[Pw_forum] nr fixed in q_gen subroutine : give wrong total_weight

[Paolo Giannozzi]

I do not think the routine you mention should have any effect whatsover,
unless you introduce a supercell (as in old-fashioned "mass approximation").

Paolo

On Tue, Nov 15, 2016 at 1:49 PM, Antoine JAY <antoine.jay at polytechnique.edu>
wrote:

> Dear Paolo Giannozzi and community,
>
> This 4*4*4 is important because it modifies the "total_weight" variable.
>
> Example:
> I did an interpolation  of a 5^3 q-mesh to calculate the phonon DOS.
> I get the error message:
>
> frc_blk, wrong total_weight
>
> because the condition
> ABS(total_weight-nr1*nr2*nr3).GT.1.0d-8)   of matdyn.f90/subroutine
> frc_blk
> is not fulfilled.
> in frc_blk, nr1, nr2 and nr3 have been changed through read_ifc_param and
> are each 5 as asked in ph.in.
>
> But the total_weight was 124.1 and not 125.
> This is due to the fact that total_weight is calculated through variables
> that are in the subroutine q_gen which uses fixed nr:
> INTEGER, PARAMETER:: nr1=4, nr2=4, nr3=4
>
> When I change in q_gen
> INTEGER, PARAMETER:: nr1=5, nr2=5, nr3=5
>
> the total_weight changes and is exactly 125
> and the condition was fulfilled so that the phonon DOS run without any
> error.
>
> What hypothesis did you do to keep these variables fixed?
> Am I doing something wrong?
>
>
> Antoine JAY
>
>
>
>
>
>
> I think 4x4x4 is not directly related to the q-point grid, but to the
> maximum size of the supercell (if you want to build a supercell with force
> constants computed in the unit cell. It was used once upon a time in
> GaAs/AlAs heterostructure, I think)
>
>
> Paolo
>
> On Tue, Nov 15, 2016 at 9:00 AM, Antoine JAY <
> antoine.... at polytechnique.edu>
> wrote:
>
> > Dear community and developers,
> >
> > Looking at the code of qe_6.0
> >
> > I am wondering why in PHonon/PH/matdyn.f90
> > subroutine q_gen
> >
> > the values nr1, nr2 and nr4 are fixed to be 4:
> > INTEGER, PARAMETER:: nr1=4, nr2=4, nr3=4
> >
> > whereas they should be fixed as nr1=nq1, nr2=nq2, and nr3=nq3.
> > as done by the first call of read_ifc_param(nr1, nr2, nr3).
> >
> > Is there a physical meaning?
> > Is this subroutine right if someone don't whant a 4^3 q-mesh?
> >
> > Antoine Jay
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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