[QE-users] How can I reproduce correct phonon frequencies ?
Lorenzo Paulatto
paulatz at gmail.com
Fri Apr 26 12:02:17 CEST 2019
Hello, did you try to set a direction for the LO-TO splitting in the dynmat
input?
Kind regards
--
Lorenzo Paulatto
On Fri, 26 Apr 2019, 10:16 Atsushi Yamada, <ayamada224 at gmail.com> wrote:
> Hi,
>
> I'm beginner of QE (just I started to use it from a week ago) and I'm
> facing a problem that my calculations do not reproduce correct phonon
> frequencies. My material is 4H-SiC which is popular and well studied. I
> want to reproduce phonon frequencies at gamma point shown in Fig.2(b) of
> the following paper:
> https://arxiv.org/pdf/1705.02634.pdf
>
> It tells that the phonon dispersion in the figure is calculated by Quantum
> Espresso v 5.4.0 and calculation conditions are given. I calculated with
> the same conditions, but the high phonon frequencies region are not good
> agreement. I tried many calculations with various options and parameters,
> but I couldn't get good agreement, and now, I have no idea to solve it. My
> resultant frequencies at the gamma point are:
>
> # mode [cm-1] [THz] IR
> 1 -0.00 -0.0000 0.0000
> 2 -0.00 -0.0000 0.0000
> 3 0.00 0.0000 0.0000
> 4 192.54 5.7721 0.0000
> 5 192.54 5.7721 0.0000
> 6 200.76 6.0186 0.0000
> 7 200.76 6.0186 0.0000
> 8 259.89 7.7914 0.0015
> 9 259.89 7.7914 0.0015
> 10 404.77 12.1347 0.0000
> 11 412.80 12.3755 0.0000
> 12 613.53 18.3931 0.1675
> 13 785.34 23.5439 0.0320
> 14 785.34 23.5439 0.0320
> 15 793.13 23.7774 0.0000
> 16 793.13 23.7774 0.0000
> 17 795.96 23.8622 85.2162
> 18 801.09 24.0162 0.0000
> 19 801.09 24.0162 0.0000
> 20 811.70 24.3343 80.2329
> 21 811.70 24.3343 80.2329
> 22 851.64 25.5315 0.3206
> 23 926.17 27.7658 0.0000
> 24 935.31 28.0398 0.0000
>
> Especially, modes 20-24 are obviously different from the paper (and other
> literature): The paper is like, (probably) frequencies of the modes 22 and
> 23 are close (but my result is not like that) and modes 20 and 21 are not
> degenerated (but my result shows degeneracy). The results of my
> calculations did not change if I use other options, thresholds and
> pseudopotential.
> Maybe relating to this problem, my cell size obtained by geometry
> optimization is not the same to the values shown in the paper (3.07A,
> 10.05A in Table 1 of the paper).
>
> My input files and calculations are as followings:
> (now, I used latest version of QE, 6.4.1, but result by QE 5.4 was the
> same)
>
> (1) geometry optimization:
> pw.x -in ./SiC.opt.in > ./SiC.opt.out
> (2) SCF calculation:
> pw.x -in ./SiC.scf.in > ./SiC.scf.out
> (3) Phonon calculation
> ph.x -in ./SiC.phG.in > ./SiC.phG.out
> (4) Dynamical matrix calculation
> dynmat.x < SiC.dynmat.in > SiC.dynmat.out
>
> Input files:
> [1] SiC.opt.in
> &control
> calculation='vc-relax'
> prefix='SiC',
> pseudo_dir = './pseudo/',
> outdir='./tmp/'
> etot_conv_thr=1d-7
> forc_conv_thr=1d-7
> /
> &system
> ibrav= 4,
> A= 3.0760,
> C= 10.0400,
> nat= 8,
> ntyp= 2,
> ecutwfc = 60.0,
> ecutrho =240
> /
> &electrons
> conv_thr = 1.0d-10
> /
> &ions
> ion_dynamics='bfgs'
> /
> &cell
> cell_dofree='ibrav'
> /
> ATOMIC_SPECIES
> Si 28.086 Si.pz-n-nc.UPF
> C 12.0107 C.pz-nc.UPF
> ATOMIC_POSITIONS angstrom
> Si 0.00000000 1.77592943 2.51000000
> C 0.00000000 1.77592943 4.39250000
> Si 0.00000000 0.00000000 0.00000000
> C 0.00000000 0.00000000 1.88250000
> Si 1.53800000 0.88796471 7.53000000
> C 1.53800000 0.88796471 9.41250000
> Si 0.00000000 0.00000000 5.02000000
> C 0.00000000 0.00000000 6.90250000
> K_POINTS automatic
> 8 8 4 0 0 0
> ------------------------
>
> [2] SiC.scf.in
> &control
> calculation='scf'
> prefix='SiC',
> pseudo_dir = './pseudo/',
> outdir='./tmp/'
> /
> &system
> ibrav= 4,
> A= 3.04337366, !<-- obtained from the optimization
> C= 9.96163727, !<-- obtained from the optimization
> nat= 8,
> ntyp= 2,
> ecutwfc = 60.0,
> ecutrho =240
> /
> &electrons
> conv_thr = 1.0d-10
> /
> ATOMIC_SPECIES
> Si 28.086 Si.pz-n-nc.UPF
> C 12.0107 C.pz-nc.UPF
> ATOMIC_POSITIONS angstrom
> Si 0.000000000 1.757092472 2.489491419
> C 0.000000000 1.757092472 4.362543288
> Si 0.000000000 -0.000000000 -0.001538102
> C -0.000000000 -0.000000000 1.865935344
> Si 1.521686716 0.878546231 7.470309676
> C 1.521686716 0.878546231 9.343361545
> Si -0.000000000 0.000000000 4.979280155
> C -0.000000000 0.000000000 6.846753601
> K_POINTS automatic
> 8 8 4 0 0 0
> -------------------------
>
> [3] SiC.phG.in
> Phonons of SiC at Gamma
> &inputph
> tr2_ph=1.0d-16,
> prefix='SiC',
> outdir='./tmp'
> fildyn='SiC.dynG',
> epsil=.true.
> /
> 0.0 0.0 0.0
> -------------------------
>
> [4] SiC.dynmat.in
> &input
> fildyn='SiC.dynG',
> asr='simple'
> /
> ------------------------
>
> What is wrong...?
> I'm so glad if you kindly help me.
>
> best,
> Atsushi Yamada
>
>
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