[Pw_forum] error while compiling the start_q, last_q, start_irr and last_irr technique

[Andrea Dal Corso]

I am still using the start_q, last_q, start_irr and last_irr technique  
(from GRID example) to calculate the phonon dispersion in graphene.  
Everything is ok until I run ph.x for the first q (q=1 the Gamma  
point). The input is:



Phonon dispersion for monolayer graphene

  &inputph

   tr2_ph=1.0d-13,

   prefix='phmonog',

   ldisp=.true.,

   nq1=8, nq2=8, nq3=1

   start_q=1,

   last_q=1,

   start_irr=1,

   last_irr=4,

   recover=.true.,

   amass(1)=12.0107,

   outdir='/tmp/results_MOUJAES/q1',

   fildyn='mgraph881.dyn',

/

No errors in running ph.x but teh output is a bit strange like :




Program PHONON v.4.2       starts on  4Jun2010 at 14:35:33

      This program is part of the open-source Quantum ESPRESSO suite
      for quantum simulation of materials; please acknowledge
          "P. Giannozzi et al., J. Phys.:Condens. Matter 21 395502 (2009);
           URL http://www.quantum-espresso.org",
      in publications or presentations arising from this work. More details at
      http://www.quantum-espresso.org/wiki/index.php/Citing_Quantum-ESPRESSO

      Ultrasoft (Vanderbilt) Pseudopotentials
      Starting q   2 larger than total number of q points  10 or of last q   1

This error depends on the fact that the recover procedure is confused  
because the code was doing the second q point when it was interrupted  
and
now you are trying to recover (you have recover=.true.) but ask to calculate
only q point 1. You are not allowed to change start_q and last_q  
before finishing a calculation. Probably this part should be more  
robust for these kind of problems, but at the moment it is not, sorry.

When you try again and change q point to 2, the recover files are now  
a mess and you get an error from the library routine that reads
the recovering files.

At this point the only solution is to remove the outdir/_ph* files and
start again. If you have already the dynamical matrices of all q points
but the first you can simply calculate the gamma point starting from scratch.

If the problem is still present after cleaning the outdir directory,  
and it is reproducible, please post also the input of pw.x.

HTH

Andrea

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