[CP2K:4550] Bulk modulus of silicon with CP2K

[hut... at pci.uzh.ch]

Hi

I would guess that your calculation is not yet converged
with respect to

1) the basis set
2) the k-points. I would use a small unit cell and then
   the MULTIPLE_UNIT_CELL keyword to check for convergence
3) the cutoff, you are probably close here (REL_CUTOFF 80, just to be sure)
   I would still use the REF_CELL keyword in order to do constant
   number of grid point calculations
4) the dispersion correction will change the reference PBE value

regards

Juerg
 

--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich               E-mail:  hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
---------------------------------------------------------------

-----cp... at googlegroups.com wrote: -----
To: cp... at googlegroups.com
From: leila salimi 
Sent by: cp... at googlegroups.com
Date: 08/12/2013 03:05PM
Subject: Re: [CP2K:4550] Bulk modulus of silicon with CP2K

Dear Juerg, 

Thanks for your answer.
1) the PBE value for B is 89 GPa.
2) I also tried with higher cutoff and REF_CUTOFF, but it didn't change.

 
&MGRID
      NGRIDS 8
      CUTOFF 500
      REL_CUTOFF  60
    &END MGRID


On Mon, Aug 12, 2013 at 2:40 PM,  <hut... at pci.uzh.ch> wrote:
 Hi
 
 two things to do:
 1) What is the official PBE value for this quantity?
 2) Use a REF_CELL and a high enough cutoff (has to be tested)
    in order to get a smooth enough pressure curve
 
 regards
 
 Juerg
 
 --------------------------------------------------------------
 Juerg Hutter                         Phone : ++41 44 635 4491
 Physical Chemistry Institute   FAX   : ++41 44 635 6838
 University of Zurich               E-mail:  hut... at pci.uzh.ch
 Winterthurerstrasse 190
 CH-8057 Zurich, Switzerland
 ---------------------------------------------------------------
 
 -----cp... at googlegroups.com wrote: -----
 To: cp... at googlegroups.com
 From: leila
 Sent by: cp... at googlegroups.com
 Date: 08/12/2013 11:57AM
 Subject: [CP2K:4549] Bulk modulus of silicon with CP2K
 

 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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