Dear Mohammad,
I suggest you do the following exercise:
Compute the band structure of 54 atom of Si with a similar setting to
the one of your present calculation. Does it have direct gap ? compute
the DOS.
Compute the band structure of Silicon in the 2-atom unit cell
with celldm(1) = 10.2623467, k_points (automatic) set to 15 15 15 0 0 0
Does it have a direct gap ? compute the DOS
Compare total energy, band structure and DOS in the two cases.
Which calculation is correct ?
stefano
On 01/08/2016 20:19, Mohammad Abu Raihan Miah wrote:
Hi all,
I am currently simulating band diagram for Phosphorus doped Silicon. I
am using 53 Si atoms and 1 P atom for computation. When I computed the
band diagram, it resulted in direct band gap, which is not true case
for Silicon. I have not relaxed the system.
My input file is as follows,
&control
calculation = 'scf',
restart_mode='from_scratch',
verbosity = 'high',
prefix = 'Silicon_P_54_relax',
tstress = .true.,
tprnfor = .true.,
pseudo_dir = '.',
outdir = 'out_P_rel',
wf_collect=.true.,
max_seconds=10800,
/
&system
ibrav=2,
celldm(1) = 30.787040,
nat=54,
ntyp=2,
ecutwfc=50,
ecutrho=400.0d0,
input_dft='PBE',
nbnd=120,
occupations='smearing',
degauss=0.05,
/
&electrons
diagonalization='david',
mixing_mode = 'plain',
mixing_beta = 0.7,
conv_thr = 1.0d-6,
/
ATOMIC_SPECIES
Si 28.085500 Si.pbe-n-rrkjus_psl.0.1.UPF
P 30.973800 P.pbe-n-rrkjus_psl.0.1.UPF
ATOMIC_POSITIONS (alat)
Si 0.000000 0.000000 0.000000
..................................
P 0.083333 0.083333 0.083333
.............................
Si 0.750000 0.750000 0.750000
K_POINTS (automatic)
5 5 5 0 0 0
Could anyone please explain the reason behind this change from
indirect to direct bandgap? Or any suggestion to solve this problem?
Thank you very much.
Best,
--
Mohammad Abu Raihan Miah
PhD Student
Department of Electrical and Computer Engineering (ECE)
<http://www.ece.ucsd.edu/>
University of California, San Diego <http://www.ucsd.edu/>
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