[Pw_forum] Zone centre phonons in ZrO2 ?

[sonu kumar]

Dear all Quantum Espresso users and developers,

I am not able to reproduce the zone cente phonons in ZrO2 calculated
in PRL 78, 21, 1997.

My results, without LO-TO splitting(can be calculated, once accoustical
mode=0 cm-1 ) are:

T1u: 14.27 cm-1 <---------not zero
T1u: 219.6 cm-1
T2g: 550.35cm-1

 I am not able to make the accoustical mode=0 cm-1.
 Although  the born charges and dielectric constants are
 ok with relative error~1%.


Input files:-----------------------------------------------

scf file:
&control
    calculation='scf',             ! relax,self consistent calc.
    verbosity='high',
    restart_mode='from_scratch',   ! 'from_scratch',
    prefix='ZrO2',
    wf_collect=.true.,                    ! collect wave func in ./ZrO2.save
    tstress=.true.,
    tprnfor=.true.,
    nstep=100,                             ! default=50
    dt=20,                                      !10,      ! default=20
    etot_conv_thr=1.0D-5,          ! default=1.0D-4
    forc_conv_thr=1.0D-5,          !1.0D-4,  default=1.0D-3
    pseudo_dir = './',
    outdir='./',
 /

 &system
    ibrav = 2,
    celldm(1)=9.67
    nat=3, ntyp=2,
    ! nbnd=                              ! can calculate itself
    ecutwfc=30,                      !50,    !in Ry, no default,
initially=60
    ecutrho=350,                    !350 !300, ! 8*50=400
    !    nr1=14,
    !    nr2=14,
    !    nr3=14,
    !    nr1s=14,
    !    nr2s=14,
    !    nr3s=14,
    !    nosym=.true.,
    nspin=1,                           ! 1,2,4, "noncolin=.true."
    !    input_dft=                    ! read from PP files.
 /

 &electrons
    mixing_beta = 0.2,              ! 0.7
    conv_thr = 1.0d-12,            ! default=1.0d-06, ! 1.0d-12,1.0d-8
    diagonalization=cg              ! 'cg',!'cg', 'david', !

 /

ATOMIC_SPECIES
 Zr   0.0000 Zr.pbe-nsp-van.UPF
 O    0.0000 O.pbe-van_ak.UPF

ATOMIC_POSITIONS (crystal)
Zr 0.0  0.0  0.0
O  0.25 0.25 0.25
O  0.75 0.75 0.75

K_POINTS (automatic)
3 3 3 0 0 0                             !8 8 8 0 0
0

ph file:----------------------------
 &inputph
  tr2_ph=1.0d-14,             !1.0d-14,     ! threshold for self
consistency=1.0d-12(default)
  alpha_mix(1)=0.2,         ! default=0.7
  prefix='ZrO2',
  iverbosity=1,
  epsil=.true.,
  trans=.true.,                   ! default=true ,
  asr=.true.,
  zue=.true.,                     ! eff charges
  amass(1)=91.22400,
  amass(2)=15.99940,
  outdir='./',
  fildyn='ZrO2.dynG',       ! file where the dyn matrix is written

 /
0.0 0.0 0.0

Effect of  convergences (plane waves, k point sampling, augmentation
functions)
is checked. Forces are zero  and press~1 kbar.

Bulk mod~233 GPa, expt~267Gpa => error~13 %.

Also,in above paper LDA pp was used, but i used USPP.

So in nutshell:---
        i think USPP has to be modified or norm conserving pp should be
used.

I need your comments over this.

Thanks!!

With Regards,
Sonu Kumar

Phd Student
Physics Department
Indian Institute of Technology
Delhi-110016, India
web:-http://www.iitd.ac.in/
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