Dear developers,<div>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.</div><div>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.</div><div>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.</div><div>I even tried keeping the symmetry during the cellopt calculations, but still the result was same. The scf guess parameter is set to atomic</div><div>below i attaching the input files for my calculations</div><div>Thanking you in anticipation</div><div>Sincerely </div><div>Afrid.</div><div> </div><div> &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 </div><div> </div>