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

[Andrea Marini]

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.
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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