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

[Ari P Seitsonen]

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
> 
> 
>