[Pw_forum] unknown softening of phonon modes

[premlata pandit]

Dear Pwscf users,
I have done the phonon calculation of Li2S using 4x4x4 (8-q-points) using
this code. In this mail I am sending the scf file and the ph.in file and
also the PDC obtained in
0.0 0.0 0.0 to 1.0 0.0 0.0
direction, (our results and the reported previous results JPCM 3 (1991)
1055-1064)

In our calculated PDC we are getting good agreement at gamma points. But
when we draw in the whole brillouin zone we are getting an unwanted
softening of optical and also one of the acoustic mode in the midway of G-X
direction.
Can anybody comment on this.
It will be really helpful for my PhD work.
Regards
 &CONTROL
               calculation = 'scf' ,
              restart_mode = 'from_scratch' ,
                    outdir = './OUT',
             pseudo_dir = '/root/bipul/espresso-4.0.1/pseudo/Li2S',
             prefix = 'Li2S',
             etot_conv_thr = 1.0d-5 ,
             forc_conv_thr = 1.0d-4 ,
                   tstress = .true. ,
                   tprnfor = .true. ,
 /
 &SYSTEM
                     ibrav = 2,
                 celldm(1) =  10.78750,
                       nat = 3,
                      ntyp = 2 ,
                   ecutwfc = 32,
                   ecutrho = 600,
                  occupations = 'fixed' ,
                  smearing = 'methfessel-paxton',
 !                  degauss = 0.01
 /
 &ELECTRONS
               mixing_beta = 0.5 ,
            conv_thr =  1.0d-8
           diagonalization = 'david' ,
 /
 &IONS
 /
ATOMIC_SPECIES
 S   32.066  S.pw91-van_ak.UPF
 Li  6.914   Li.pw91-s-van_ak.UPF
ATOMIC_POSITIONS (crystal)
S  0.0 0.0 0.0
Li 0.25 0.25 0.25
Li 0.75 0.75 0.75
K_POINTS automatic
   8  8  8 1 1 1



phonons of Li2S
 &inputph
  recover =.true.,
  tr2_ph=1.0d-14,
  alpha_mix(1)=0.4,
  prefix='Li2S',
  amass(1)=32.066,
  amass(2)=6.941,
  outdir='./OUT',
  fildyn='li2s.dyn',
  epsil= .true.,
  trans= .true.,
! ldisp=.true.
 nq1=4, nq2=4, nq3=4
 /
~

~


-- 
Premlata Pandit
Ph.d. student,
Barkatullah university,
Bhopal 462026,
MP, India
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