cell opt of TiO2, give a wrong result, anyone help

[jjf_... at yahoo.com.cn]

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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