[QE-users] Energy of isolated atom of CaO
Lorenzo Paulatto
paulatz at gmail.com
Sat Jun 27 16:09:10 CEST 2020
As I said before, even if you manage to converge this calculation, you
will not get the binding energy of CaO. If you are lucky, you may get
the energy required to disintegrate the compound, which is really not
the same thing.
Furthermore, putting two atoms in a cell and pulling them far apart is a
guaranteed way to run into DFT shortcomings. The two species may want to
be charged with fractionary charge (ie. Ca^1.5+ and O^1.5-) which do not
exist as isolated ions. Finally, the long range 1/r electrostatic
interaction will never converge.
cheers
On 6/27/20 1:25 PM, Pooja Vyas wrote:
> The other way I tried computing isolated energy of Ca and O, is using
> the following separate inputs for Ca and O. Are the input scripts valid?
> The energies got converged for the following scripts.
>
> On Sat, Jun 27, 2020 at 4:45 PM Pietro Delugas <pdelugas at sissa.it
> <mailto:pdelugas at sissa.it>> wrote:
>
> 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 <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows 10
>
> __ __
>
> *From: *Pooja Vyas <mailto:poojavyas595 at gmail.com>
> *Sent: *Saturday, June 27, 2020 11:56 AM
> *To: *Quantum ESPRESSO users Forum
> <mailto:users at lists.quantum-espresso.org>
> *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
> <mailto: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 <https://go.microsoft.com/fwlink/?LinkId=550986>
> for Windows 10
>
> *From: *Pooja Vyas <mailto:poojavyas595 at gmail.com>
> *Sent: *Friday, June 26, 2020 8:12 AM
> *To: *Quantum ESPRESSO users Forum
> <mailto:users at lists.quantum-espresso.org>
> *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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--
Lorenzo Paulatto - Paris
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