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

Sat Nov 17 04:08:22 CET 2018

Dear Edmund,

The (1x1x1) k-point mesh is not good enough to get the reliable data for your system.

You may also need to consider the van der Waals correction due to the existence of the large atoms.

Best regards,

Yun

Dr Yun Wang | Senior Lecturer PhD
Centre for Clean Environment and Energy | School of Environment & Science
Griffith University | Gold Coast campus | QLD 4215 | G24 Room 3.36
T +61 7 5552 8358 |  email yun.wang at griffith.edu.au<mailto:yun.wang at griffith.edu.au>

https://experts.griffith.edu.au/academic/yun.wang

Griffith University - CRICOS Provider Number 00233E
PRIVILEGED - PRIVATE AND CONFIDENTIAL

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Chan, Edmund <thc208 at exeter.ac.uk>
Sent: Saturday, November 17, 2018 8:40:02 AM
To: users at lists.quantum-espresso.org
Subject: [QE-users] Help: How to optimise lattice c parameter in scf calculation

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<https://uk.linkedin.com/in/edmundchan1>

[uoe]

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