[CP2K:4105] cell opt of TiO2, give a wrong result, anyone help

[Sandeep Kumar Reddy]

Hi,
    Few comments that might help you in getting right structure.

1. Your cell parameters are very small. You need to take bigger cell and
repeat the calculations.

take at least  2 x 2 x 3  cell. (or better choice is 3 x 3 x 4)

2. Your cutoff value is less. Try increase to 280 Ry or above. or If you
are not sure about cut off value, pl. do set of single point calculations
by varying density cutoff. Check for energy convergence.


Wishes,
Sandeep


On Sun, Oct 21, 2012 at 9:52 AM, jjf_... at yahoo.com.cn <
jjf_... at yahoo.com.cn> wrote:

> Hi, energyone
>
> I want use cp2k to optimzie the cell of TiO2, The following is the input
> file:
>
> &FORCE_EVAL
>  STRESS_TENSOR ANALYTICAL
>  METHOD Quickstep
>  &DFT
>    BASIS_SET_FILE_NAME /scratch/cp2k/BASIS_MOLOPT
>    POTENTIAL_FILE_NAME /scratch/cp2k/GTH_POTENTIALS
>    &MGRID
>      CUTOFF 200
>    &END MGRID
>    &QS
>      METHOD GPW
>    &END QS
>    &SCF
>      EPS_SCF 5.E-7
>      MAX_SCF 500
>      &OT
>        MINIMIZER CG
>      &END
>    &END SCF
>    &XC
>      &XC_FUNCTIONAL PBE
>      &END XC_FUNCTIONAL
>    &END XC
>  &END DFT
>  &SUBSYS
>    &CELL
>         ABC  4.594 4.594 2.959
>         PERIODIC XYZ
>    &END CELL
>   &TOPOLOGY
>    &END TOPOLOGY
>  &COORD
> Ti   -0.0000   -0.0000    0.0000
> Ti    2.2970    2.2970    1.4795
> O     1.4003    1.4003    0.0000
> O     3.1937    3.1937    0.0000
> O     0.8967    3.6973    1.4795
> O     3.6973    0.8967    1.4795
>    &END COORD
>     &KIND TI
>     BASIS_SET DZVP-MOLOPT-SR-GTH
>     POTENTIAL GTH-PBE-q12
>    &END KIND
>    &KIND O
>     BASIS_SET DZVP-MOLOPT-SR-GTH
>     POTENTIAL GTH-PBE-q6
>    &END KIND
>  &END SUBSYS
> &END FORCE_EVAL
>  &MOTION
>  &CELL_OPT
>    KEEP_ANGLES .TRUE.
>    OPTIMIZER CG
>    &CG
>     &LINE_SEARCH
>      TYPE 2PNT
>     &END LINE_SEARCH
>    &END CG
>  &END CELL_OPT
>  &GEO_OPT
>    OPTIMIZER BFGS
>  &END GEO_OPT
>  &END MOTION
> &GLOBAL
>  PROJECT TiO2
>  RUN_TYPE CELL_OPT
>  PRINT_LEVEL LOW
> &END GLOBAL
>
>
> When completing, It give the cell parameters:
> 5.54 5.58 2.96
> and the Coordinate:
> Ti         0.4095385769        0.2898267710       -0.0352843895
> Ti         3.1801930298        2.1516147238        1.4539613109
>  O         1.9175831463        1.4494611116       -0.0449395166
>  O         3.4936489849        3.0632060642       -0.0346941550
>  O         0.7216799169        4.9591730884        1.4533505831
>  O         4.6832547080        0.9868972431        1.4635018888
>
> The a and b is remarkable larger than exp. value. More importantly, Some
> Ti-O bond are broken, see the fig. below:
>
> Anyone can give suggestion about how to do it?
>
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