[Pw_forum] about phonon calculation

[premlata pandit]

Dear Pwscf users,
Here I am sending you the input file of Li2S (large band gap semi-conductor)
for scf and phonon calculations. I have some queries regarding this

1. For electronic calculation i am using 8x8x8 k-points which results in
only 60 points. Is it enough to do correct electronic calculations?
With these 60 points only, I calculated the bulk mobulus and the equilibrium
lattice constants, which matches well with the experiment and other
theoritical results.

2. For phonon calculation, I didnt get the LO-TO splitting. Can you please
tell me what more parameters i will use to get the splitting.
I set epsil .true., but it gives the error

     from phq_readin : error #         1
     no elec. field with metals

Any suggestion is highly apperciable

li2s.scf.in

&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. ,
                        dt = 80
 /
 &SYSTEM
                     ibrav = 2,
                 celldm(1) =  10.72700,
                       nat = 3,
                      ntyp = 2 ,
                   ecutwfc = 32,
                   ecutrho = 600,
                  occupations = 'smearing' ,
                    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

li2s.ph.in

phonons of Li2S
 &inputph
 ! recover =.true.,
  tr2_ph=1.0d-12,
  alpha_mix(1)=0.6,
  prefix='Li2S',
 ! fildvscf='li2sdv',
  amass(1)=32.066,
  amass(2)=6.941,
  outdir='./OUT',
  fildyn='li2s.dyn',
 ! elph=.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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