[Pw_forum] Electron-Phonon: loading dVscf file when ldisp=.TRUE.

[Dal Corso Andrea]

On Mon, 2009-05-18 at 10:09 +0200, Andrea Marini wrote: 
> Dear all,
> 
>  	I am encountering a problem when calculating lambda constants 
> (PH/elephon.f90). Till now I used to
> 
> 1. calculate first phonons and  dVscf file by using
> 
>    elph=.false.,
>    trans=.true.,
>    ldisp=.false.,
> 
> in the ph.x input file.
> 
> 2. re-read the dvscf file using a larger k-point grid and changing in the 
> ph.x input file
> 
>    elph=.true.,
>    trans=.false.,
>    ldisp=.false.,
> 
> This method works great. If I compare the result of point 2 against the 
> calculation 1 using elph=.true. the lambda factors are identical.
> 
> Now I am trying to follow points 1 and 2 when ldisp=.TRUE.. Here the 
> results of the calculation 2, when the dVscf file is read from disk, are 
> different the case when phonons and lambda's are calculated in the same 
> run.

Presently the ph.x code saves on disk only the information on the actual
q point. So after a ldisp=.true. calculation you have on disk only the
dVscf of the last q point and you cannot calculate the elph for the
other q points.
I have right now committed a possible fix in the CVS version.  

HTH

Andrea




> More importantly I get that the symmetry of the  lambda factors are not 
> respected for some q-points when the dVscf file is read from disk:
> 
> < ldisp=.true., trans=.true.,  elph=.true.
> > ldisp=.true., trans=.false., elph=.true.
> 
> <      q = (    0.500000000  -0.500000000   0.500000000 )
> <
> <      omega( 1) =       3.751393 [THz] =     125.133833 [cm-1]
> <      omega( 2) =       3.751393 [THz] =     125.133833 [cm-1]
> <      omega( 3) =       9.121952 [THz] =     304.277585 [cm-1]
> <
> 
> <      lambda( 1)=  2.6170   gamma= 1077.54 GHz
> <      lambda( 2)=  2.6170   gamma= 1077.54 GHz
> <      lambda( 3)=  0.1901   gamma=  462.75 GHz
> ---
> >      lambda( 1)= 31.9820   gamma=13168.61 GHz
> >      lambda( 2)= 23.5894   gamma= 9712.95 GHz
> >      lambda( 3)= 19.7009   gamma=47963.51 GHz
> 
> 
> Maybe I am doing something wrong. I would really appreciate is someone 
> could help me.
> 
> I have attached to this mail a tar.gz file with all inputs to reproduce 
> the above described error in the simple case of Al bulk. All the runs take 
> less than 5 minutes. I have already created all the links so if you want 
> to try, simple
> 
> > cd Alluminum_TEST/
> > cd CALCULATE_DVSCF_LDISP_TRUE/
> > pw.x < gs.in > gs.out
> > ph.x < ph.in > ph.out
> > cd ../READ_DVSCF_LDISP_TRUE/
> > pw.x < gs.in > gs.out
> > ph.x < ph.in > ph.out
> > cd CALCULATE_DVSCF_SINGLE_Q/
> > pw.x < gs.in > gs.out
> > pw.x < nscf.in > nscf.out
> > ph.x < ph.in > ph.out
> > cd READ_DVSCF_SINGLE_Q
> > pw.x < gs.in > gs.out
> > pw.x < nscf.in > nscf.out
> > ph.x < ph.in > ph.out
> 
> The diff between the files CALCULATE_DVSCF_LDISP_TRUE/ph.out and 
> READ_DVSCF_LDISP_TRUE/ph.out is saved  as DIFF_LDISP_TRUE.
> 
> Cheers
> 
> Andrea
> 
> --------------------------------------------------------------------------
>                                 Andrea MARINI
> 
>         Physics Department, University of Rome "Tor Vergata" (Italy)
>                - phone: +39-0672594894 - fax: +39-062023507 -
> 
> - andrea.marini at roma2.infn.it -- http://www.yambo-code.org/people/andrea -
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-- 
Andrea Dal Corso                    Tel. 0039-040-3787428
SISSA, Via Beirut 2/4               Fax. 0039-040-3787528
34014 Trieste (Italy)               e-mail: dalcorso at sissa.it