[Pw_forum] STO Structure breaking - reg.,

[Paolo Giannozzi]

On Wed, 2014-03-05 at 10:04 +0530, Muthu V wrote:

> I want to study H hydrogen uptake in SrTiO3 (STO). i did preliminary
> convergence test for STO  and added atomic Hydrogen to STO Unit cell
> and then carried out variable volume relaxation.  below i attached
> Xcrysden view of input file and Output file. i do not know why the
> basic structure is breaking.

neither the lattice nor the atomic positions are very different from
the starting one, so nothing is "breaking": it is just oa problem of
visualization. Try to visualize more units (e.g. 2 in each directions)

P.
>  with this mail i have attached input file for reference.  i request
> to point wrong  usage tags or mis valued tags. any suggestion will be
> appreciated .
> 
> 
>  &CONTROL
>                        title = 'hsto' ,
>                  calculation = 'vc-relax' ,
>                 restart_mode = 'from_scratch' ,
>                   wf_collect = .false. ,
>                       outdir = '//' ,
>                   pseudo_dir = '//' ,
>                       prefix = 'hsto' ,
>                etot_conv_thr = 1.0D-7 ,
>                forc_conv_thr = 1.0D-6 ,
>                      tstress = .true. ,
>                      tprnfor = .true. ,
>  /
>  &SYSTEM
>                        ibrav = 1,
>                            A = 3.905 ,
>                            B = 3.905 ,
>                            C = 3.905 ,
>                        cosAB = 0 ,
>                        cosAC = 0 ,
>                        cosBC = 0 ,
>                          nat = 6,
>                         ntyp = 4,
>                      ecutwfc = 25 ,
>                      ecutrho = 100 ,
>                        nosym = .true. ,
>             force_symmorphic = .true. ,
>                 use_all_frac = .true. ,
>                  occupations = 'smearing' ,
>                      degauss = 0.001 ,
>                     smearing = 'gaussian' ,
>             exxdiv_treatment = 'none' ,
>  /
>  &ELECTRONS
>             electron_maxstep = 700,
>                     conv_thr = 1.0D-12 ,
>                  startingpot = 'atomic' ,
>                  startingwfc = 'atomic' ,
>                  mixing_mode = 'plain' ,
>                  mixing_beta = 0.3 ,
>              diagonalization = 'david' ,
>  /
>  &IONS
>                 ion_dynamics = 'bfgs' ,
>                ion_positions = 'from_input' ,
>                  phase_space = 'full' ,
>            pot_extrapolation = 'atomic' ,
>            wfc_extrapolation = 'first_order' ,
>  /
>  &CELL
>                cell_dynamics = 'bfgs' ,
>                  cell_factor = 2 ,
>                  cell_dofree = 'all' ,
>  /
> ATOMIC_SPECIES
>    Sr   87.62000  Sr.pw-mt_fhi.UPF 
>    Ti   47.88000  Ti.pw-mt_fhi.UPF 
>     O   16.00000  O.pw-mt_fhi.UPF 
>     H    1.00800  H.pz-mt_fhi.UPF 
> ATOMIC_POSITIONS crystal 
>    Sr      0.000000000    0.000000000    0.000000000    1  1  1 
>    Ti      0.500000000    0.500000000    0.500000000    1  1  1 
>     O      0.000000000    0.500000000    0.500000000    1  1  1 
>     O      0.500000000    0.000000000    0.500000000    1  1  1 
>     O      0.500000000    0.500000000    0.000000000    1  1  1 
>     H      0.180861000    0.180861000    0.500000000    1  1  1 
> K_POINTS automatic 
>   2 2 2   0 0 0 
> 
> 
> and final step of output file
> .........
>  End of BFGS Geometry Optimization
> Begin final coordinates
>      new unit-cell volume =    256.15080 a.u.^3 (    37.95763 Ang^3 )
> 
> CELL_PARAMETERS (alat=  7.37938055)
>    0.870870969   0.012033131   0.000000822
>    0.012033035   0.870875788   0.000000824
>    0.000000373   0.000000373   0.840637748
> 
> ATOMIC_POSITIONS (crystal)
> Sr      -0.023090315  -0.023090076  -0.000000036
> Ti       0.536760793   0.536756648   0.500001056
> O        0.025340380   0.502299235   0.500000334
> O        0.502299364   0.025344838   0.500000335
> O        0.445274884   0.445274408  -0.000001291
> H        0.194275894   0.194275947   0.499999602
> End final coordinates
> ....
> _________________________
> 
> Muthu.V  
> Madurai Kamaraj University
> __________________________
> 
> 
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-- 
 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222