Bulk modulus of silicon with CP2K

[leila]

Hi all, 

I simulated the silicon with 64 atoms and calculated the energy-volume plot 
and fitted with murnaghan.
I found the lattice parameter 5.48 A ( lattice parameter in experiment is 
5.44 A), That is OK but the bulk modulus is 63 GPa that is very low. (B_exp 
= 100 GPa)
I really don' t know why cp2k gets B so low???

I tried with DZVP basis set and PBE functional with 280 Ryd cut off for 
density.
I also checked with TZVP, it is not changing so much. It is 66 GPa.
Can anybody help me with that?
You can find my inputfile in below.

&GLOBAL
  PROJECT si64-10.88A
  PRINT_LEVEL LOW
  RUN_TYPE GEO_OPT
&END GLOBAL
&MOTION
  &CELL_OPT
    TYPE GEO_OPT
    OPTIMIZER CG
    MAX_ITER 20
    EXTERNAL_PRESSURE [bar] 1.0
    MAX_DR 0.02
    RMS_DR 0.01
    MAX_FORCE 0.0002
    RMS_FORCE 0.0001
    KEEP_ANGLES
    &CG
      &LINE_SEARCH
        TYPE 2PNT
        &2PNT
        &END
      &END
    &END
  &END
  &GEO_OPT
    MAX_ITER 200
    MINIMIZER BFGS
  &END
  &PRINT
    &STRESS
    &END STRESS
    &RESTART
      &EACH
        CELL_OPT 1
      &END
    &END
  &END
&END
&FORCE_EVAL
  METHOD QS
  STRESS_TENSOR ANALYTICAL
  &DFT
    BASIS_SET_FILE_NAME ./BASIS_MOLOPT
    POTENTIAL_FILE_NAME ./GTH_POTENTIALS
    &MGRID
      CUTOFF 280
    &END MGRID
    &QS
      METHOD GPW
    &END QS
    &SCF
      SCF_GUESS RESTART
      MAX_SCF 20
      EPS_SCF 1.0e-5
      &OUTER_SCF
      EPS_SCF 1.0E-5
      &END
      &OT ON
#        MINIMIZER DIIS
         ROTATION
      &END OT
      &PRINT
        &RESTART
          BACKUP_COPIES 0
        &END RESTART
      &END PRINT
    &END SCF
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
      &vdW_POTENTIAL
         DISPERSION_FUNCTIONAL PAIR_POTENTIAL
         &PAIR_POTENTIAL
            TYPE DFTD3
            CALCULATE_C9_TERM .TRUE.
            REFERENCE_C9_TERM .TRUE.
            LONG_RANGE_CORRECTION .TRUE.
            PARAMETER_FILE_NAME ./dftd3.dat
            REFERENCE_FUNCTIONAL PBE
            R_CUTOFF 8.
            EPS_CN 0.01
         &END PAIR_POTENTIAL
      &END vdW_POTENTIAL
    &END XC
  &END DFT
  &SUBSYS
    &TOPOLOGY
      COORD_FILE_NAME ./GEOMETRY.xyz
      COORDINATE XYZ
#      CONNECTIVITY OFF
    &END TOPOLOGY
    &KIND Si
      BASIS_SET DZVP-MOLOPT-SR-GTH
#      BASIS_SET SZV-MOLOPT-SR-GTH
#       BASIS_SET TZVP-MOLOPT-GTH
      POTENTIAL GTH-PBE-q4
    &END
    &CELL
      ABC    10.88  10.88 10.88
    &END
  &END SUBSYS
 &END
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