[CP2K-user] [CP2K:18397] Improving convergence for bulk Iron (bcc Fe)

[Бранислав Миловановић]

Dear CP2K users,

I'm struggling with convergence for bulk Fe, i.e. 3x3x3 supercell 
containing 54 Fe atoms. I wanted to simulate adsorption of different 
organic molecules on Fe(100) slab later, so this is my starting point.

During GEO_OPT or CELL_OPT runs I sporadically encounter SCF issues like 
this:
...
    33 Broy./Diag. 0.70E+00    2.7     1.02510462     -7902.0344477276 
 2.42E+01
    34 Broy./Diag. 0.70E+00    2.7     1.02694146     -7882.2903511652 
 1.97E+01
    35 Broy./Diag. 0.70E+00    2.7     1.02572163     -7833.4164745080 
 4.89E+01
    36 Broy./Diag. 0.70E+00    2.7     1.02859994     -7878.1467068004 
-4.47E+01
    37 Broy./Diag. 0.70E+00    2.7     1.02924599     -7812.2513589335 
 6.59E+01
...

and here is my DFT section:

 &DFT
    BASIS_SET_FILE_NAME ${DIR}/BASIS_MOLOPT
    POTENTIAL_FILE_NAME ${DIR}/GTH_POTENTIALS
    UKS .TRUE.
    MULTIPLICITY 123
    RELAX_MULTIPLICITY 0.1
    CHARGE 0
    EXCITATIONS NONE
    PLUS_U_METHOD MULLIKEN          # LOWDIN, MULLIKEN_CHARGES
    &SCF
      MAX_SCF 300
      EPS_SCF 1.0E-6
      SCF_GUESS RESTART
      ADDED_MOS 200
      NOTCONV_STOPALL .FALSE.
      CHOLESKY RESTORE
      &DIAGONALIZATION
        ALGORITHM  STANDARD
        EPS_ADAPT 0.0                 # Default 0.0
        MAX_ITER 2                    # Default 2
      &END DIAGONALIZATION
      &MIXING
        METHOD BROYDEN_MIXING
        ALPHA 0.1                    # Default 0.4
        BETA 1.2                      # Default 0.5
        NBUFFER 6
         NMIXING 2
        NSKIP 0
      &END MIXING
      &SMEAR
        ELECTRONIC_TEMPERATURE [K] 500
        METHOD FERMI_DIRAC
      &END SMEAR
      &PRINT
        &RESTART
          BACKUP_COPIES 0
        &END RESTART
      &END PRINT
    &END SCF
    &MGRID
      NGRIDS 4
      CUTOFF 500
      REL_CUTOFF 50
    &END MGRID
    &QS
      METHOD GPW
      EPS_DEFAULT 1.0E-12           # Default 1.0E-10
      EXTRAPOLATION  ASPC           # Default
      EXTRAPOLATION_ORDER 3         # Default
    &END QS
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
      &VDW_POTENTIAL
        POTENTIAL_TYPE  PAIR_POTENTIAL
        &PAIR_POTENTIAL
          R_CUTOFF 1.0583544171800002E+01         # Default
          TYPE DFTD3
          PARAMETER_FILE_NAME ${DIR}/dftd3.dat
          REFERENCE_FUNCTIONAL PBE
        &END PAIR_POTENTIAL
      &END VDW_POTENTIAL
#      &XC_GRID
#        XC_SMOOTH_RHO NN10
#        XC_DERIV SPLINE2_SMOOTH
##        USE_FINER_GRID F
#      &END XC_GRID
    &END XC
  &END DFT

What are your thoughts about parameters that I use? Do I set MAGNETIZATION, 
MULTIPLICITY and RELAX_MULTILIPLICITY correctly?

I followed the instructions from the previous discussions here in group and 
assembled the attached input file. Also, I looked for discussions regarding 
metallic systems including Fe such as:
https://groups.google.com/g/cp2k/c/ugkJLz4PSSI/m/C-ProBR6BwAJ

I have an experience with the CP2K and molecular systems but not for solid 
state calculations.
Also, I have a couple of questions:
1) How does CP2K copes with SYMMETRY set to .TRUE. Is it better to leave 
system to break symmetry?
2) Is it good to use XC_SMOOTH_RHO to smooth XC grid in this case?

Thanks in advance,
Branislav
 

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