[QE-users] Help: How to optimise lattice c parameter in scf calculation

[Chan, Edmund]

Dear all,

I am currently working on a CH3NH3PbI3 I4/mcm tetragonal structure. I would like to optimise the lattice parameter c using scf calculation after optimising geometry using relax calculation. I tried to fix celldm(1) and changes celldm(3) so that lattice parameter c ranges 10.5-13.5 (true value should be about 12.6, sum of Pb-I-Pb-I-Pb) However, calculations still don't show min energy within the range. still decreasing when celldm(3) keeps decreasing.

Any solution?

Thanks a lot in advance.

#!/bin/sh
####################################################################
#
# define the following variables according to your needs
#
# outdir=temporary_directory_for_large_files
# pseudo_dir=directory_where_pp-files_are_kept
# espresso_dir=top_directory_of_espresso_package
# code : sh run_si_eos
####################################################################
rm -f MAPI_scf.out MAPI.etot_vs_alat
touch MAPI.etot_vs_alat
for alat in 1.2572090494 1.2721758238 1.2871425982 1.3021093726 1.317076147 1.3320429214 1.3470096958 1.3619764701 1.3769432445 1.3919100189 1.4068767933 1.4218435677 1.4368103421 1.4517771165 1.4667438909 1.4817106653 1.4966774397 ; do
# self-consistent calculation
cat > MAPI_scf.in << EOF
&control
calculation='scf',
restart_mode='from_scratch',
prefix='MAPI',
pseudo_dir = '/home/edmund/Quantum-Espresso/pseudo/SSSP_Acc/PBESOL/',
outdir='/home/edmund/Quantum-Espresso/Tutorial/tmp/'
/
&system
ibrav= 6, celldm(1) = 16.703665958 , celldm(3) = $alat , nat= 12, ntyp= 5,
ecutwfc = 70,
/
&electrons
electron_maxstep = 5000,
mixing_beta = 0.3,
conv_thr = 1.0d-6,
/
&ions
ion_dynamics="bfgs",
/
ATOMIC_SPECIES
C 12.01070 c_pbesol_v1.2.uspp.F.UPF
H 1.00794 H.pbesol-rrkjus_psl.0.1.UPF
N 14.00670 N.pbesol-theos.UPF
Pb 207.20000 Pb.pbesol-dn-kjpaw_psl.0.2.2.UPF
I 126.90450 i_pbesol_v1.uspp.F.UPF
ATOMIC_POSITIONS (alat)
Pb -0.060250864 0.119717291 0.415558090
I -0.007273724 -0.001439398 0.113823814
I 0.267082396 0.174145023 0.503051646
I -0.111188287 -0.164962141 0.584095713
C 0.535192046 0.927588487 0.796494424
H 0.581905016 1.042275920 0.809533204
H 0.580744698 0.877063608 0.692556190
H 0.570638845 0.855097719 0.891131917
N 0.366943691 0.939129847 0.789578969
H 0.318073687 0.834961464 0.773620510
H 0.328759438 1.011781981 0.698437223
H 0.325773058 0.986440200 0.887518302
K_POINTS automatic
1 1 1 0 0 0
EOF
pw.x < MAPI_scf.in > MAPI_scf.out
# extract Etot from output
etot=`grep -e ! MAPI_scf.out | awk '{print $(NF-1)}'`
echo $alat $etot >> MAPI.etot_vs_alat
done



Kind regards,

Edmund Chan
________________________________________________
Edmund Chan
PhD Renewable Energy Student
Environment & Sustainablity Institute
College of Engineering, Mathematics and Physical Sciences
University of Exeter, Penryn Campus
Penryn, Cornwall
United Kingdom
TR10 9FE

Tel: +44 (0)7455 235 701
Email: thc208 at exeter.ac.uk<mailto:thc208 at exeter.ac.uk>
LinkedIn: https://uk.linkedin.com/in/edmundchan1
[uoe]

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