[Pw_forum] Backward compatibility issue on elph matrix elements between QE 4.0.3 and 5.1.2
Paolo Giannozzi
p.giannozzi at gmail.com
Sat Jun 27 17:30:14 CEST 2015
You should first of all verify whether the quantity you print depends upon
the specific choice of irreps/degeneracies/phases of wavefunctions/phases
of the moon. If you are really sure that the quantity you print should not
vary across versions, a safe but slow way to figure out what happened when
and maybe why is to start from a svn version close to 4.0.3 and go up until
something happens.
Paolo
On Fri, Jun 26, 2015 at 8:23 PM, Samuel Poncé <samuel.pon at gmail.com> wrote:
> Dear developers of QE,
>
> I noticed a backward compatibility issue on the electron-phonon matrix
> element between QE 4.0.3 and 5.1.2.
>
> I was wondering if it was a bug and if not, what was the reason.
>
> I added the following line in the two versions of the code in
> PHonon/PH/elphon.f90
>
> if (ik==215) then
>
> write(*,*)'elphmat(:,:,:)**2',SUM((REAL(REAL(elphmat(:,:,:))))**2)+SUM((REAL(AIMAG(elphmat(:,:,:))))**2)
>
> This should be a physically relevant quantity that should not change
> between version (the order of the mode changed but it is not an issue).
>
> Test:
> 6x6x6 q-grid same pseudo, tol and inputs parameters
>
> There is 16 irr q-points:
>
> ( 16q-points):
> N xq(1) xq(2) xq(3)
> 1 0.000000000 0.000000000 0.000000000
> 2 -0.166666667 0.166666667 -0.166666667
> 3 -0.333333333 0.333333333 -0.333333333
> 4 0.500000000 -0.500000000 0.500000000
> 5 0.000000000 0.333333333 0.000000000
> 6 -0.166666667 0.500000000 -0.166666667
> 7 0.666666667 -0.333333333 0.666666667
> 8 0.500000000 -0.166666667 0.500000000
> 9 0.333333333 0.000000000 0.333333333
> 10 0.000000000 0.666666667 0.000000000
> 11 0.833333333 -0.166666667 0.833333333
> 12 0.666666667 -0.000000000 0.666666667
> 13 0.000000000 -1.000000000 0.000000000
> 14 0.666666667 -0.333333333 1.000000000
> 15 0.500000000 -0.166666667 0.833333333
> 16 -0.333333333 -1.000000000 0.000000000
>
> All the elphmat**2 are the same (up to 4 digits) for 13 of the 16
> q-points. For example
>
> QE 5.1.2 q = ( -0.166666667 0.166666667 -0.166666667 )
> elphmat(:,:,:)**2 0.5446267
> elphmat(:,:,:)**2 0.5446253
> elphmat(:,:,:)**2 0.9506719
> elphmat(:,:,:)**2 0.9506719
>
> freq ( 1) = 9.137536 [THz] = 304.795384 [cm-1]
> freq ( 2) = 9.137536 [THz] = 304.795384 [cm-1]
> freq ( 3) = 15.052865 [THz] = 502.109513 [cm-1]
> freq ( 4) = 39.653912 [THz] = 1322.712114 [cm-1]
> freq ( 5) = 39.653912 [THz] = 1322.712114 [cm-1]
> freq ( 6) = 40.741956 [THz] = 1359.005377 [cm-1]
>
> QE 4.0.3 q = ( -0.166666667 0.166666667 -0.166666667 )
> elphmat(:,:,:)**2 0.5446267
> elphmat(:,:,:)**2 0.9506719
> elphmat(:,:,:)**2 0.5446266
> elphmat(:,:,:)**2 0.9506719
>
> omega( 1) = 9.137611 [THz] = 304.799915 [cm-1]
> omega( 2) = 9.137611 [THz] = 304.799915 [cm-1]
> omega( 3) = 15.052641 [THz] = 502.105399 [cm-1]
> omega( 4) = 39.653770 [THz] = 1322.716173 [cm-1]
> omega( 5) = 39.653770 [THz] = 1322.716173 [cm-1]
> omega( 6) = 40.741800 [THz] = 1359.009209 [cm-1]
>
>
> But the three irr-q* 5, 10* and *16* are NOT the same:
> QE 5.1.2 q = ( 0.000000000 0.333333333 0.000000000 )
> elphmat(:,:,:)**2 0.1192376
> elphmat(:,:,:)**2 0.9861287
> elphmat(:,:,:)**2 1.348592
> elphmat(:,:,:)**2 0.3134981
>
> freq ( 1) = 11.633039 [THz] = 388.036416 [cm-1]
> freq ( 2) = 11.633039 [THz] = 388.036416 [cm-1]
> freq ( 3) = 16.188917 [THz] = 540.004156 [cm-1]
> freq ( 4) = 39.110566 [THz] = 1304.588071 [cm-1]
> freq ( 5) = 39.110566 [THz] = 1304.588071 [cm-1]
> freq ( 6) = 40.947507 [THz] = 1365.861806 [cm-1]
>
> QE 4.0.3 q = ( 0.000000000 0.333333333 0.000000000
> elphmat(:,:,:)**2 0.3075966
> elphmat(:,:,:)**2 1.354492
> elphmat(:,:,:)**2 0.1192375
> elphmat(:,:,:)**2 0.9861288
>
> omega( 1) = 11.633152 [THz] = 388.042751 [cm-1]
> omega( 2) = 11.633152 [THz] = 388.042751 [cm-1]
> omega( 3) = 16.188922 [THz] = 540.007888 [cm-1]
> omega( 4) = 39.110425 [THz] = 1304.592025 [cm-1]
> omega( 5) = 39.110425 [THz] = 1304.592025 [cm-1]
> omega( 6) = 40.947359 [THz] = 1365.865939 [cm-1]
>
> As you can see the difference for the 0,1/3,0 is not huge but significant.
> As a matter of fact when
> I'm using the dvscf produced by QE 4 or 5 for that irr-q it can lead to
> physically very different results. Therefore I would like to know which
> dvscf file is correct (QE 4 or 5)?
>
> Thank you,
>
> Best Regards,
>
> Samuel Ponce
> Department of Materials, University of Oxford
>
>
>
>
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--
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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