[Pw_forum] negative values in the electron-phonon calculation.
Stefano Baroni
baroni at sissa.it
Thu Sep 9 16:26:14 CEST 2004
Matteo: I do not know if there is anything wrong in your data and, in
the affirmative, what may be wrong.
As a general remark, negative frequencies (better, "imaginary"
frequencies: i.e. negative squared frequencies), signal the instability
of a crystal structure towards a deformation along the phonon
distortion pattern. In principles, there is nothing wrong in this.
Whether this is due to a mistake or not, is a matter of physics ...
Hope this helps.
Stefano Baroni
On Sep 9, 2004, at 12:47 PM, matteo giantomassi wrote:
> Dear Pwscf users,
> I want to calculate the electron-phonon interaction in CaAlSi using
> LDA pseudopotentials.
> The structure has been optimized and all phonon frequences are positive
> but some values of lambda(q) e gamma(q) are negative!.
>
> ***********************************************************************
> ************************
> This is the test script i'm using:
> ***********************************************************************
> ************************
>
> #/bin/sh
> . ../environment_variables
>
> # self-consistent calculation
>
> cat > caalsi.scf.in << EOF
> &control
> calculation='scf'
> restart_mode='from_scratch',
> tstress = .true.
> tprnfor = .true.
> prefix='caalsi',
> pseudo_dir = '$PSEUDO_DIR/',
> outdir='$TMP_DIR/'
> /
> &system
> ibrav= 4, celldm(1) =7.93912, celldm(3)=1.18356, nat= 3, ntyp= 3,
> ecutwfc =20, nbnd=12,
> occupations='smearing', degauss=0.006, smearing='gaussian',
> /
> &electrons
> conv_thr = 1.0d-8
> mixing_beta = 0.7
> /
> ATOMIC_SPECIES
> Ca 40.078 Ca.pz-n-vbc.UPF
> Al 26.98154 Al.pz-vbc.UPF
> Si 28.08550 Si.pz-vbc.UPF
>
> ATOMIC_POSITIONS crystal
> Ca 0 0 0
> Al 0.333333333 0.666666666 0.5
> Si 0.666666666 0.333333333 0.5
> K_POINTS automatic
> 12 12 12 0 0 0
> EOF
> $PW_ROOT/bin/pw.x < caalsi.scf.in > caalsi.scf.out
>
> #
> # These are k-points of a (666) uniform grid in the irreducible#
> Brillouin Zone
> qpoints="0.1666667,0.0962250,0.0000000
> 0.3333333,0.1924501,0.0000000
> 0.5000000,0.2886751,0.0000000
> 0.1666667,0.2886751,0.0000000
> 0.3333333,0.3849002,0.0000000
> 0.3333333,0.5773503,0.0000000
> 0.0000000,0.0000000,0.1408181
> 0.1666667,0.0962250,0.1408181
> 0.3333333,0.1924501,0.1408181
> 0.5000000,0.2886751,0.1408181
> 0.1666667,0.2886751,0.1408181
> 0.3333333,0.3849002,0.1408181
> 0.3333333,0.5773503,0.1408181
> 0.0000000,0.0000000,0.2816362
> 0.1666667,0.0962250,0.2816362
> 0.3333333,0.1924501,0.2816362
> 0.5000000,0.2886751,0.2816362
> 0.1666667,0.2886751,0.2816362
> 0.3333333,0.3849002,0.2816362
> 0.3333333,0.5773503,0.2816362
> 0.0000000,0.0000000,0.4224543
> 0.1666667,0.0962250,0.4224543
