[QE-users] Mismatch between k-points from scf.out and q-point from system.dyn0

[Paolo Giannozzi]

On Fri, Nov 6, 2020 at 11:14 PM Ashis Kundu <ashiskundu174 at gmail.com> wrote:

Why is there a mismatch between k-points from SCF  and q-point from
> system.dyn0 (phonon calculation)?
> [...] Ideally they should be the same
>

they are the same, but the algorithms for generation and selection of the
irreducible sector are different for the two grids so the ordering and sign
may differ. Each of the points in the first set is either equal to or
equivalent to a point of the second set.

Please let me know if I am doing something wrong.
>

you aren't doing anything wrong. Or maybe you are: the scf input you sent
cannot produce the k-point grid you listed

Paolo

>
> The k-points generated from SCF
>
>     number of k points=     8  Methfessel-Paxton smearing, width (Ry)=
>  0.0200
>                        cart. coord. in units 2pi/alat
>         k(    1) = (   0.0000000   0.0000000   0.0000000), wk =   0.0740741
>         k(    2) = (  -0.3333333   0.0000000   0.0977788), wk =   0.2962963
>         k(    3) = (  -0.3333333   0.3333333   0.1955577), wk =   0.5925926
>         k(    4) = (   0.3333333   0.3333333  -0.0000000), wk =   0.2962963
>         k(    5) = (   0.0000000   0.0000000   0.1955577), wk =   0.1481481
>         k(    6) = (   0.6666667   0.0000000  -0.0000000), wk =   0.1481481
>         k(    7) = (   0.0000000  -0.3333333  -0.0977788), wk =   0.2962963
>         k(    8) = (   0.0000000   0.6666667   0.0000000), wk =   0.1481481
>
> q-point from phonon calculations (a mesh of 3x3x3 is used)
>
> 0.00000000 0.00000000 0.00000000
> -0.33333333 0.00000000 0.09777884
> 0.00000000 0.33333333 0.09777884
> -0.33333333 0.33333333 0.19555767
> 0.33333333 0.33333333 -0.00000000
> 0.00000000 0.00000000 0.19555767
> 0.66666667 0.00000000 -0.00000000
> 0.00000000 -0.66666667 -0.00000000
>
> Below are the SCF and phonon input file
>
> scf.in
> -----
> &control
>     calculation     = 'scf'
>     prefix          = 'TaP'
>     pseudo_dir      = '../pp'
>     outdir          = './'
>     wf_collect      = .true.
>     tprnfor         = .true.
>     tstress         = .true.
>  /
>  &system
>     ibrav           = 7
>     celldm(1)       = 6.173529611
>     celldm(3)       = 3.409054
>     nat             = 4
>     ntyp            = 2
>     ecutwfc         = 100
>     occupations     = 'smearing'
>     smearing        = 'mp'
>     degauss         = 0.02
>  /
>  &electrons
>     diagonalization = 'david'
>     mixing_beta     = 0.7
>     conv_thr        = 1.0d-10
>  /
> ATOMIC_SPECIES
>   Ta  180.948 Ta.pw-mt_fhi.UPF
>   P   30.974  P.pw-mt_fhi.UPF
> ATOMIC_POSITIONS {alat}
> Ta   0.0000000   0.0000000  -0.0044625
> Ta   0.0000000   0.5000000   0.8478074
> P    0.0000000   0.0000000   1.4178478
> P    0.5000000   0.0000000   0.5655748
> K_POINTS {automatic}
>  15 15 15  0 0 0
>
> ph.in
> ----
> phonon
> &inputph
>   prefix   = 'TaP'
>   fildyn   = 'TaP.dyn'
>   fildvscf = 'dvscf'
>   ldisp    = .true.
>   epsil    = .false.
>   nq1 = 3
>   nq2 = 3
>   nq3 = 3
>   tr2_ph   =  1.0d-14
>  /
>
>
> Best regards,
> Ashis
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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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