the order of the entries in the pseudopotential list or in the atomic
position list should not affect the result.
however you are not changing only the order.
1) you are also swapping the two atoms... this too should not change
anything but is not the same as changing the order only :)
2) the first calculation is metallic (with a quite large gaussian
smearing, 0.05 Ry is ~ 0.7 eV) the second uses the default insulating
setting. THIS may have a big impact, for two reasons: i) the fundamental
gap in AlSb, if I remember correctly, is not very large .. comparable to
the smearing width used; ii) being AlSb a polar material the vibrational
properties have a non analytic component ruled by the macroscopic
dielectric properties (Z*, epsilon_infty) that are disabled in the
phonon calculation of metals (where epsilon_infty diverges).
Additionally, in the phonon calculation step you should make sure you do
compute Z* and epsilon and include them in the subsequent phonon
dispersion calculation step.
HTH
stefano
On 30/12/19 23:07, Sheikh Ziauddin Ahmed wrote:
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:[email protected]_ <mailto:[email protected]>
LinkedIn: https://www.linkedin.com/in/sheikh-ziauddin-ahmed
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_______________________________________________
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