Dear all! I am currently trying to simulate the electronic properties of CsPbBr3 in its low-temperature phase (orthorhombic; a=8.244, b=11.735, c=8.198 angstrom, according to Stoumpos; Cryst. Growth Des. 2013); My principle plan is to follow Radi et al. (arXiv:1405.1706v2), who have done this using Wien2k, muffin-tin potentials. Eventually I want to continue processing this with YAMBO (doesn’t take US PP), so I am using normcons PBE (from the standard repository).
However, the band-gap obtained is really tiny (without SOC, SOC is known to
further reduce the gap in this material); I have done the following:
1) Used the CIF file provided by stoumpos et al to create my unit cell and
double checked with xcrysden -pwi if it turns out properly
2) Tested convergence wrt. Total energy leading to a good compromise with
ecutwfc =60.0 (tested between 30 and 180 Ry) and a unshifted automatic 4x3x4
k-grid (tested up to 16x16x16).
3) Run Relax (gamma only) - scf - bands along G-X-S-R-G
The resulting band structure is in the pdf. The band gap at R is so tiny (0.x
eV) that I am not sure if applying scissors in yambo is justified. I also tried
smaller degauss and fixed occupations to not much success. If someone can spot
an obvious error in my input or has any hint how I can improve my results I
would be very grateful! Thank you in advance for your time and help!
Yours,
Chris
PS: I have also tried a VC-relax which clearly favors a shrinking cell (the
cubic phase of CsPbBr3 for example is a=5.605 A, so the Pnma cell is probably
far away from 0K - how to deal with this problem when trying to do a 300K
phase…?)
My scf input:
&control
calculation = 'scf'
restart_mode='from_scratch',
prefix='cspbbr3',
pseudo_dir = '. /pseudo/',
outdir='./'
wf_collect=.true.
verbosity='high'
/
&SYSTEM
ibrav = 8
celldm(1)= 15.5789
celldm(2)= 1.4235
celldm(3)= 0.9944
nat = 5
ntyp = 3
ecutwfc =60.0
occupations='smearing'
smearing='mp'
degauss=0.002
force_symmorphic=.true.
vdw_corr='grimme-d2'
/
&electrons
diago_full_acc=.true.,
conv_thr=1.0d-8
diagonalization='david'
electron_maxstep=300
/
ATOMIC_SPECIES
Pb 207.20000 Pb.pbe-d-hgh.UPF
Cs 132.90500 Cs.pbe-sp-hgh.UPF
Br 79.90400 Br.pbe-hgh.UPF
ATOMIC_POSITIONS (crystal)
Pb 0.500000000 0.495569542 0.500000000
Cs 0.000000000 -0.000054173 0.000000000
Br 0.000000000 0.496389920 0.500000000
Br 0.500000000 0.002099521 0.500000000
Br 0.500000000 0.496980388 0.000000000
K_POINTS {automatic}
4 3 4 0 0 0
My bands input
nbnd=200 ! include plenty of empty bands for yambo
And
K_POINTS {crystal_b}
5
0.0000000000 0.0000000000 0.0000000000 10 !G
0.5000000000 0.0000000000 0.0000000000 10 !X
0.5000000000 0.5000000000 0.0000000000 10 !S
0.5000000000 0.5000000000 0.5000000000 10 !R
0.0000000000 0.0000000000 0.0000000000 10 !G
Christoph Wolf
Department of Materials Science and Engineering, POSTECH
RIST #3, 3152, San 31 Hyoja-dong, Nam-gu, Pohang, Kyungbuk, 790-784, Republic
of Korea
[http://home.postech.ac.kr/wp-content/themes/postech/images/mail_logo_postech30.png]
30POSTECH
bands.pdf
Description: bands.pdf
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