[Pw_forum] Bug in ph.x sometimes occur in hexagonal phases

[Andrea Dal Corso]

Are the phonon calculated with 13 dynamical matrices wrong?
It seems a problem of fractionary translations. The point group of the
hcp is D_6h, with 24 symmetry operations but with your input pw finds 12
symmetries because the FFT mesh does not allow some symmetries.
With nr1=30, nr2=30, nr3=48 all symmetries are found correctly.

HTH,

Andrea

On Wed, 2015-08-26 at 17:36 +0300, Uri Argaman wrote:
> Dear QE users and developers
> When I do phonon calculations in hexagonal phases (titanium and zirconium)
> in a 4X4X4 q-points grid, QE calculate 12 dynamical matrices. But, in a
> specific geometries QE calculate 13 dynamical matrices, two of them are the
> same. dyn0 in that case is:
>    4   4   4
>   13
>    0.000000000000000E+00   0.000000000000000E+00   0.000000000000000E+00
>    0.000000000000000E+00   0.000000000000000E+00   0.156342786935722E+00
>    0.000000000000000E+00   0.000000000000000E+00  -0.312685573871444E+00
>    0.000000000000000E+00   0.288675134594792E+00   0.000000000000000E+00
>    0.000000000000000E+00   0.288675134594792E+00   0.156342786935722E+00
>    0.000000000000000E+00   0.288675134594792E+00  -0.312685573871444E+00
>    0.000000000000000E+00   0.288675134594792E+00  -0.156342786935722E+00
>    0.000000000000000E+00  -0.577350269189585E+00   0.000000000000000E+00
>    0.000000000000000E+00  -0.577350269189585E+00   0.156342786935722E+00
>    0.000000000000000E+00  -0.577350269189585E+00  -0.312685573871444E+00
>    0.250000000000000E+00   0.433012701892189E+00   0.000000000000000E+00
>    0.250000000000000E+00   0.433012701892189E+00   0.156342786935722E+00
>    0.250000000000000E+00   0.433012701892189E+00  -0.312685573871444E+00
> 
> You can see that the 5'th and the 7'th dynamical matrix are the same. I
> want to emphasize that this bug is only at a certain lattice parameter. For
> example, this is the input files:
> This is the SCF input:
>  &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     prefix='zr',
>     pseudo_dir = '/home/argaman/espresso_intel/pseudo/',
>     outdir='/home/argaman/tmp/tmp5110/',
>     tstress = .true. ,
>     tprnfor = .true. ,
>     verbosity='high',
>     wf_collect=.true.
>  /
>  &system
>     ibrav=  4, celldm(1) =5.98584, celldm(3) =1.59905042567 , nat= 2, ntyp=
> 1,
>     ecutwfc =45,ecutrho=225,
>     occupations='smearing', smearing="methfessel-paxton", degauss=0.01,
>  /
>  &electrons
>     conv_thr =  1.0d-9,
>     electron_maxstep=1000
>     mixing_beta = 0.7d0,
>  /
> 
> ATOMIC_SPECIES
>    Zr  91.224 zr_pbe_v1.uspp.F.UPF
> ATOMIC_POSITIONS (crystal)
>    Zr      0.666666666    0.333333333    0.250000000    0  0  0
>    Zr      0.333333333    0.666666666    0.750000000
> K_POINTS {automatic}
>  18 18 18 0 0 0
> 
> This is the phonon input:
> phonon  for Zr
>  &inputph
>   tr2_ph=1.0d-15,
>   prefix='zr',
>   fildvscf='aldv',
>   amass(1)=91.224,
>   outdir='/home/argaman/tmp/tmp5110/',
>   fildyn='zr.dyn',
>   trans=.true.,
>   ldisp=.true.,
>   nq1=4, nq2=4, nq3=4
>  /
> 
> I got this bug on versions:
> 5.0.3, 5.1 and 5.2.0
> Thank you
> Uri Argaman
> Ben-Gurion University
> Israel
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-- 
Andrea Dal Corso                    Tel. 0039-040-3787428
SISSA, Via Bonomea 265              Fax. 0039-040-3787249
I-34136 Trieste (Italy)             e-mail: dalcorso at sissa.it