[Pw_forum] negative values in the electron-phonon calculation.
Eyvaz Isaev
eyvaz_isaev at yahoo.com
Thu Sep 9 17:03:15 CEST 2004
Hi,
In addition to Stefano's comment I can just add that
your degauss=0.005 seems to be very low.
Probably there was a mistype, because for Al (see
example 1) degauss=0.05 is used.
Best regards,
Eyvaz.
--- Stefano Baroni <baroni at sissa.it> wrote:
> 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
>
=== message truncated ===
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