Optimisation of solid state compound

[mj.be... at hotmail.co.uk]

Dear all,

I am currently studying solid state compounds using DFT methods with PBE incp2k v2.6. In particular, I am studying the compound SrO. I, however, am having trouble at the first hurdle as I am unable to optimise the structure without massive distortions taking place in the structure. I have also done this for a more simple compound such as SrO but still maintain the same problem. The resulting structure after the calculation has finished heavily distorted and is not in fact optimised. The coordinates used in the input file are those after those of when the atoms repeated by symmetry have been deleted.

Here is my input:

&FORCE_EVAL
  METHOD Quickstep
  &DFT
  BASIS_SET_FILE_NAME  ./BASIS_MOLOPT
  POTENTIAL_FILE_NAME ./GTH_POTENTIALS
    &MGRID
      CUTOFF 280
    &END MGRID
    &QS
    &END QS
    &SCF
      EPS_SCF 1.0E-7
      MAX_SCF 500
      SCF_GUESS RESTART
      &OT
       PRECONDITIONER FULL_ALL 
       MINIMIZER DIIS
      &END OT
    &END SCF
    &POISSON
    POISSON_SOLVER PERIODIC
    PERIODIC       XYZ
    &END POISSON
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
    &PRINT
     &E_DENSITY_CUBE
     &END
    &END
  &END DFT
  &SUBSYS
    &CELL
ABC  5.161500   5.161500   5.161500
    &END CELL
    &COORD
Sr    2.580750    2.580750    2.580750
Sr    2.580750    5.161500    0.000000
Sr    0.000000    2.580750    0.000000
Sr    0.000000    0.000000    2.580750
 O    0.000000    0.000000    0.000000
 O    0.000000    2.580750    2.580750
 O    2.580750    0.000000    2.580750
 O    2.580750    2.580750    0.000000
    &END COORD
    &KIND Sr
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q10 
    &END KIND
    &KIND O
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q6
    &END KIND
&TOPOLOGY
&GENERATE
BONDLENGTH_MAX 8.
&END
&END
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PROJECT SrO_GEOPT
  RUN_TYPE GEO_OPT
  PRINT_LEVEL MEDIUM
  PREFERRED_FFT_LIBRARY FFTSG
&END GLOBAL

&MOTION
  &GEO_OPT
    MAX_ITER 300
    MAX_FORCE 1.E-5
    OPTIMIZER BFGS
  &END GEO_OPT
&END MOTION
 


 Here is the coordinates for the resulting geometry of SrO:


     &CELL
       A     5.1615000000000002E+00    0.0000000000000000E+00    0.0000000000000000E+00
       B     0.0000000000000000E+00    5.1615000000000002E+00    0.0000000000000000E+00
       C     0.0000000000000000E+00    0.0000000000000000E+00    5.1615000000000002E+00
       MULTIPLE_UNIT_CELL  1 1 1
     &END CELL
     &COORD
Sr    1.9890028994522615E+00    2.2193294449078076E+00    2.7910266626701881E+00
Sr    1.9292986629548623E+00    4.8135192380570206E+00    2.1296902553214103E-01
Sr   -5.9176277362609420E-01    2.7509938085013901E+00   -3.0581129089048587E-01
Sr   -6.5144865196079582E-01    1.5680073585860360E-01    2.2722491342258304E+00
O    4.7898927316432355E-01    8.6395713176665057E-01   -1.0487832154631918E+00
O    4.7694627804364587E-01    3.4395703896268177E+00    1.6198967879945019E+00
O    3.0597429820934190E+00   -1.0551228958752437E+00    3.5339829819921467E+00
O    3.0576968263194555E+00    1.5307475361163412E+00    8.6527187533043926E-01
    &END COORD


I am really unsure what the problem is and would appreciate any help that people can give me.

Many Thanks

Matthew Bennett