Dear Quantum Espresso users,
Using QE6.5, I did an HSE scf calculation on the rutile TiO2 and found it failed to reproduce the bandgap (much smaller than the values reported or calculated with VASP code). Then I did a test of Si and checked the gaps at the gamma point. (Although silicon is an indirect bandgap semiconductor, this doesn't matter to illustrate the problem.) The result shows that the gaps at gamma point calculated with PBE and HSE functionals are 0.72eV and 0.70eV, respectively. For comparison, the calculation using VASP code shows values of 0.75eV and 1.34eV, with PBE and HSE functionals respectively.
I don't know whether I made any mistake during this calculation and I hope you can help me with this problem. The input file is attached as below. Any advice to improve the calculation is also welcomed. Thanks a lot!
&CONTROL
title = 'Si'
calculation = 'scf'
restart_mode = 'from_scratch'
outdir = './1/'
pseudo_dir = './'
prefix = 'C'
tstress = .true.
tprnfor = .true.
wf_collect=.true.
disk_io = 'low'
verbosity = 'high'
/
&SYSTEM
ibrav = 0
nat = 8
ntyp = 1
ecutwfc = 90
ecutfock = 180
nosym = .true.
tot_charge = 0
!nbnd=20
occupations='smearing', smearing='gaussian', degauss=0.002
input_dft = 'hse'
nqx1 = 1
nqx2 = 1
nqx3 = 1
exx_fraction = 0.25
/
&ELECTRONS
diagonalization = 'david'
conv_thr = 1.0D-7
adaptive_thr = .true.
mixing_beta = 0.7
electron_maxstep=100
/
&IONS
ion_dynamics = 'bfgs'
/
ATOMIC_SPECIES
Si 28.086 Si_ONCV_PBE_sr.upf
K_POINTS
10
0.00000000000000 0.00000000000000 0.00000000000000 1
0.25000000000000 0.00000000000000 0.00000000000000 6
0.50000000000000 0.00000000000000 0.00000000000000 3
0.25000000000000 0.25000000000000 0.00000000000000 12
0.50000000000000 0.25000000000000 0.00000000000000 12
0.50000000000000 0.50000000000000 0.00000000000000 3
0.25000000000000 0.25000000000000 0.25000000000000 8
0.50000000000000 0.25000000000000 0.25000000000000 12
0.50000000000000 0.50000000000000 0.25000000000000 6
0.50000000000000 0.50000000000000 0.50000000000000 1
CELL_PARAMETERS bohr
10.3343982983998 0.000000000000000E+000 0.000000000000000E+000
0.000000000000000E+000 10.3343982983998 0.000000000000000E+000
0.000000000000000E+000 0.000000000000000E+000 10.3343982983998
ATOMIC_POSITIONS bohr
Si 0.000000000000000E+000 0.000000000000000E+000 0.000000000000000E+000
Si 0.000000000000000E+000 5.16719914919990 5.16719914919990
Si 5.16719914919990 5.16719914919990 0.000000000000000E+000
Si 5.16719914919990 0.000000000000000E+000 5.16719914919990
Si 7.75079917851337 2.58359957459995 7.75079917851337
Si 2.58359957459995 2.58359957459995 2.58359957459995
Si 2.58359957459995 7.75079917851337 7.75079917851337
Si 7.75079917851337 7.75079917851337 2.58359957459995
Best regards,
Greg Xu
Department of physics, Fudan University.
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