[Pw_forum] QE creating wrong i/p file for crystal_sg option

[Giovanni Cantele]

If the information you have provided is correct, it seems to me that QE prints in output EXACTLY what you expect. Because you use a tetragonal lattice, the crystal units are obtained from flat units after multiplying ONLY the z
coordinate by c/a=1.55292. Therefore:
         1           Ti  tau(   1) = (   0.5000000   0.5000000   0.3219736  )   ->     0.5      0.5      0.3219736*1.55292=0.5
         2           Ti  tau(   2) = (   0.0000000   0.0000000   0.0000000  )   ->     0         0         0
         3           O   tau(   3) = (   0.0000000   0.0000000   0.4475434  )  ->     0         0         0.4475434 0.1255697=0.695 withe 0.695=1-z that is equivalent to (0,0,-z)
         4           O   tau(   4) = (   0.5000000   0.5000000   0.1255697  )  ->     0.5      0.5     0.1255697*1.55292=0.195=-z+1/2
         5           O   tau(   5) = (   0.5000000   0.5000000   0.5183776  )  ->    0.5       0.5     0.5183776*1.55292=0.805=z+1/2
         6           O   tau(   6) = (   0.0000000   0.0000000   0.1964039  )  ->    0          0        0.1964039*1.55292=z


On the right the positions are in crystal coordinates, and are EXACTLY those you have listed at the beginning of your message.

Giovanni

> On 01 Jul 2016, at 10:08, Muthu V <muthu.physicsmath at gmail.com> wrote:
> 
> Dear Users
> I have a question regarding the usage of crystal_sg option to specify atomic position in pw input file. I'm trying make pw i/p file for TiO2 rutile system. its space group # is 136 , Ti is at 2a  site and O is at 4e site.so from ITA i have the following i/p data
> 
> Ti 2a (0, 0, 0) (0.5, 0.5, 0.5)
> O  4e (0, 0, z) (0.5, 0.5, z+1/2) (0.5, 0.5, -z+1/2)(0,0,-z)
> 
> the z value is 0.305. so from this i have created following pw.x input file 
> 
> &control
>       calculation ='scf'
>      restart_mode = 'from_scratch',
>            prefix = 'ge'
>        pseudo_dir = '/home/pearl/qe-5.4.0/pseudo/',
>            outdir ='/home/pearl/qe-5.4.0/tio2/tmp/'
>  /
>  &system
>             ibrav =  6 ,
>       space_group = 136,
>                 A = 4.59373 ,
>                 C = 2.95812 ,
>               nat = 2 ,    
>              ntyp = 2 ,
>           ecutwfc = 20.0 ,
>           ecutrho = 80.0 ,
>       occupations = 'smearing' ,
>           degauss = 0.1 ,
>          smearing = 'gaussian' ,
>  /
>  &electrons
>          conv_thr =  1.0d-8 ,
>       mixing_beta = 0.7 ,
>  /
> ATOMIC_SPECIES
>  Ti  47.867   Ti.pz-mt_fhi.UPF
>  O   16.000   O.pz-mt_fhi.UPF
> ATOMIC_POSITIONS crystal_sg
> Ti   2a 
> O    4e  0.305
> K_POINTS automatic
> 4 4 4 0 0 0
> 
> with this file i'm able to run pw.x without any error message. but the following are my questions :
> 
> 1) the atomic position written in output file by pw.x is very different from the expected. why ?
> 
> from ge.pw.out file i have ( created by pw.x for above input file)
> Cartesian axes
>     site n.     atom                  positions (alat units)
>          1           Ti  tau(   1) = (   0.5000000   0.5000000   0.3219736  )
>          2           Ti  tau(   2) = (   0.0000000   0.0000000   0.0000000  )
>          3           O   tau(   3) = (   0.0000000   0.0000000   0.4475434  )
>          4           O   tau(   4) = (   0.5000000   0.5000000   0.1255697  )
>          5           O   tau(   5) = (   0.5000000   0.5000000   0.5183776  )
>          6           O   tau(   6) = (   0.0000000   0.0000000   0.1964039  )
> 
> but the atomic positions are (in crystal unit )
>  Ti    0.000000000         0.000000000         0.000000000
>  Ti    0.500000000         0.500000000         0.500000000
>   O    0.305299997         0.305299997         0.000000000
>   O    0.694700003         0.694700003         0.000000000
>   O    0.194700003         0.805299997         0.500000000
>   O    0.805299997         0.194700003         0.500000000
> 
> my second question is 
> 
> 2) why QE is not giving correct atomic position if i use crystal_sg option ?
> 
> cay anyone help me in this regard. with this mail i have enclosed the output file for the given input file
> Thank you 
> 
> ================================
> Muthu V
> Sri Paramakalyani College
> Alwarkurichi
> ================================
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

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