I do not find much sense in the data you sent ???
When you want to calculate the O2 binding energies, the RMTs and RKmax
values of O and O2 need to be IDENTICAL. And yes, break a bit the
symmetry (use slightly different a,b,c) to get the lowest energy for
atoms according to Hunds rule.
---------------------------------------------
If you want to calculate cohesive/formation energies, you must use
identical RMTs and "equivalent RKmax".
So for a Me_xO_y compound, you would first optimize the structure.
Optimization in genergal involves lattice parameter (at least voluem)
AND internal positions (forces).
Then you need to calculate the O2 energy and the Me (typical this is the
metallic phase of this element, like bcc Fe or fcc Al,...).
To do so, you need to use a small RMT for O2 because of the samll bond
length. Optimize the O2-distance eg. with 1 k-point and RMT 1.2 and
RKMAX 5.5.
Then repeat your Me-O compound (in the relaxed minimum structure) with
this same O-RMT (1.2) and also RKmax=5.5 (but a good k-mesh).
Finally do the Me phase (with the same Me-RMT as in your compound) and a
RKmax= 5.5 / 1.2 * RMT(Me) !!!!!
Form the energy difference to find the cohesive energy.
Now repeat the O2, MeO and Me calculations, where you increase RKmax
from 5.5 to eg. 6.0. Form again the difference. If it is stable, you are
done, if not, increase RKMax again (6.6 or 7, depends also on your Me
and compound) until you get a stable cohesive energy.
PS: When increasing RKmax, check the forces on the atoms if they remain
small (usually they do unless you started much too small).
Am 23.04.2018 um 12:14 schrieb chin Sabsu:
Dear Sir,
I am thankful for the confirmation of the state of O2 molecule.
I am tried to reproduce some results for oxygen deficient system but I
see from my data that my system is not stable.
I started from the given lattice parameters, exact functionals,(GGA, as
suggested in the paper) rmt k-mesh etc.
The authors did not mention anything about how they have calculated the
formation energy and atomization energy. In my previous post your reply
with some notes, I followed the same data to simulate ground state
energy of O2 and O but still am not getting the reasonable results.
As I used data for O2 from FAQ and also tried according to the
information given in the literature paper.
I see there should not be any issue in calculating the O2 energy.
My doubt is somewhere in the calculation of O (-sp) with below data:
Title
F LATTICE,NONEQUIV.ATOMS: 1
MODE OF CALC=RELA unit=bohr
28.345900 28.345900 28.345900 90.000000 90.000000 90.000000
ATOM 1: X=0.00000000 Y=0.00000000 Z=0.00000000
MULT= 1 ISPLIT= 2
O NPT= 781 R0=0.00010000 RMT= 1.65000 Z: 8.000
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
0.0000000 0.0000000 1.0000000
48 NUMBER OF SYMMETRY OPERATIONS
and
O
He 3
2,-1,1.0 N
2,-1,1.0 N
2, 1,1.0 N
2, 1,1.0 N
2,-2,2.0 N
2,-2,0.0 N
****
**** END of input (instgen_lapw)
below are data from O2 and O-atom with GGA
O_atom_rmt_1.75_rkmax_7 -149.86322972
O_atom_rmt_1.1_rmkax_5.5 -150.0869798
O2_mol_bondlength_1.21_rkmax_5.5 -300.1077091
[O2_mol_1.21]\2 -150.05385455
O3_mol_1.21 -450.16156365
O2_mol_bondlength_1.219_rkmax_4.6 -299.95534741
[O2_mol_1.219]\2 -149.977673705
O3_mol_1.219 -449.933021115
In his previous post in response of my query, Prof. Alay advice about
calculating the ground state energy of O-atom by considering O atom cell
as orthorhombic to avoid any issue occurring from the occupancy of
P-states of O-atom. His statement is quoted below:
"Computing the atomic energies of atoms like N and P in an FCC cell is
ok, however for O atom the high symmetry of the FCC cell results in 1/3
occupancies (for the 4th p electron of O) in the spin down case. Only using
a lower symmetry cell (orthorhombic) for O atom eliminates this issue."
Could you please advise me whether my above data looks good or not.
If I have to follow the suggestion advanced by Prof. Alay, then how to
make an Orthorhombic cell for O-atom?
I have done three calculations for three materials but I am not getting
the atomization and formation energy of O2 while the author reported
similar statements in his papers.
Please help me to simulate the ground state energy of O2 and O taking
care of occupancy of P orbitals.
Please let me know what additional information I can provide.
thank you very much for a big help.
Chin S.
On Monday, 23 April, 2018, 10:32:22 AM IST, Peter Blaha
<pbl...@theochem.tuwien.ac.at> wrote:
This is the configuration for a spin-polarized O atom.
And yes, this starting configuration will lead to the triplet state of
O2 (when you perform spin-polarized calculations.)
Am 22.04.2018 um 08:16 schrieb chin Sabsu:
> Dear Users,
>
>
> Could you please advice me whether below *.inst form O2 in triplet
> state? three e- in dn and one e- in up state?
>
>
> O
> He 3
> 2,-1,1.0 N
> 2,-1,1.0 N
> 2, 1,1.0 N
> 2, 1,1.0 N
> 2,-2,2.0 N
> 2,-2,0.0 N
> ****
> **** END of input (instgen_lapw)
>
>
> Thanks and best regards,
>
> Chin S.
>
>
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Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
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