[Pw_forum] under estimation of band gap by B3LYP

[MSaqlain]

Dear Users

I have been performing some test calculations. However, with QE, B3LYP 
functional and NC pseudopotentials, I could not reproduce the same band 
gap as reported in literature. Here I am reproducing the input file. any 
comments to improve the band gap? Which parameters needed improvement?

  &CONTROL
                        title = 'MaPbI' ,
                  calculation = 'scf' ,
                 restart_mode = 'from_scratch' ,
                       outdir = '/home/saqlain/tempo' ,
                       wfcdir = '/home/saqlain/tempo' ,
                   pseudo_dir = '/home/saqlain/psp' ,
                       prefix = 'b3lyp' ,
  /
  &SYSTEM
                        ibrav = 0,
                    celldm(1) = 1.8897265,
                          nat = 12,
                         ntyp = 5,
                      ecutwfc = 50 ,
                    input_dft = 'b3lyp' ,
                  occupations = 'smearing' ,
                      degauss = 0.0001 ,
                     smearing = 'marzari-vanderbilt' ,
                     ecutfock = 30 ,
             exxdiv_treatment = 'none' ,
        x_gamma_extrapolation = .false. ,
                         nqx1 = 1 ,
                         nqx2 = 1 ,
                         nqx3 = 1 ,
  /
  &ELECTRONS
  /
CELL_PARAMETERS alat=
      5.834378366   -0.000211726    0.108920456
     -0.000213390    5.806855246   -0.000143936
      0.110146117   -0.000149302    5.840640322
ATOMIC_SPECIES
     C   12.00000  C.pbe-hgh.UPF
     H    1.00000  H.pbe-hgh.UPF
     N   15.00000  N.pbe-hgh.UPF
     I  126.90000  I.pbe-hgh.UPF
    Pb  207.20000  Pb.pbe-hgh.UPF
ATOMIC_POSITIONS crystal
     C      0.899741813    0.999991644    0.939354291
     N      0.116681857    0.999940194    0.066032205
     H      0.942935032    0.999553134    0.756571178
     H      0.803255510    0.154306973   -0.013215230
     H      0.802828226    0.846094729   -0.012606338
     H      0.216099629    0.144436130    1.027340470
     H      0.215788061    0.855133747    1.027684059
     H      0.086425041    0.000193283    0.241051451
    Pb      0.474903357    0.499901389    0.490387142
     I      0.462890134    0.499954443    0.989933585
     I      0.482308382   -0.000094786    0.507160765
     I      0.974122976    0.499891124    0.476094414
K_POINTS automatic
   2 2 2   1 1 1

Regards

Msaqlain

Bilkent Uni. Ankara