cutoff-convergence

[Akshay Malik]

Dear all,

I am trying to do cutoff-convergence for my system but it is only converging up to two digits after the decimal point.

Please suggest some method by which I can get converged energy up to 6 decimals. 

# Grid cutoff vs total energy

# Date: Thu Oct 10 16:37:32 IST 2019
# PWD: /home/space/cp2k/cutoff-convergence
# REL_CUTOFF = 60
# Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on grid 3 | NG on grid 4
     50.00  -1337.8915343935  668903   50882     240       0
    100.00  -1351.0266889654  1216132  286203   11290       0
    150.00  -1351.6349634609  1071797  364690   75938    1200
    200.00  -1351.6825629692  975942  418150  115933    3600
    250.00  -1351.6992612267  875755  439820  192650    5400
    300.00  -1351.6990099247  791971  424161  286203   11290
    350.00  -1351.6961310939  735698  431201  323555   23171
    400.00  -1351.6944391280  687700  428173  341928   55824
    450.00  -1351.6933108152  644645  427152  364690   77138

    500.00  -1351.6931016574  603223  441589  368145  100668

I am using this cp2k file section for calculating energy:

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME  GTH_BASIS_SETS
    POTENTIAL_FILE_NAME  GTH_POTENTIALS
    &MGRID
      NGRIDS 4
      CUTOFF LT_cutoff
      REL_CUTOFF LT_rel_cutoff
    &END MGRID
    &QS
      EPS_DEFAULT 1.0E-10
    &END QS
    &SCF
      SCF_GUESS ATOMIC
      EPS_SCF 1.0E-6
      MAX_SCF 1
      ADDED_MOS 10
      CHOLESKY INVERSE
      &SMEAR ON
        METHOD FERMI_DIRAC
        ELECTRONIC_TEMPERATURE [K] 333
      &END SMEAR
      &DIAGONALIZATION
        ALGORITHM STANDARD
      &END DIAGONALIZATION
      &MIXING
        METHOD BROYDEN_MIXING
        ALPHA 0.4
        BETA 0.5
        NBROYDEN 8
      &END MIXING
    &END SCF
     &XC
      &XC_FUNCTIONAL BLYP
      &END
    &END
  &END DFT

[Patrick Gono]

Dear Malik,

You might consider further increasing the CUTOFF. Values up to higher triple digits might be necessary to completely converge your energies depending on the system you are simulating.

Yours sincerely, 

Patrick Gono 

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