[QE-users] Energy of isolated atom of CaO

[Pietro Delugas]

Dear Pooja 
I might not have understooo what you want to do. 

Looking at  your input it looks like you are not actually computing the energy of an isolated system, but instead the energy of 
rocksalt CaO. In that case it is not isolated system, remove assume_isolated from the input, use sensible values for alat and the computation should converge. 

Pietro 

Sent from Mail for Windows 10

From: Pooja Vyas
Sent: Saturday, June 27, 2020 11:56 AM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Energy of isolated atom of CaO

I tried the way you suggested, tried replacing "relax" by "scf", however , I still face the same issue: No convergence even after 100 iterations. Following is the input file:

PS: I want to calculate isolated energy of CaO using example05/PW (i.e Martyna-Tuckerman) method.
#!/bin/sh

for a in 30
do

cat > ${a}.in << EOF
&CONTROL
  calculation  = 'relax'
  prefix       = "${a}",
  pseudo_dir   = "/home/userpooja/pv/cohesive/pseudo/",
  outdir       = "/home/userpooja/pv/cohesive/",
/
&SYSTEM
  ibrav     = 1,
  celldm(1) = $a,
  nat       = 2,
  ntyp      = 2,
  ecutwfc   = 100.D0,
  nbnd      = 8
  assume_isolated = 'martyna-tuckerman'
/
&ELECTRONS
  conv_thr    = 1.D-8,
  mixing_beta = 0.7D0,
  startingwfc = 'random'
/
&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

Any kind of help is appreciated.
Thanks and Regards.

On Fri, Jun 26, 2020 at 11:58 AM Pietro Delugas <pdelugas at sissa.it> wrote:
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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