> 0.3333333,0.1924501,0.4224543
> 0.5000000,0.2886751,0.4224543
> 0.1666667,0.2886751,0.4224543
> 0.3333333,0.3849002,0.4224543
> 0.3333333,0.5773503,0.4224543"
> for qpoint in $qpoints ; do
> #
> # non self-consistent calculation
> #
> qx=`echo $qpoint | cut -d, -f1`
> qy=`echo $qpoint | cut -d, -f2`
> qz=`echo $qpoint | cut -d, -f3`
> cat > caalsi.nscf.in << EOF
> &control
> calculation='phonon'
> restart_mode='from_scratch',
> prefix='caalsi',
> pseudo_dir = '$PSEUDO_DIR/',
> outdir='$TMP_DIR/'
> /
> &system
> ibrav= 4, celldm(1) =7.93912, celldm(3)= 1.18356, nat= 3, ntyp=
> 3,
> ecutwfc =20, nbnd=12, occupations='smearing',
> degauss=0.006, smearing='gaussian',
> /
> &electrons
> conv_thr = 1.0d-8
> /
> &phonon
> xqq(1) = $qx, xqq(2) = $qy, xqq(3) = $qz
> /
> ATOMIC_SPECIES
> Ca 40.078 Ca.pz-n-vbc.UPF
> Al 26.98154 Al.pz-vbc.UPF
> Si 28.08550 Si.pz-vbc.UPF
> ATOMIC_POSITIONS crystal
> Ca 0 0 0
> Al 0.333333333 0.666666666 0.5
> Si 0.666666666 0.333333333 0.5
> K_POINTS automatic
> 6 6 6 0 0 0
> EOF
>
> $PW_ROOT/bin/pw.x < caalsi.nscf.in >> caalsi.nscf.out
> cat > caalsi.ph.in << EOF
> phonons of caalsi at $qpoint
> &inputph
> tr2_ph=1.0d-10,
> prefix='caalsi',
> amass(1)=40.078,
> amass(2)=26.98154,
> amass(3)=28.08550,
> outdir='$TMP_DIR/',
> fildyn='dyn.$qpoint'
> fildvscf='caalsidv'
> /
> $qpoint
> EOF
> $PW_ROOT/bin/ph.x < caalsi.ph.in >> caalsi.ph.out
>
> cat > caalsi.nscf2.in << EOF
> &control
> calculation='phonon'
> restart_mode='from_scratch',
> prefix='caalsi',
> pseudo_dir = '$PSEUDO_DIR/',
> outdir='$TMP_DIR/'
> /
> &system
> ibrav= 4, celldm(1) =7.93912, celldm(3)= 1.18356, nat= 3, ntyp=
> 3,
> ecutwfc =20, nbnd=12, occupations='smearing',
> degauss=0.006, smearing='gaussian',
> /
> &electrons
> conv_thr = 1.0d-8
> /
> &phonon
> xqq(1) = $qx, xqq(2) = $qy, xqq(3) = $qz
> /
> ATOMIC_SPECIES
> Ca 40.078 Ca.pz-n-vbc.UPF
> Al 26.98154 Al.pz-vbc.UPF
> Si 28.08550 Si.pz-vbc.UPF
> ATOMIC_POSITIONS crystal
> Ca 0 0 0
> Al 0.333333333 0.666666666 0.5
> Si 0.666666666 0.333333333 0.5
> K_POINTS automatic
> 12 12 12 0 0 0
> EOF
> $PW_ROOT/bin/pw.x < caalsi.nscf2.in >> caalsi.nscf2.out
>
> cat >caalsi.elph.in<<EOF
> caalsi el-phonon at $qpoint
> &inputph
> prefix='caalsi',
> tr2_ph=1.0d-10,
> amass(1)=40.078,
> amass(2)=26.98154,
> amass(3)=28.08550,
> outdir='$TMP_DIR/',
> filelph='elph.$qpoint'
> fildyn='dyn.$qpoint'
> fildvscf='caalsidv'
> elph=.true.,
> trans=.false.,
> /
> $qpoint
> EOF
> $PW_ROOT/bin/ph.x < caalsi.elph.in >> caalsi.elph.$qpoint.out
> done
>
> ***********************************************************************
> ************************
> This is one of the output file with negative frequences:
> ***********************************************************************
> ************************
