[QE-users] Phonon dispersion of III-V superlattice

[Sheikh Ziauddin Ahmed]

Hi

I am trying to calculate the phonon dispersion of a superlattice consisting
of InAs and AlSb. However, I am ending up with negative phonon frequencies
for the structure. I used the epsil flag. But that did not help. How I can
eliminate the negative phonon modes?

For relaxation I am using the following input:
&control
    calculation='vc-relax'
    restart_mode='from_scratch',
    prefix='AlInAsSb'
    tstress = .true. ,
    tprnfor = .true. ,
    verbosity ='high'
    etot_conv_thr=1.0D-12
    forc_conv_thr=1.0D-7
 /
 &system
    ibrav=0, nat=10, ntyp=4,
    ecutwfc = 50, ecutrho = 500
 /
 &electrons
    electron_maxstep=1000
    conv_thr    = 1.0e-9
    mixing_beta = 0.7
    mixing_mode = 'local-TF'
 /
 /
&IONS
/
&CELL
 cell_dofree = 'z'
/
ATOMIC_SPECIES
 Sb 121.76   Sb.pz-n-rrkjus_psl.1.0.0.UPF
 Al 26.98  Al.pz-n-rrkjus_psl.0.1.UPF
 As 74.92      As.pz-n-rrkjus_psl.0.2.UPF
 In 114.82     In.pz-dn-rrkjus_psl.0.2.2.UPF
ATOMIC_POSITIONS {angstrom}
Sb 0.00000000  0.00000000  0.00000000
Sb 0.00000000  3.04570000  3.07106916
Sb 0.00000000  0.00000000  6.14213831
Al 1.52285000  1.52285000  1.53553458
Al -1.52285000  1.52285000  4.60660373
Al 1.52285000  1.52285000  7.67767289
As 0.00000000  3.04570000  9.21320747
As 0.00000000  0.00000000  12.24743004
In -1.52285000  1.52285000  10.73031875
In 1.52285000  1.52285000  13.76454133
K_POINTS automatic
6 6 6 0 0 0
CELL_PARAMETERS {angstrom}
3.0457000000   3.0457000000   0.0000000000
-3.0457000000   3.0457000000   0.0000000000
0.0000000000   0.0000000000   15.2816526121


For SCF run:
&control
    calculation='scf'
    restart_mode='from_scratch',
    tstress = .true. ,
    tprnfor = .true. ,
 /
 &system
    ibrav=0, nat=10, ntyp=4,
    ecutwfc = 50, ecutrho = 500
 /
 &electrons
    conv_thr    = 1.0e-9
    mixing_beta = 0.7
    mixing_mode = 'local-TF'
 /
ATOMIC_SPECIES
  Sb 121.76   Sb.pz-n-rrkjus_psl.1.0.0.UPF
 Al 26.98  Al.pz-n-rrkjus_psl.0.1.UPF
 As 74.92      As.pz-n-rrkjus_psl.0.2.UPF
 In 114.82     In.pz-dn-rrkjus_psl.0.2.2.UPF
ATOMIC_POSITIONS {angstrom}
Sb       0.000000000   0.000000000   0.280559797
Sb       0.000000000   3.045700000   3.229150822
Sb       0.000000000   0.000000000   6.101422626
Al       1.522850000   1.522850000   1.784998522
Al      -1.522850000   1.522850000   4.668823707
Al       1.522850000   1.522850000   7.525405573
As       0.000000000   3.045700000   8.683670011
As       0.000000000   0.000000000  11.527025485
In      -1.522850000   1.522850000  10.092147868
In       1.522850000   1.522850000  13.117431792
K_POINTS automatic
6 6 6 0 0 0
CELL_PARAMETERS {angstrom}
   3.045700000   3.045700000   0.000000000
  -3.045700000   3.045700000   0.000000000
   0.000000000   0.000000000  14.843532218

Regards,
Sheikh

-- 
*Sheikh Ziauddin Ahmed *
PhD Candidate
Charles L. Brown Department of Electrical and Computer Engineering
University of Virginia
Email:sza9wz*@virginia.edu* <sza9wz at virginia.edu>
LinkedIn: https://www.linkedin.com/in/sheikh-ziauddin-ahmed
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200108/532aa917/attachment.html>