[Pw_forum] Problem in carrying out Phonon calculations

[saswata halder]

On Wed, May 13, 2015 at 11:55 PM, saswata halder <sanky.h at gmail.com> wrote:
> Dear All,
>
> I am a beginner in quantum espresso. I am trying to perform phonon
> calculation for SrTiO3. I am able to perform the calculations but I am
> not able to reproduce the results for SrTiO3 which are already
> published in PHYSICAL REVIEW B 83, 134108 (2011).
>
> http://journals.aps.org/prb/pdf/10.1103/PhysRevB.83.134108
>
> The input file for relax is given below.
>
>  &CONTROL
>     calculation='relax',
>     restart_mode='restart',
>     prefix='ST'
>     pseudo_dir = '/home/quantum/quantum/
> potentials/',
>     outdir='./'
>     tstress=.true.
>     tprnfor=.true.
>     wf_collect=.true.
>     nstep=1000
>     etot_conv_thr=1.0D-8
>     forc_conv_thr=1.0D-6
>     disk_io='high'
>  /
>  &SYSTEM
>     ibrav = 1, celldm(1) =7.38, nat = 5, ntyp= 3,
>     ecutwfc = 40.0, ecutrho=600, occupations='fixed',
>     smearing='gaussian', degauss=0.01
>  /&ELECTRONS
>     diagonalization='cg',
>     mixing_mode='plain',
>     mixing_beta = 0.7D0
>     conv_thr =  1.0D-9
>     electron_maxstep=1000
>  /
> &ions
> /
> ATOMIC_SPECIES
>  Sr  87.620  Sr.pbe-mt_fhi.UPF
>  Ti  47.867  Ti.pbe-mt_fhi.UPF
>  O   15.999  O.pbe-mt_fhi.UPF
> ATOMIC_POSITIONS crystal
>  Sr 0.00 0.00 0.00 0 0 0
>  Ti 0.50 0.50 0.50 0 0 0
>  O  0.50 0.50 0.00 0 0 0
>  O  0.00 0.50 0.50 0 0 0
>  O  0.50 0.00 0.50 0 0 0
> K_POINTS automatic
>   6 6 6   0 0 0
>
> The input file for phonon is given below:
>
> phonons of ST at Gamma
>  &inputph
>   tr2_ph=1.0d-14,
>   prefix='ST',
>   epsil=.true.,
>   amass(1)=87.620,
>   amass(2)=47.867,
>   amass(3)=15.999,
>   outdir='./'
>   fildyn='ST.dynG',
>  /
> 0.0 0.0 0.0
> The frequencies obtained are given below:
>
>      omega(  1 -  3) =         35.5  [cm-1]   -->  T_1u G_15  G_4- I
>      omega(  4 -  6) =        151.8  [cm-1]   --> T_1u G_15  G_4- I
>      omega(  7 -  9) =        187.0  [cm-1]   --> T_1u G_15  G_4- I
>      omega( 10 - 12) =        213.6  [cm-1]   --> T_2u G_25  G_5-
>      omega( 13 - 15) =        600.7  [cm-1]   --> T_1u G_15  G_4- I
>
> I also carried out phonon calculations using the volume cell
> relaxation. the input files for both vc-relax and phonon are:
>
>  &CONTROL
>     calculation='vc-relax',
>     restart_mode='restart',
>     prefix='ST'
>     pseudo_dir = '/home/quantum/quantum/
> potentials/',
>     outdir='./'
>     tstress=.true.
>     tprnfor=.true.
>     verbosity='high'
>     wf_collect=.true.
>     nstep=1000
>     etot_conv_thr=1.0D-8
>     forc_conv_thr=1.0D-6
>     disk_io='high'
>  /
>  &SYSTEM
> ecutwfc = 40.0, ecutrho=500, occupations='fixed',
>     smearing='gaussian', degauss=0.01
>  /
>  &ELECTRONS
>     diagonalization='cg',
>     mixing_mode='plain',
>     mixing_beta = 0.7D0
>     conv_thr =  1.0D-9
>     electron_maxstep=1000
>  /
> &IONS
>     ion_dynamics='bfgs'
> /
> &CELL
>     cell_dynamics='bfgs',
>     press=2.0,
>     press_conv_thr=0.5,
> /
> ATOMIC_SPECIES
>  Sr  87.620  Sr.pbe-mt_fhi.UPF
>  Ti  47.867  Ti.pbe-mt_fhi.UPF
>  O   15.999  O.pbe-mt_fhi.UPF
> ATOMIC_POSITIONS crystal
>  Sr 0.00 0.00 0.00 0 0 0
>  Ti 0.50 0.50 0.50 0 0 0
>  O  0.50 0.50 0.00 0 0 0
>  O  0.00 0.50 0.50 0 0 0
>  O  0.50 0.00 0.50 0 0 0
> K_POINTS automatic
>   6 6 6   1 1 1
>
> phonons of ST at Gamma by anup
>  &inputph
>   tr2_ph=1.0d-14,
>   prefix='ST',
>   epsil=.true.,
>   amass(1)=87.620,
>   amass(2)=47.867,
>   amass(3)=15.999,
>   outdir='./'
>   fildyn='ST.dynG',
>  /
> 0.0 0.0 0.0
>
> the output for phonon frequencies as obtained is given below:
>
>
>      omega(  1 -  3) =       -628.3  [cm-1]   --> T_2u G_25  G_5-
>      omega(  4 -  6) =       -615.5  [cm-1]   --> T_1u G_15  G_4- I
>      omega(  7 -  9) =       -375.6  [cm-1]   --> T_1u G_15  G_4- I
>      omega( 10 - 12) =        190.2  [cm-1]   --> T_1u G_15  G_4- I
>      omega( 13 - 15) =        811.8  [cm-1]   --> T_1u G_15  G_4- I
>
> I have carried out both the relax and volume cell relaxations and have
> obtained two different results in the phonon mode calculations. Both
> the results are not matching with reported results for SrTiO3.
> Could you please suggest as to which of the methods is applicable to
> SrTiO3 system so as to provide me with more accurate results.
>
> Thanking you,
>
> With Regards.
>
> Saswata Halder.