[QE-users] X-CrysDen atomic position error

[Giovanni Cantele]

You’re using ibrav=2, which corresponds to a cubic F (fcc). The atomic positions are in alat units. As such, as clearly stated by the error message,
atoms 1 and 2 are equivalent. Indeed, their positions are:
#1 --> a/2 a/2   0
#2 —>   0    0   0

Atom #1 lies at the center of a face, its position for a cubic bcc lattice is obtained by translating the lattice site at the origin (where atom #2 lies)
by a direct lattice vector. 

You must specify *ONLY* inequivalent atoms, their periodic replicas cannot be included in the list of atoms. There are many other similar
overlapping atoms, such as
Ca —> 0 0 0 with Ca —> 1 1 0 or Ca —> 0 0 1.

Actually, to be honest, you should probably remove *ALL ATOMS BUT TWO*. Indeed, as far as I remember, CaO has a cubic bcc lattice
with on Ca atom in 0 0 0 and on O atom in a/2 a/2 a/2 (but please check!).

Provided that, in my opinion, any question is welcome, my suggestion is that you try to give a solution to error messages by yourself before
asking people, because what you learn if you “try to solve” is priceless if compared to what you learn if you “ask to solve”. In this respect,
Quantum-ESPRESSO is an exceptional lab to make experience, since especially (but not only) for the easiest tasks (such as build the band structure of
simple solids) many error messages are self-explanatory and user-friendly!  ;-)

Giovanni



> On 17 Dec 2019, at 10:25, Pooja Vyas <poojavyas1251995 at gmail.com> wrote:
> 
> Following is my input file. I obtained the atomic position using X-CrysDen. But when I run the file it shows me an error message.
> 
> Input file:
> &control
>     calculation = 'scf',
>     prefix = '9.1334'
>     tstress= .true.
>     tprnfor= .true.
>     outdir = '/home/userpooja/cao.oct/'
>     pseudo_dir = '/home/userpooja/cao.oct/pseudo/'
>  /
>  &system
>     ibrav =  2,
>     celldm(1) = 9.1334,
>     nat =  27,
>     ntyp = 2,
>     ecutwfc = 100,
> /
> &electrons
>     mixing_beta = 0.7
>  /
> 
> ATOMIC_SPECIES
> 
> Ca 40.078  Ca.pbe-nsp-van.UPF
> O 15.999 O.pbe-van_ak.UPF
> 
> ATOMIC_POSITIONS (alat)
> Ca 0.5 0.5 0.0
> Ca 0.0 0.0 0.0
> Ca 0.5 0.0 0.5
> Ca 0.0 0.5 0.5
> O  0.0 0.0 0.5
> O  0.5 0.5 0.5
> O  0.0 0.5 0.0
> O  0.5 0.0 0.0
> Ca 0.5 0.5 1.0
> Ca 0.0 0.0 1.0
> O  0.0 0.5 1.0
> O  0.5 0.0 1.0
> Ca 0.0 1.0 0.0
> Ca 0.5 1.0 0.5
> O  0.0 1.0 0.5
> O  0.5 1.0 0.0
> Ca 0.0 1.0 1.0
> O  0.5 1.0 1.0
> Ca 1.0 0.0 0.0
> Ca 1.0 0.5 0.5
> O  1.0 0.0 0.5
> O  1.0 0.5 0.0
> Ca 1.0 0.0 1.0
> O  1.0 0.5 1.0
> Ca 1.0 1.0 0.0
> O  1.0 1.0 0.5
> Ca 1.0 1.0 1.0
> K_POINTS (automatic)
>   11 11 11 1 1 1
> 
> Error: 
> 
>  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>      task #        17
>      from check_atoms : error #         1
>      atoms #   1 and #   2 differ by lattice vector (-1, 1, 0) in crystal axis
>  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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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
            gcantele at gmail.com
Phone: +39 081 676910
Skype contact: giocan74
Web page: https://sites.google.com/view/giovanni-cantele

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