[Pw_forum] ibrav=2 and space_group=202: input coordinate misunderstood

[Paolo Giannozzi]

If I remember correctly Wyckoff positions for fcc crystals are in simple
cubic axis (the so-called "conventional" unit cell), while the atom you are
looking at in the output is in crystal axis of the fcc cell. If you look at
the same atom in cartesian axis:
        1           Si  tau(   1) = (  -0.6943213   0.4949861   0.5050079  )
it has the same x,y,z positions as the input one, displaced by (1.5, 0.0,
0.5)

Paolo

On Fri, Sep 15, 2017 at 6:52 PM, Musil Félix <felix.musil at epfl.ch> wrote:

> Dear QE developers,
>
> I am running the following input file and the resulting output has changed
> the non equivalent scaled atomic coordinates (see highlighted in yellow). I
> compared with space group 224 with ibrav=1 and these scaled coordinates do
> match. Is there a reason for this particular behavior ?
>
> Please find attached an input file to reproduce this behavior.
>
> Cheers,
>
> Felix Musil
>
> QE INPUT:
>
> &CONTROL
>   calculation = "scf"
>   outdir = "./out/"
>   prefix = "qe"
>   pseudo_dir = "/scratch/musil/run_qe/pseudo/SSSP_acc_PBE/"
>   restart_mode = "from_scratch"
>   verbosity = "high"
>   wf_collect = .false.
> /
> &SYSTEM
>   ecutrho = 40.00000
>   ecutwfc = 10.00000
>   ibrav = 2
>   nat = 1
>   nbnd = 57
>   ntyp = 1
>   occupations = "smearing"
>   smearing = "cold"
>   degauss = 0.010000
>   space_group = 202
>   A = 11.740480817708141
> /
> &ELECTRONS
>   conv_thr = 0.10000000
> /
> ATOMIC_SPECIES
>   Si  28.0855  Si.pbe-n-rrkjus_psl.1.0.0.UPF
> ATOMIC_POSITIONS  crystal_sg
>   Si    0.80567873  0.49498614 0.00500792
>
> QE OUTPUT:
>
>      Program PWSCF v.6.1 (svn rev. 13369) starts on 15Sep2017 at 18:33: 4
>
>      This program is part of the open-source Quantum ESPRESSO suite
>      for quantum simulation of materials; please cite
>          "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/quote
>
>      Parallel version (MPI), running on     8 processors
>      R & G space division:  proc/nbgrp/npool/nimage =       8
>      Reading input from /scratch/musil/data/check_
> input_errors/sg_202-f_0-0/qe.in
> .
> .
> .
>
>      celldm(1)=  22.186293  celldm(2)=   0.000000  celldm(3)=   0.000000
>      celldm(4)=   0.000000  celldm(5)=   0.000000  celldm(6)=   0.000000
>
>      crystal axes: (cart. coord. in units of alat)
>                a(1) = (  -0.500000   0.000000   0.500000 )
>                a(2) = (   0.000000   0.500000   0.500000 )
>                a(3) = (  -0.500000   0.500000   0.000000 )
>
> .
> .
> .
>
>    Crystallographic axes
>
>      site n.     atom                  positions (cryst. coord.)
>          1           Si  tau(   1) = (  0.7043430  0.3056728  0.6842995  )
>          2           Si  tau(   2) = (  0.3056728  0.7043430  0.3056847  )
>          3           Si  tau(   3) = (  0.3056847  0.6842995  0.3056728  )
>          4           Si  tau(   4) = (  0.6842995  0.3056847  0.7043430  )
>          5           Si  tau(   5) = (  0.6842995  0.3056728  0.3056847  )
>          6           Si  tau(   6) = (  0.3056847  0.7043431  0.6842995  )
>          7           Si  tau(   7) = (  0.3056728  0.6842995  0.7043431  )
>          8           Si  tau(   8) = (  0.7043431  0.3056847  0.3056728  )
>          9           Si  tau(   9) = (  0.3056847  0.3056728  0.7043430  )
>         10           Si  tau(  10) = (  0.6842995  0.7043430  0.3056728  )
>         11           Si  tau(  11) = (  0.7043430  0.6842995  0.3056847  )
>         12           Si  tau(  12) = (  0.3056728  0.3056847  0.6842995  )
>         13           Si  tau(  13) = (  0.2956570  0.6943272  0.3157005  )
>         14           Si  tau(  14) = (  0.6943272  0.2956570  0.6943153  )
>         15           Si  tau(  15) = (  0.6943153  0.3157005  0.6943272  )
>         16           Si  tau(  16) = (  0.3157005  0.6943153  0.2956570  )
>         17           Si  tau(  17) = (  0.3157005  0.6943272  0.6943153  )
>         18           Si  tau(  18) = (  0.6943153  0.2956569  0.3157005  )
>         19           Si  tau(  19) = (  0.6943272  0.3157005  0.2956569  )
>         20           Si  tau(  20) = (  0.2956569  0.6943153  0.6943272  )
>         21           Si  tau(  21) = (  0.6943153  0.6943272  0.2956570  )
>         22           Si  tau(  22) = (  0.3157005  0.2956570  0.6943272  )
>         23           Si  tau(  23) = (  0.2956570  0.3157005  0.6943153  )
>         24           Si  tau(  24) = (  0.6943272  0.6943153  0.3157005  )
>
>
>
> Félix Musil
> Doctoral Assistant - Ph.D Student
>
> EPFL STI IMX COSMO
> LABORATORY OF COMPUTATIONAL SCIENCE AND MODELLING
> Institute of Materials Science and Engineering
> MXG 319
> Station 12
> CH-1015 Lausanne
> Switzerland
>
> E-mail: felix.musil at epfl.ch
> http://cosmo.epfl.ch/
>
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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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