>
> 0.00000000 0.00000000 0.14081810 10 9
> 0.236982E-06 0.236982E-06 0.329897E-06 0.704514E-06 0.185522E-05
> 0.185522E-05
> 0.382096E-05 0.150028E-04 0.150028E-04
> Gaussian Broadening: 0.010 Ry, ngauss= 1
> DOS = 6.132378 states/spin/Ry/Unit Cell at Ef= 5.209036 eV
> lambda( 1)= 0.000657 gamma= 0.009865 GHz
> lambda( 2)= 0.000657 gamma= 0.009865 GHz
> lambda( 3)= 0.043325 gamma= 0.905868 GHz
> lambda( 4)= 0.237444 gamma= 10.602345 GHz
> lambda( 5)= 0.001142 gamma= 0.134227 GHz
> lambda( 6)= 0.001142 gamma= 0.134227 GHz
> lambda( 7)= 0.013474 gamma= 3.263082 GHz
> lambda( 8)= 0.000120 gamma= 0.113898 GHz
> lambda( 9)= 0.000120 gamma= 0.113898 GHz
> Gaussian Broadening: 0.020 Ry, ngauss= 1
> DOS = 6.977768 states/spin/Ry/Unit Cell at Ef= 5.211531 eV
> lambda( 1)= 0.001969 gamma= 0.033645 GHz
> lambda( 2)= 0.001969 gamma= 0.033645 GHz
> lambda( 3)= 0.151148 gamma= 3.596009 GHz
> lambda( 4)= 0.175232 gamma= 8.903105 GHz
> lambda( 5)= 0.002364 gamma= 0.316288 GHz
> lambda( 6)= 0.002364 gamma= 0.316288 GHz
> lambda( 7)= 0.028882 gamma= 7.958773 GHz
> lambda( 8)= 0.039194 gamma= 42.406162 GHz
> lambda( 9)= 0.039194 gamma= 42.406162 GHz
> Gaussian Broadening: 0.030 Ry, ngauss= 1
> DOS = 7.529356 states/spin/Ry/Unit Cell at Ef= 5.209391 eV
> lambda( 1)= 0.003371 gamma= 0.062170 GHz
> lambda( 2)= 0.003371 gamma= 0.062170 GHz
> lambda( 3)= 0.166041 gamma= 4.262610 GHz
> lambda( 4)= 0.168241 gamma= 9.223663 GHz
> lambda( 5)= 0.002268 gamma= 0.327434 GHz
> lambda( 6)= 0.002268 gamma= 0.327434 GHz
> lambda( 7)= 0.028544 gamma= 8.487177 GHz
> lambda( 8)= 0.039431 gamma= 46.034902 GHz
> lambda( 9)= 0.039431 gamma= 46.034902 GHz
> Gaussian Broadening: 0.040 Ry, ngauss= 1
> DOS = 7.670877 states/spin/Ry/Unit Cell at Ef= 5.203249 eV
> lambda( 1)= 0.001583 gamma= 0.029750 GHz
> lambda( 2)= 0.001583 gamma= 0.029750 GHz
> lambda( 3)= 0.149597 gamma= 3.912651 GHz
> lambda( 4)= 0.148433 gamma= 8.290641 GHz
> lambda( 5)= 0.001961 gamma= 0.288411 GHz
> lambda( 6)= 0.001961 gamma= 0.288411 GHz
> lambda( 7)= 0.025160 gamma= 7.621627 GHz
> lambda( 8)= 0.036271 gamma= 43.141752 GHz
> lambda( 9)= 0.036271 gamma= 43.141752 GHz
> Gaussian Broadening: 0.050 Ry, ngauss= 1
> DOS = 7.619871 states/spin/Ry/Unit Cell at Ef= 5.192300 eV
> lambda( 1)= -0.002955 gamma= -0.055152 GHz
> lambda( 2)= -0.002955 gamma= -0.055152 GHz
> lambda( 3)= 0.137191 gamma= 3.564312 GHz
> lambda( 4)= 0.157767 gamma= 8.753367 GHz
> lambda( 5)= 0.001361 gamma= 0.198827 GHz
> lambda( 6)= 0.001361 gamma= 0.198827 GHz
> lambda( 7)= 0.022826 gamma= 6.868779 GHz
> lambda( 8)= 0.034416 gamma= 40.662960 GHz
> lambda( 9)= 0.034416 gamma= 40.662960 GHz
> Gaussian Broadening: 0.060 Ry, ngauss= 1
> DOS = 7.461279 states/spin/Ry/Unit Cell at Ef= 5.177789 eV
