[Pw_forum] Energy of O2 in its triplet ground state

[Lorenzo Paulatto]

Dear Shuai,
I've attached the input files to do it in "the right way". You can see 
three ways to compute the energy of the isolated Oxygen atom, but only 
the one that gives the lowest energy is correct! Try to see for yourself 
what are the differences between the three cases, and please ask if you 
have any doubt.

Also for the O2 molecules theer are some tricks to use, again ask if you 
have doubts.

Finally, note that the O-O oxygen in the molecule is very small, smaller 
that the pseudisation radius normally used in pseudopotential. This 
means that if you want to get really accurate results you will have to 
find or generate an especially hard pseudopotential.

kind regards



On 17/01/15 07:53, Shuai wrote:
> Dear all,
>
> I want to calculate the energy of the O2 in its triplet ground state. 
> I have searched on the sites 
> (http://qe-forge.org/pipermail/pw_forum/2012-July/099147.html) and do 
> some tentative calculations.
>
> Firstly, I calculated the two O atoms in a enough large box. the input 
> file is:
>
>  &control
>    calculation    = 'relax'
>    prefix    = 'O2'
>    pseudo_dir    = '/'
>    outdir    = '/'
>  /
>  &system
>    ibrav = 1, celldm(1) = 30.0
>    nat = 2, ntyp = 1,
>    ecutwfc = 35, ecutrho = 280
>    occupations = 'smearing', degauss = 0.01
>    nspin = 2, starting_magnetization(1) = 0.3
>  /
>  &electrons
>    mixing_mode    = 'plain'
>    mixing_beta    = 0.3
>    conv_thr    = 1.0d-8
>    electron_maxstep = 200
>  /
>  &ions
>    ion_dynamics    = 'bfgs'
>  /
> ATOMIC_SPECIES
> O    15.999    O.pbe-n-kjpaw_psl.1.0.0.UPF
> ATOMIC_POSITIONS {angstrom}
> O    5.000576334    5.029093041    5.029093041
> O    5.009423666    5.870906959    5.870906959
> K_POINTS {gamma}
>
> Secondly, I calculated the single O atom.
>
> Finally, I calculated the binding energy of O2 by "2 x single O atom 
> energy - O2 eneygy". But I am not sure it is correct or not. My 
> question is if the "binding energy" is close to the experimental value 
> ~ 5.7 eV, does it mean that the calculated energy of O2 is accurate?
>
> Thanks in advance.
>
> Sincerely,
>
> S. Zhao
> --
> PhD candidate
> Graduate School of Life Science and Systems Engineering
> Kyushu Institute of Technology, Japan
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
+33 (0)1 44 275 084 / skype: paulatz
http://www-int.impmc.upmc.fr/~paulatto/
23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05

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O1
 &control
    calculation = 'scf'
    prefix='o1',
    pseudo_dir = '../hard'
    outdir='/home/paulatto/tmp'
    disk_io='low'
 /
 &system
    ibrav=  2, celldm(1) =25.0, nat=  1, ntyp= 1, nelec=,
    ecutwfc=70
    !ecutrho=180,
    occupations = 'from_input'
    nspin = 1
    nbnd = 7
    nosym = .true.
 /
 &electrons
    conv_thr =  1.0d-6
 /
ATOMIC_SPECIES
 O   1.000  O.pbe-paw_kj.UPF 
ATOMIC_POSITIONS {alat}
O   0.0   0.0   0.0
OCCUPATIONS
2. 1.333333333333 1.333333333333 1.333333333333   0. 0. 0. 
K_POINTS {gamma}
  
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O2
 &control
    calculation = 'relax'
    prefix='o2',
    pseudo_dir = '../hard'
    outdir='/home/paulatto/tmp'
 /
 &system
    ibrav=  2, celldm(1) =25.0, nat=  2, ntyp= 1, 
    ecutwfc=70
    !ecutrho=150,
    occupations = 'smearing'
    smearing = 'gaussian'
    degauss = 0.005
    nspin = 2
    starting_magnetization(1) = +.1
    starting_magnetization(1) = -.1
 /
 &electrons
    conv_thr =  1.0d-6
    mixing_ndim = 8 
/
 &ions
    ion_dynamics = 'bfgs'
 /
ATOMIC_SPECIES
 O   16.000  O.pbe-paw_kj.UPF
ATOMIC_POSITIONS {bohr}
O        0.673775191   0.673775191   0.673775191
O       -0.673775191  -0.673775191  -0.673775191
K_POINTS {gamma}
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O1
 &control
    calculation = 'scf'
    prefix='o1_pol'
    pseudo_dir = '../hard'
    outdir='/home/paulatto/tmp'
    disk_io='low'
 /
 &system
    ibrav=  2, celldm(1) =25.0, nat=  1, ntyp= 1, nelec=,
    ecutwfc=70
    !ecutrho=150,
    occupations = 'from_input'
    nspin = 2
    nbnd = 7
    nosym = .true.
 /
 &electrons
    conv_thr =  1.0d-6
 /
ATOMIC_SPECIES
 O   1.000  O.pbe-paw_kj.UPF 
ATOMIC_POSITIONS {alat}
O   0.0   0.0   0.0
OCCUPATIONS
1. 1. 1. 1.   0. 0. 0. 
1. 1. 0. 0.    0. 0. 0.
K_POINTS {gamma}
  
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O1
 &control
    calculation = 'scf'
    prefix='o1_spin'
    pseudo_dir = '../hard'
    outdir='/home/paulatto/tmp'
    disk_io='low'
 /
 &system
    ibrav=  2, celldm(1) =25.0, nat=  1, ntyp= 1, nelec=,
    ecutwfc=70
    !ecutrho=150,
    occupations = 'from_input'
    nspin = 2
    nbnd = 7
    nosym = .true.
 /
 &electrons
    conv_thr =  1.0d-6
    mixing_ndim = 1
 /
ATOMIC_SPECIES
 O   1.000  O.pbe-paw_kj.UPF 
ATOMIC_POSITIONS {alat}
O   0.0   0.0   0.0
OCCUPATIONS
1. 1. 1. 1.   0. 0. 0. 
1. .33333333333 .33333333333 .33333333333    0. 0. 0.
K_POINTS {gamma}