[Pw_forum] GaAs: band gap with HSE is too large

[Jerónimo Peralta]

Dear all,

I'm using HSE to study bulk GaAs, but even with the parameters cited in the
literature  (number of k points, exx_fraction=0.35, lattice
parameters=10.77, ecutwfc=50 Ry, etc) I'm not able to reproduce the
bandgap. It should give ~1.43 eV.

I'm getting a very large value ~ 3 eV.  Even with smaller values of
exx_fraction =0.15, the gap is still too large. I've tested different norm
conserving PBE pseudopotentials, k point convergence (up to 8x8x8), energy
cutoff convergence, but this discrepancy persists.

I'm computing the DOS directly from a scf run, and it gives ok except for
the value of gap. I would be very grateful if someone has any idea or
information on this. Cheers,

Jeronimo.

-------------------------

A typical input file is:

 &control
    calculation='scf',
    restart_mode='from_scratch',
    prefix='GaAsbulk'
    pseudo_dir = '/home/j/Pseudos-QE',
    outdir='./temp',
    disk_io='high'
 /
 &system
    ibrav=2,
    celldm(1)=10.77,
    nat=2,
    ntyp=2,
    ecutwfc=60.0d0,
    nspin=1,
    occupations='tetrahedra',
    input_dft='hse',
    exx_fraction=0.35
 /

  &electrons
    conv_thr=1d-8,
    mixing_beta=0.7,
    diagonalization='david'
 /

  ATOMIC_SPECIES
   Ga   69.723   Ga.pbe-hgh.UPF
   As   74.92160 As.pbe-hgh.UPF

  ATOMIC_POSITIONS  alat
    Ga 0.0   0.0   0.0
    As 0.25  0.25  0.25

  K_POINTS   automatic
     5 5 5 0 0 0
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