[Pw_forum] Confused about vibrational modes of isolated molecule from ph.x

[Jin Zhang]

Indeed! Thanks very much!
BTW, is there a "tr1_ph"? This name convention is really interesting:)

Best,
Jin Zhang

On 11/27/06, Xunlei Ding <ding at sissa.it> wrote:
>
> Dear Zhang,
>
> The tr2_ph is too large in you case.
> Just change the tr2_ph=1.0d-14, you will get:
>     omega( 1) =       2.198936 [THz] =      73.349094 [cm-1]
>      omega( 2) =       3.192379 [THz] =     106.487008 [cm-1]
>      omega( 3) =       3.192379 [THz] =     106.487008 [cm-1]
>      omega( 4) =       4.915826 [THz] =     163.975388 [cm-1]
>      omega( 5) =       4.915826 [THz] =     163.975388 [cm-1]
>      omega( 6) =     131.771213 [THz] =    4395.443762 [cm-1]
>
> Yours,
> Ding
>
> Jin Zhang wrote:
>
> > Hi all,
> >
> >    I posted this issue one week ago. Now I have relaxed the structure
> > and got total force less than 5.0D-5. I used a large cubic supercell
> > with 30bohr alat and ecutwfc up to 50Ry. However, things only went
> > worse. The highest frequency from ph.x dropped from 3187 cm^(-1) to
> > 1849, while gaussian03 shows it should be around 3300cm^(-1).
> >
> > I also checked H2 molecule. In this case, I got three negative values
> > and three positive ones( values are 898,898,3679cm^-1 ). But there
> > should be only ONE vibrational frequency which corresponds to the
> > stretching mode along bonding direction. And the highest freq. is also
> > too low (should be around 43xx).
> >
> > I really couldn't figure out what's wrong. Can someone help me? Thanks
> > in advance!
> >
> > The input files for H2 are:
> > ---------------------------scf_input-----------------(run two times
> > just like example07 )-----
> >  &control
> >     calculation='scf'
> >     restart_mode='from_scratch',
> >     prefix='h2',
> >     pseudo_dir = '$PSEUDO_DIR/',
> >     outdir='$TMP_DIR/'
> >  /
> >  &system
> >     ibrav=  8, celldm(1) =18, celldm(2)= 1.0, celldm(3)=1.0,
> >     nat= 2, ntyp= 1,
> >     ecutwfc = 50.0,
> >     occupations='smearing', smearing='gausssian', degauss=0.01,
> >     la2F = .false., nspin=1,
> >  /
> >  &electrons
> >     conv_thr =  1.0d-8
> >     mixing_beta = 0.7
> >  /
> > ATOMIC_SPECIES
> >   H     1.008    H.blyp-vbc.UPF
> > ATOMIC_POSITIONS (bohr)
> > H        0.000000000   0.000000000  -0.707244771
> > H        0.000000000   0.000000000   0.707244771
> > K_POINTS {automatic}
> > 1 1 1 0 0 0
> > ------------------------------ph_input---------------------------
> >  &inputph
> >   tr2_ph=1.0d-8,
> >   prefix='h2',
> >   fildvscf='h2dv',
> >   amass(1)=1.008,
> >   outdir='$TMP_DIR/',
> >   fildyn=' h2.dyn',
> >   elph=.false.,
> >   trans=.true.,
> >   ldisp=.true.,
> >   nq1=1, nq2=1, nq3=1
> > --------------------------------------------------------------------
> >
> > Regards,
> > Jin Zhang
> >
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-- 
Dep. of Physics, Peking University
Beijing, P.R.China
Phone: 86-10-6275-3190
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