[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
via Beirut 2-4 34014 Trieste Grignano / [+39] 040 3787 406 (tel) -528  
(fax)

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