[CP2K-user] Band Gap Error for substituted compounds

[Nicholas Winner]

Just to be clear, as I'm having a little trouble following you're message: 
the expected outcome is that Sr substitution will decrease the band gap; 
you substituted 2 Sr atoms in place of Ba, and this increased the band gap; 
when you do a static calculation (no relaxation) the band gap does 
decrease, but when you enable relaxation then the band gap increases.

Are all three of those points correct?

The next thing I would ask, if that is correct, is to see the output file.
On Tuesday, October 27, 2020 at 8:02:01 AM UTC-7 a... at g.clemson.edu wrote:

> 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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