[QE-users] Does order of atoms matter in Quantum Espresso?

[Andrea Ferretti]

Dear Sheikh Ziauddin Ahmed,

the reordering of the atoms should not have an effect (besides the fact 
ths you are also swapping the coordinates of the two atoms).
The biggest difference I see here is related to the smearing, which is 
commented in the second input.

>     !occupations='smearing',
>     !smearing='gauss',
>     !degauss=0.05,

Is this wanted ?
(BTW: gaussian smearing of 0.05 Ry seems quite large to me)

take care
Andrea

> I am trying to calculate the phonon dispersion of AlSb. I am getting two different results depending on how I am introducing the atoms in the
> SCF calculation. Will the order of the atom change the symmetry of the zinc blende AlSb?
> In the first case the input deck is: 
> &system
>     ibrav=2, nat=2, ntyp=2,
>     ecutwfc = 50, ecutrho = 500,
>     occupations='smearing',
>     smearing='gauss',
>     degauss=0.05,
>     celldm(1)=11.5944146,
>  /
>  &electrons
>     conv_thr    = 1.0e-12
>     mixing_beta = 0.7
>     mixing_mode = 'local-TF'
>  /
> ATOMIC_SPECIES
>  Al 26.98 al_lda_v1.uspp.F.UPF
>  Sb 121.76 sb_lda_v1.4.uspp.F.UPF
> ATOMIC_POSITIONS (alat)
>  Al 0.0   0.0   0.0
>  Sb 0.25  0.25  0.25
> K_POINTS automatic
> 6 6 6 0 0 0
> 
> In the second case the input deck is: 
>  &system
>     ibrav=2, nat=2, ntyp=2,
>     ecutwfc = 50, ecutrho = 500,
>     !occupations='smearing',
>     !smearing='gauss',
>     !degauss=0.05,
>     celldm(1)=11.5944146,
>  /
>  &electrons
>     conv_thr    = 1.0e-12
>     mixing_beta = 0.7
>     mixing_mode = 'local-TF'
>  /
> ATOMIC_SPECIES
>  Sb 121.76 sb_lda_v1.4.uspp.F.UPF
>  Al 26.98 al_lda_v1.uspp.F.UPF
> ATOMIC_POSITIONS (alat)
>  Sb 0.0   0.0   0.0
>  Al 0.25  0.25  0.25
> K_POINTS automatic
> 6 6 6 0 0 0
> 
> Thanks in advance!
> --
> Sheikh Ziauddin Ahmed 
> PhD Candidate
> Charles L. Brown Department of Electrical and Computer Engineering
> University of Virginia
> Email:sza9wz at virginia.edu
> LinkedIn: https://www.linkedin.com/in/sheikh-ziauddin-ahmed
> 
>

-- 
Andrea Ferretti, PhD
S3 Center, Istituto Nanoscienze, CNR
via Campi 213/A, 41125, Modena, Italy
Tel: +39 059 2055322;  Skype: andrea_ferretti
URL: http://www.nano.cnr.it