm missing? I'm using v6.5 on a CentOS 8 Vmware workstation 
> (Sorry, new to DFT calculations).
>
> &control
> calculation = 'vc-relax'
> prefix='bi2se3rel'
> restart_mode = 'from_scratch'
> outdir= '/home/name/QEoutput'
> pseudo_dir='/home/name/quantum_espresso/q-e-qe-6.5/pseudo'
> etot_conv_thr = 1e-7
> forc_conv_thr = 1e-6
> /
> &system
> ibrav = -5, celldm(1) = 18.6947, celldm(4) = 0.9135, nat = 5, ntyp = 3,
> ecutwfc = 40, ecutrho = 500,
> rhombohedral = .true.,
> noncolin=.true.,lspinorb=.true.,starting_magnetization=0.,
> nbnd=78,
> vdw_corr = 'grimme-d2'
> /
> &electrons
> conv_thr = 1.0e-9,
> /
> &ions
> /
> &cell
> cell_dofree='ibrav'
> /
> ATOMIC_SPECIES
>  Bi   208.98  Bi.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
>  Se1  78.96   Se.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
>  Se2  78.96   Se.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
>
> ATOMIC_POSITIONS (alat)
>  Bi     0.3973     0.3973     0.3973  0 0 0
>  Bi     0.6027     0.6027     0.6027  0 0 0
>  Se1    0.0000     0.0000     0.0000  0 0 0
>  Se2    0.2079     0.2079     0.2079  0 0 0
>  Se2    0.7821     0.7821     0.7821  0 0 0
> K_POINTS (automatic)
>   8 8 8 0 0 0
>
> &control
> calculation = 'bands'
> prefix='bi2se3rel'
> restart_mode = 'from_scratch'
> wf_collect=.true.,
> verbosity='high',
> outdir= '/home/name/QEoutput'
> pseudo_dir='/home/name/quantum_espresso/q-e-qe-6.5/pseudo'
> etot_conv_thr = 1e-5
> forc_conv_thr = 1e-4
> /
> &system
> ibrav = -5, celldm(1) = 18.6947, celldm(4) = 0.9135, nat = 5, ntyp = 3,
> ecutwfc = 40, ecutrho = 500,
> rhombohedral = .true.,
> noncolin=.true.,lspinorb=.true.,starting_magnetization=0.,
> nbnd=78,
> vdw_corr = 'grimme-d2'
> /
> &electrons
> conv_thr = 1.0e-8,
> diago_full_acc=.true.,
> /
> ATOMIC_SPECIES
>  Bi   208.98  Bi.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
>  Se1  78.96   Se.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
>  Se2  78.96   Se.rel-pbe-dn-rrkjus_psl.1.0.0.UPF
>
> ATOMIC_POSITIONS crystal
>  Bi     0.3973     0.3973     0.3973  0 0 0
>  Bi     0.6027     0.6027     0.6027  0 0 0
>  Se1    1.0000     1.0000     1.0000  0 0 0
>  Se2    0.2079     0.2079     0.2079  0 0 0
>  Se2    0.7821     0.7821     0.7821  0 0 0
> K_POINTS crystal_b
> 5
>  0.00000      0.00000      0.00000     20 !gG
>  0.50000      0.50000      0.50000     20 !Z
>  0.50000      0.50000     -0.00000     20 !F
>  0.00000      0.00000      0.00000     20 !gG
>  0.00000      0.00000     -0.50000     20  !L1
>
> Thank you,
> Varrick Suezaki
> Department of Physics and Astronomy
> University of California, Riverside
>
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