convergence of the electronic wavefunction for metal surface

[ires]

Hi,

maybe someone can help me with this: I'm trying to perform a geometry
optimization of C2H2 on Cu(100), and I can't get the electronic SCF to
convergence without using OT (with OT it's no problem, but since it is
a metallic surface, I thought it's better not to use OT?)
I tried adding MOs and also smearing - here is one of the inputs I
used:

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME  /users/depart1/irespond/cp2k/BASIS_MOLOPT
    POTENTIAL_FILE_NAME /users/depart1/irespond/cp2k/GTH_POTENTIALS
#   RESTART_FILE_NAME ./cuc2h2_pbe-RESTART.wfn
    &MGRID
      CUTOFF 600
    &END MGRID
    &QS
      EPS_DEFAULT 1.0E-8
    &DISTRIBUTION
      SKIP_OPTIMIZATION TRUE
    &END DISTRIBUTION
    &END QS
    &SCF
      EPS_SCF 1.0E-7
      SCF_GUESS ATOMIC
      MAX_SCF 500
      ADDED_MOS 50
      &DIAGONALIZATION T
      &END DIAGONALIZATION
      &OUTER_SCF
         OPTIMIZER DIIS
         MAX_SCF 30
       &END OUTER_SCF
       &SMEAR
         METHOD FERMI_DIRAC
         WINDOW_SIZE 0.007349862
       &END SMEAR
    &END SCF
    &XC
     DENSITY_CUTOFF 1.0e-9
     &XC_GRID
      XC_SMOOTH_RHO SPLINE3
      XC_DERIV SPLINE3_SMOOTH
     &END XC_GRID
     &XC_FUNCTIONAL
      &PBE
      &END PBE
      &END XC_FUNCTIONAL
    &END XC
  &END DFT
  &SUBSYS
    &CELL
      ABC 7.3 7.3 18.65
    &END CELL
    &COORD
 Cu         0.0000000000        0.0000000000        0.0000000000
 Cu         1.8250000000        1.8250000000        0.0000000000
 Cu         0.0000000000        3.6500000000        0.0000000000
 Cu         1.8250000000       -1.8250000000        0.0000000000
 Cu         3.6500000000        0.0000000000        0.0000000000
 Cu        -1.8250000000        1.8250000000        0.0000000000
 Cu         3.6500000000        3.6500000000        0.0000000000
 Cu        -1.8250000000       -1.8250000000        0.0000000000
 Cu        -1.8250000000        0.0000000000        1.8250000000
 Cu         3.6500000000        1.8250000000        1.8250000000
 Cu        -1.8250000000        3.6500000000        1.8250000000
 Cu         3.6500000000       -1.8250000000        1.8250000000
 Cu         1.8250000000        0.0000000000        1.8250000000
 Cu         0.0000000000        1.8250000000        1.8250000000
 Cu         1.8250000000        3.6500000000        1.8250000000
 Cu         0.0000000000       -1.8250000000        1.8250000000
 Cu         0.0027629890        0.1810678691        3.5521582796
 Cu         2.0009703441        1.8306590329        3.7419132473
 Cu         0.0012714586        3.5522008702        3.5509776811
 Cu         1.6331335266       -1.8263840871        3.6506701186
 Cu        -3.6527301762       -0.2667803211        3.6469179283
 Cu        -1.9117113169        1.8216433088        3.8247004427
 Cu        -3.6354479501       4.00316486646        3.6502743039
 Cu        -1.5520623914       -1.7336304355        3.6519202615
  C        -3.6540423726        1.2728466111        5.0359160553
  C        -3.6577740344        2.5275816699        5.0430626704
  H        -3.6575062980        0.6958416548        5.9483529244
  H        -3.6560211188        3.0906730999        5.9596030311
    &END COORD
    &KIND Cu
      BASIS_SET DZVP-MOLOPT-SR-GTH
      POTENTIAL GTH-PBE-q11
    &END KIND
    &KIND C
      BASIS_SET TZV2P-MOLOPT-GTH
      POTENTIAL GTH-PBE-q4
    &END KIND
    &KIND H
      BASIS_SET TZV2P-MOLOPT-GTH
      POTENTIAL GTH-PBE-q1
    &END KIND
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PROJECT cuc2h2_pbe
  PREFERRED_FFT_LIBRARY FFTSG
  RUN_TYPE GEO_OPT
  PRINT_LEVEL LOW
&END GLOBAL
&MOTION
  &CONSTRAINT
    &FIXED_ATOMS
       LIST 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
    &END FIXED_ATOMS
  &END CONSTRAINT
  &GEO_OPT
    MAX_ITER 300
    MAX_FORCE 1.E-7
    OPTIMIZER BFGS
  &END GEO_OPT
&END MOTION


Any help/tips/comments/suggestions would be greatly appreciated.