[QE-users] inaccurate LDA bandstructure compared to VASP in FeSe system

[Tiangang Zhou]

Dear all,

Thanks for your quick apply and you are really helpful. I’m new to quantum
espresso and make such a mistake.

Best,
Tiangang

On March 24, 2019 at 3:57:17 PM, Ari P Seitsonen (ari.p.seitsonen at iki.fi)
wrote:


Dar Tiagang,

I guess that the value 'celldm(3)= 10.431292329' should actually be
1.46419098375312488028, as it is interpreted as c/a, not simply c. If you
use the variables 'a' and 'c' in the input they are the absolute lengths
of the cell vectors and in Ångström. Just my guess...

Greetings from Paris,

apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-

Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
Ecole Normale Supérieure (ENS), Département de Chimie, Paris
Mobile (F) : +33 789 37 24 25 (CH) : +41 79 71 90 935


On Sat, 23 Mar 2019, Tiangang Zhou wrote:

>
> Hello all,
>
> I'm working on the beta-FeSe system. In the first step I have done a
simple LDA calculation. Unfortunately, after
> adjusting ecutwfc and scf K_POINTS, I can’t get the relatively accurate
result compared to VASP and wien2k (the
> result of VASP and wien2k agree well on the fermi surface). It’s likely
that the pseudopotential has some problem
> or I miss some key steps. The input files are listed below.
>
> fe_se.scf.in
> ```
> &control
> calculation = 'scf'
> restart_mode='from_scratch',
> prefix='fe_se',
> pseudo_dir = '/home/tgzhou/softwares/qe_release_6.4/pseudo/',
> outdir='tempdir/'
> /
> &system
> ibrav=  6, celldm(1)= 7.124270293115536, celldm(3)= 10.431292329,
> nat=  4, ntyp= 2,
> ecutwfc = 120.0,
> localization_thr = 0.01,
> occupations='smearing', smearing='mp', degauss=0.02
> /
> &electrons
> mixing_beta = 0.7,
> conv_thr =  1.0d-10
> /
> ATOMIC_SPECIES
> Fe  55.845  Fe.pz-n-kjpaw_psl.1.0.0.UPF
> Se  78.96   Se.pz-n-kjpaw_psl.1.0.0.UPF
> ATOMIC_POSITIONS crystal
> Fe       0.000000000   0.000000000   0.000000000
> Fe       0.500000000   0.500000000   0.000000000
> Se       0.000000000   0.500000000   0.768115942
> Se       0.500000000   0.000000000   0.231884057
> K_POINTS automatic
> 8 8 4 0 0 0
> ```
>
> fe_se.band.in
> ```
> &control
> calculation='bands'
> pseudo_dir = '/home/tgzhou/softwares/qe_release_6.4/pseudo/',
> outdir='tempdir/',
> prefix='fe_se'
> /
> &system
> ibrav=  6, celldm(1)= 7.124270293115536, celldm(3)= 10.431292329,
> nat=  4, ntyp= 2,
> ecutwfc = 120.0,
> nbnd=20
> /
> &electrons
> /
> ATOMIC_SPECIES
> Fe  55.845  Fe.pz-n-kjpaw_psl.1.0.0.UPF
> Se  78.96   Se.pz-n-kjpaw_psl.1.0.0.UPF
> ATOMIC_POSITIONS crystal
> Fe       0.000000000   0.000000000   0.000000000
> Fe       0.500000000   0.500000000   0.000000000
> Se       0.000000000   0.500000000   0.768115942
> Se       0.500000000   0.000000000   0.231884057
> K_POINTS crystal_b
> 4
> 0.0 0.0 0.0 50
> 0.5 0.0 0.0 50
> 0.5 0.5 0.0 50
> 0.0 0.0 0.0 1
> ```
>
>
> The band structure is in the path \Gamma-X-M-\Gamma. And those two have
some similarity but the qe FeSe band are
> much more narrow.
>
> qe FeSe band structure
https://drive.google.com/file/d/1wG1Nm-f5v03-kfefJoPZ4gSD4rYaJSQa/view
> vasp FeSe band structure
https://drive.google.com/file/d/1T0iNg7oecpey2dD6BB9iNrvjS6rm7Mnr/view
>
>
> Best,
>
> Tiangang Zhou
> School of Physics
> Peking University
>
>
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