[Pw_forum] anatase errors

[Giovanni Cantele]

Dear Safa,

the errors you get is because you input the TiO2 anatase primitive unit cell, but include also periodic replicas of some atoms, that means that as the scf cycle starts, some atoms overlap and it will never converge!

For example:
    Ti      0.000000000    0.000000000    0.000000000  
and
    Ti      3.730000000    0.000000000    0.000000000  
are obtained one from the other through a lattice translation (a,0,0) and so they cannot be included both in the ATOMIC_POSITIONS card if the A and C parameters specify the crystal primitive cell.

If you want to use the cif file with VESTA, before exporting the xyz coordinates you must be sure that only the atoms in the primitive cell are shown. However, you can also look through lot of papers published
on TiO2 anatase and related systems. If you do so, you discover that the unit cell contains two TiO units with Ti ions at 0,0,0 and (0, 1/2 , 1/4) and O ions at (0,0,u), (0,0,-u), (0,1/2 ,u+1/4 ) and (0,1/2 , 1/2-u) with u=0.208.
This coordinates are in crystal units.


Giovanni

-- 

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

> On 05 Nov 2015, at 02:43, Safa Alzaim <safa.alzaim at gmail.com> wrote:
> 
> Hello All,
>     I am new at QE, so please excuse the simplicity of my questions. I am working with bulk TiO2 anatase. I downloaded a cif, and then used Vesta to convert the data to xyz coordinates. However, I get the 31 atom unit cell instead of the primitive cell. In any case, I entered A and C values. I keep getting errors when I try to run the file. If anybody could help, I'd really appreciate it.
> Thanks!
> Safa
> 
> 
> &CONTROL
>                        title = anatase1 ,
>                  calculation = 'scf' ,
>                 restart_mode = 'from_scratch' ,
>                   wf_collect = .true. ,
>                       outdir = '/home/osboxes/qe/PWgui-5.2.1/' ,
>                       wfcdir = '/home/osboxes/qe/PWgui-5.2.1/' ,
>                   pseudo_dir = '/home/osboxes/qe/mypseudo/' ,
>                       prefix = 'anatasetry1' ,
>  /
>  &SYSTEM
>                        ibrav = 7,
>                            A = 3.73 ,
>                            C = 9.37 ,
>                          nat = 31,
>                         ntyp = 2,
>                      ecutwfc = 40 ,
>                      ecutrho = 320 ,
>  /
>  &ELECTRONS
>               conv_thr = 1.0d-8 ,
>                  mixing_mode = 'plain' ,
>              diagonalization = 'david' ,
>  /
> ATOMIC_SPECIES
>    Ti   46.86700  Ti.blyp-sp-hgh.UPF 
>     O   15.99400  O.blyp-hgh.UPF 
> ATOMIC_POSITIONS angstrom 
>    Ti      0.000000000    0.000000000    0.000000000    
>    Ti      0.000000000    0.000000000    9.370000000    
>    Ti      0.000000000    3.730000000    0.000000000    
>    Ti      0.000000000    3.730000000    9.370000000    
>    Ti      3.730000000    0.000000000    0.000000000    
>    Ti      3.730000000    0.000000000    9.370000000    
>    Ti      3.730000000    3.730000000    0.000000000    
>    Ti      3.730000000    3.730000000    9.370000000    
>    Ti      1.865000000    1.865000000    4.685000000    
>    Ti      0.000000000    1.865000000    2.342500000    
>    Ti      3.730000000    1.865000000    2.342500000    
>    Ti      1.865000000    0.000000000    7.027500000    
>    Ti      1.865000000    3.730000000    7.027500000    
>     O      0.000000000    0.000000000    1.874000000    
>     O      0.000000000    3.730000000    1.874000000    
>     O      3.730000000    0.000000000    1.874000000    
>     O      3.730000000    3.730000000    1.874000000    
>     O      1.865000000    1.865000000    6.559000000    
>     O      0.000000000    1.865000000    4.216500000    
>     O      3.730000000    1.865000000    4.216500000    
>     O      1.865000000    0.000000000    8.901500000    
>     O      1.865000000    3.730000000    8.901500000    
>     O      1.865000000    0.000000000    5.153500000    
>     O      1.865000000    3.730000000    5.153500000    
>     O      0.000000000    1.865000000    0.468500000    
>     O      3.730000000    1.865000000    0.468500000    
>     O      1.865000000    1.865000000    2.811000000    
>     O      0.000000000    0.000000000    7.496000000    
>     O      0.000000000    3.730000000    7.496000000    
>     O      3.730000000    0.000000000    7.496000000    
>     O      3.730000000    3.730000000    7.496000000    
> K_POINTS automatic 
>   2  2  1   1 1 1 
> 
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