[CP2K-user] Band Gap Error for substituted compounds

[AFRID MAZHAR SHIRSEKAR]

Dear developers,
I have been trying to study the effect on band gap, when substitutions are 
implemented on BaTiO3 structure. My methodology is that i generate a 2 x 2 
x 2 supercell of BaTiO3 and substitute 2 Sr atoms in the Ba positions, and 
then i conduct cell optimization on the new structure, and then i used the 
converged coordinates file and the unit cell parameters  from the output 
to  evaluate the band gap.
The band gap for BaTiO3 is around 3.2  ev, i used 37%hfx to approximate the 
bandgap closer to experimental one for BaTiO3 structure, but when the 
substitutions are implemented the calculation overestimates the band gap by 
1 ev (4.2ev) which was expected to decrease from the initial value.
i calculated the bandgap without performing the cellopt and just 
substituted the Sr atoms in the coord file, and the result was in 
accordance with my hypothesis, ie decrease in the band gap.
I even tried keeping the symmetry during the cellopt calculations, but 
still the result was same. The scf guess parameter is set to atomic
below i attaching the input files for my calculations
Thanking you in anticipation
Sincerely 
Afrid.

&GLOBAL

  PROJECT perovskite_bandgap

  RUN_TYPE ENERGY 

  PRINT_LEVEL MEDIUM

&END GLOBAL


&FORCE_EVAL

  METHOD Quickstep

  &DFT

    BASIS_SET_FILE_NAME  BASIS_file 

    POTENTIAL_FILE_NAME  POTENTIALS_file

    BASIS_SET_FILE_NAME  BASIS_ADMM_MOLOPT

    BASIS_SET_FILE_NAME  BASIS_ADMM

    WFN_RESTART_FILE_NAME afrid-test-1.restart


    &PRINT                

       &MO_CUBES

       WRITE_CUBE .FALSE. 

       NHOMO 1            

       NLUMO 1            

       &END

    &END

    &QS

     METHOD GPW

     EXTRAPOLATION PS 

     EXTRAPOLATION_ORDER 3

     EPS_DEFAULT 1.0E-10              #E-6

    &END QS

    &POISSON

      PERIODIC XYZ

    &END POISSON

    &SCF

      SCF_GUESS ATOMIC

      EPS_SCF 1.0E-6                  #E-7

      MAX_SCF 30

      !EPS_LUMO 1.00000000E-005

      !CHOLESKY INVERSE

      

      &OT

       PRECONDITIONER FULL_SINGLE_INVERSE        #FULL ALL

       MINIMIZER DIIS              # minimiser cg

       ALGORITHM IRAC             #no algorithm before

       ENERGY_GAP 0.01

      &END

      &OUTER_SCF 

MAX_SCF 20

EPS_SCF 1e-06

      &END OUTER_SCF 

      &MIXING

        METHOD BROYDEN_MIXING

        ALPHA 0.2

        BETA 1.5

        NBROYDEN 8

      &END MIXING

    &END SCF

    &MGRID 

CUTOFF 940

REL_CUTOFF 80

NGRIDS 5

PROGRESSION_FACTOR 3

    &END MGRID

    &XC

      &XC_FUNCTIONAL PBE

       &PBE                  

           SCALE_X 0.630

           SCALE_C 1.0

       &END

      &END XC_FUNCTIONAL

      &VDW_POTENTIAL

        POTENTIAL_TYPE pair_potential

        &PAIR_POTENTIAL

          TYPE DFTD3(BJ)

          PARAMETER_FILE_NAME dftd3.dat

          REFERENCE_FUNCTIONAL PBE

        &END PAIR_POTENTIAL

      &END VDW_POTENTIAL

      &HF

        FRACTION 0.370         

        &SCREENING            

          EPS_SCHWARZ 1.0E-7

          !SCREEN_ON_INITIAL_P TRUE  

        &END                        

        &MEMORY

          MAX_MEMORY 7500   

        &END

        &INTERACTION_POTENTIAL      

          POTENTIAL_TYPE TRUNCATED  

          CUTOFF_RADIUS 3         

          T_C_G_DATA ./t_c_g.dat    

        &END                        

      &END

    &END XC

    &AUXILIARY_DENSITY_MATRIX_METHOD 

ADMM_PURIFICATION_METHOD NONE

METHOD BASIS_PROJECTION

&END AUXILIARY_DENSITY_MATRIX_METHOD

  &END DFT


  &SUBSYS

    &CELL

      

      A 8.043 0.000 0.000

      B 0.014 7.998 0.000

      C 0.014 0.019 7.998

     

      ALPHA_BETA_GAMMA 89.867 89.900 89.900

      

      

      MULTIPLE_UNIT_CELL 1 1 1

    &END CELL

    

    &TOPOLOGY

      COORD_FILE_FORMAT XYZ

      COORD_FILE_NAME BaTi03-cellopt-pos-1-converged.xyz

      MULTIPLE_UNIT_CELL 1 1 1

      

    &END TOPOLOGY

    &KIND Ba

      ELEMENT   Ba

      BASIS_SET DZVP-MOLOPT-SR-GTH-q10

      POTENTIAL GTH-PBE-q10

      BASIS_SET AUX_FIT cFIT10

    &END KIND

    &KIND Ti

      ELEMENT   Ti

      BASIS_SET DZVP-MOLOPT-SR-GTH-q12

      POTENTIAL GTH-PBE-q12

      BASIS_SET AUX_FIT cFIT10

    &END KIND

    &KIND O

      ELEMENT   O

      BASIS_SET DZVP-MOLOPT-SR-GTH-q6

      POTENTIAL GTH-PBE-q6

      BASIS_SET AUX_FIT FIT9

    &END KIND

    &KIND Sr 

      ELEMENT   Sr

      BASIS_SET DZVP-MOLOPT-SR-GTH-q10

      POTENTIAL GTH-PBE-q10

      BASIS_SET AUX_FIT cFIT10

    &END KIND

    &KIND Pb

      BASIS_SET DZVP-MOLOPT-SR-GTH-q4

      POTENTIAL GTH-PBE-q4

      BASIS_SET AUX_FIT cFIT9

    &END KIND

    &KIND Ca

      BASIS_SET DZVP-MOLOPT-SR-GTH-q10

      POTENTIAL GTH-PBE-q10

      BASIS_SET AUX_FIT cFIT10

    &END KIND

  &END SUBSYS


&END FORCE_EVAL



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