> lambda( 1)= -0.007504 gamma= -0.137142 GHz
> lambda( 2)= -0.007504 gamma= -0.137142 GHz
> lambda( 3)= 0.127975 gamma= 3.255675 GHz
> lambda( 4)= 0.173138 gamma= 9.406301 GHz
> lambda( 5)= 0.000739 gamma= 0.105748 GHz
> lambda( 6)= 0.000739 gamma= 0.105748 GHz
> lambda( 7)= 0.021131 gamma= 6.226166 GHz
> lambda( 8)= 0.033006 gamma= 38.186120 GHz
> lambda( 9)= 0.033006 gamma= 38.186120 GHz
> Gaussian Broadening: 0.070 Ry, ngauss= 1
> DOS = 7.283095 states/spin/Ry/Unit Cell at Ef= 5.160627 eV
> lambda( 1)= -0.018199 gamma= -0.324639 GHz
> lambda( 2)= -0.018199 gamma= -0.324639 GHz
> lambda( 3)= 0.117780 gamma= 2.924747 GHz
> lambda( 4)= 0.186663 gamma= 9.898900 GHz
> lambda( 5)= -0.000793 gamma= -0.110793 GHz
> lambda( 6)= -0.000793 gamma= -0.110793 GHz
> lambda( 7)= 0.019455 gamma= 5.595627 GHz
> lambda( 8)= 0.031702 gamma= 35.801292 GHz
> lambda( 9)= 0.031702 gamma= 35.801292 GHz
> Gaussian Broadening: 0.080 Ry, ngauss= 1
> DOS = 7.134589 states/spin/Ry/Unit Cell at Ef= 5.141263 eV
> lambda( 1)= -0.038412 gamma= -0.671230 GHz
> lambda( 2)= -0.038412 gamma= -0.671230 GHz
> lambda( 3)= 0.103604 gamma= 2.520264 GHz
> lambda( 4)= 0.196871 gamma= 10.227331 GHz
> lambda( 5)= -0.003826 gamma= -0.523386 GHz
> lambda( 6)= -0.003826 gamma= -0.523386 GHz
> lambda( 7)= 0.017477 gamma= 4.924072 GHz
> lambda( 8)= 0.030406 gamma= 33.637463 GHz
> lambda( 9)= 0.030406 gamma= 33.637463 GHz
> Gaussian Broadening: 0.090 Ry, ngauss= 1
> DOS = 7.033187 states/spin/Ry/Unit Cell at Ef= 5.120081 eV
> lambda( 1)= -0.059546 gamma= -1.025752 GHz
> lambda( 2)= -0.059546 gamma= -1.025752 GHz
> lambda( 3)= 0.086926 gamma= 2.084514 GHz
> lambda( 4)= 0.203333 gamma= 10.412934 GHz
> lambda( 5)= -0.007202 gamma= -0.971260 GHz
> lambda( 6)= -0.007202 gamma= -0.971260 GHz
> lambda( 7)= 0.015317 gamma= 4.254199 GHz
> lambda( 8)= 0.029198 gamma= 31.841996 GHz
> lambda( 9)= 0.029198 gamma= 31.841996 GHz
> Gaussian Broadening: 0.100 Ry, ngauss= 1
> DOS = 6.985853 states/spin/Ry/Unit Cell at Ef= 5.097830 eV
> lambda( 1)= -0.067654 gamma= -1.157586 GHz
> lambda( 2)= -0.067654 gamma= -1.157586 GHz
> lambda( 3)= 0.071972 gamma= 1.714293 GHz
> lambda( 4)= 0.206694 gamma= 10.513791 GHz
> lambda( 5)= -0.008860 gamma= -1.186849 GHz
> lambda( 6)= -0.008860 gamma= -1.186849 GHz
> lambda( 7)= 0.013326 gamma= 3.676327 GHz
> lambda( 8)= 0.028227 gamma= 30.575707 GHz
> lambda( 9)= 0.028227 gamma= 30.575707 GHz
>
> ***********************************************************************
> ************************
> Where is the problem?. Any help would be appreciated!
>
> Thanks
>
> Matteo Giantomassi.
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---
Stefano Baroni --- SISSA & DEMOCRITOS National Simulation Center
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