QE-05

下面以Si为例，DFPT计算Gamma点声子谱。

STEP 1

依旧是pw.x进行自洽

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&control
    calculation = 'scf'
    restart_mode='from_scratch'
    prefix = 'si'
    outdir = './outdir'
    pseudo_dir = '/BIGDATA1/ac_iphy_jrsun_1/soft/QE/SSSP'
/
&system
    ibrav=2, celldm(1) =10.410909236, 
    nat=2, ntyp=1,
    ecutwfc=50
/
&electrons
    conv_thr=1e-10
/
ATOMIC_SPECIES
 Si  28.0855  Si.pbe-n-rrkjus_psl.1.0.0.UPF

ATOMIC_POSITIONS (alat)
 Si 0.00 0.00 0.00
 Si 0.25 0.25 0.25
K_POINTS (automatic)
  6 6 6 1 1 1

STEP 2

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phonon calculation at Gamma point.
&inputph
  outdir = './outdir'
  prefix = 'si',
  tr2_ph = 1.0d-14
  epsil = .true. !仅Gamma点时ture，用于计算介电常数
  amass(1) = 28.0855
  fildyn = 'si.dyn'
/
0 0 0

Use ph.x to calculate.

TH-2的6.7有bug，换成6.5计算(STEP1就用6.5重新计算)
qe.sh如下

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#!/bin/bash
export PATH=/BIGDATA1/app/Quantum_Espresso/6.5-icc-18/bin/:$PATH
yhrun -N $SLURM_NNODES -n $SLURM_NTASKS $1 < si.2_ph.in >& si.2_ph.out

output: 

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Dielectric constant in cartesian axis 

(      13.220442521      -0.000000000      -0.000000000 )
(      -0.000000000      13.220442521      -0.000000000 )
(      -0.000000000      -0.000000000      13.220442521 )
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freq (    1) =      -0.574103 [THz] =     -19.150028 [cm-1]
freq (    2) =      -0.574103 [THz] =     -19.150028 [cm-1]
freq (    3) =      -0.574103 [THz] =     -19.150028 [cm-1]
freq (    4) =      14.762433 [THz] =     492.421761 [cm-1]
freq (    5) =      14.762433 [THz] =     492.421761 [cm-1]
freq (    6) =      14.762433 [THz] =     492.421761 [cm-1]

Then the dielectric constant is 13.220442521 (11.7 in ref), the first order Raman peak ($cm^{-1}$) is 492.421761 (520 in ref)

From symmetry analysis, there are six modes around $\Gamma$ point (including two TA, one LA, two TO, one LO).

The first order Raman peak is the optical mode at $\Gamma$ point. (inelastic process involving emission of phonon or absorption of phonon), which is k-negligible.

Physics QE

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