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

[Varrick Suezaki]

Dear Lorenzo,
Thank you for your response!  Why should the coordinates of the two Se2
atoms sum to 1 exactly?  Does it have to do with the type of unit cell?  Is
this off of excepted experimental data?  What material do you recommend I
look at to figure out the errors in my input crystal structure?

Thank you,
Varrick Suezaki
Department of Physics and Astronomy
University of California, Riverside

On Tue, Nov 17, 2020 at 7:41 AM Lorenzo Paulatto <paulatz at gmail.com> wrote:

> 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
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.orghttps://lists.quantum-espresso.org/mailman/listinfo/users
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20201117/03ea8221/attachment.html>