[Pw_forum] unexpected results after relaxation
Padmaja Patnaik
padmaja_patnaik at yahoo.co.uk
Thu Jun 9 10:28:22 CEST 2011
Dear All
I am plotting density of states for unrelaxed and
relaxed calculations of cubic SiC with B, Al and Ga as substitutional
impurity. Substitutions are done for both Si and C sites separately. The
density plot without relaxation looks OK. But after relaxation the
density plot undergoes a drastic change. I am not able to understand
whats going wrong. Here I am sending the density plots for all the cases
with and without relaxation. In all the figures the top of valence band
is taken as zero on the energy axis. Calculations are done with a
supercell of 128 atoms with one single impurity atom in it. The dashed
(purple) line is the Fermi energy. The dotted line shows the calculated
band gap. I am aslo giving here a portion of the relaxed input file
used for calculations.
&control
calculation='relax'
restart_mode='from_scratch',
prefix='sic',
pseudo_dir = '/espresso-4.0.5/pseudo/',
outdir='/tmp/'
tprnfor= .TRUE.
/
&system
ibrav=2, celldm(1) =32.9648, nat=128, ntyp=3,
nspin = 2,
starting_magnetization(1)=0.0,starting_magnetization(2)=0.0,
starting_magnetization(3)=0.0,
ecutwfc = 30.0,
occupations='smearing', smearing='methfessel-paxton', degauss=0.02
/
&electrons
mixing_beta = 0.7
/
&IONS
pot_extrapolation =
"second_order",
wfc_extrapolation = "second_order",
/
ATOMIC_SPECIES
Si 28.086 Si.pz-vbc.UPF
C
12.00 C.pz-vbc.UPF
Al 26.98154 Al.pz-vbc.UPF
As ssen
in figure after relaxation we found mane levels inside band gap at there
is no gap for Al and Ga case. How is this possible? I have also done
for few other impurities and in most of the cases the C site
substitution after relaxation gives multiple levels inside band gap. Can
anybody please clarify whats going wrong?
Thanks in advance.
regards
Padmaja Patnaik
Research Scholar
Dept of Physics
IIT Bombay
Mumbai, India
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