[QE-users] Energy of isolated atom of CaO

[Pietro Delugas]

Hello 

In ATOMIC_POSITIONS  you need to specify the units that you are  using for the coordinates, if you don’t put anything he program assumes alat units and puts the 2 atoms very far apart. 

If you actually wanted  compute the two separated atoms specifying startingwfc=’random’ in the &electrons name list may help.  In this case I would also chose calculation=’scf’ in &control. 

Regards - Pietro  

Sent from Mail for Windows 10

From: Pooja Vyas
Sent: Friday, June 26, 2020 8:12 AM
To: Quantum ESPRESSO users Forum
Subject: [QE-users] Energy of isolated atom of CaO

Dear users,
I want to calculate cohesive energy of CaO. I'm using cluster_example/PW which uses assume_isolated = 'martyna_tuckerman' . Following is my input script:

#!/bin/sh
for a in 30
do
cat > ${a}.in << EOF
&CONTROL
  calculation  = 'relax'
  prefix       = "${a}",
  pseudo_dir   = "/home/user/pv/cohesive/pseudo/",
  outdir       = "/home/user/pv/cohesive/",
/
&SYSTEM
  ibrav     = 1,
  celldm(1) = $a,
  nat       = 2,
  ntyp      = 2,
  ecutwfc   = 100.D0,
  assume_isolated = 'martyna-tuckerman'
/
&ELECTRONS
  conv_thr    = 1.D-8,
  mixing_beta = 0.7D0,
/
&IONS
/
ATOMIC_SPECIES
Ca  40.078  Ca.pbe-nsp-van.UPF
O  15.999  O.pbe-van_ak.UPF
ATOMIC_POSITIONS 
Ca 0.0 0.0 0.0
O  0.5 0.5 0.5
K_POINTS Gamma

EOF

mpirun -np 40 -machinefile x1 /apps/codes/qe/6.4/bin/pw.x < ${a}.in > ${a}.out
done
done

My lattice constant is around 8 a.u , so I assumed the box size to be 3 times of it. But when I run the script, the convergence was not achieved even after 100 iterations. Then I tried to take small box size of about 16 bohr. That too didn't work. Then I even tried reducing ecutwfc and mixing_beta..but same error was obtained. Can anyone suggest what can I do to resolve the issue?
Any kind of help is appreciated.
Thanks and regards.

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