Different oxidation states

[kambiz]

Hi dear all,

Is there a way to differentiate between Co+2 and Co+3 in Co3O4? Co3O4 is a mixture of Co+2 and Co+3. I want to replace some atoms with each other. I really appreciate any help

Cheers

[Danny]

Co+2 and Co+3 are chemical concepts, in reality (and in VASP calculations) you only have Co atoms, the +2 or +3 results from the system.
As a direct concequence: you will not be able to switch Co+2 by Co+3 or vice versa.

Which of the Co atoms is +2 or +3 you can deduce from the geometry(cf: lewis structures from molecules). You can also try to figure out the charge of the atoms using a Hirshfeld-I approach(something I'm currently working on). This however will not give you the valences, but you should be able to see the difference between +2 and +3 atoms.

Danny

[kambiz]

Hi Danny,

Thanks for you reply, However, we can model both neutral O2 and O2- (superoxide) by adding a charge in VASP. So I think that there is a way that we do the same thing for Co in Co3O4. What do you think?

Cheers
Kambiz

[vistawanted]

Once you check the ICSD, you can distinguish 2+ and 3+ Co ions.:
Unit Cell 8.065 8.065 8.065 90. 90. 90.
Vol 524.58
Z 8
Space Group F d -3 m S
SG Number 227
Cryst Sys cubic
Pearson cF56
Atom # OX SITE x y z
Co 1 +2 8 a 0 0 0
Co 2 +3 16 d 0.625 0.625 0.625
O 1 -2 32 e 0.388 0.388 0.388

[vistawanted]

Furthermore, I do not think Co ions exist exactly 2+ and 3+, Lewis or Mulliken charge population may tell you more detailed information. After all, Co ion at (5/8, 5/8, 5/8) should have less charge than (0,0,0) one.

[Danny]

[quote="kambiz"]Hi Danny,

Thanks for you reply, However, we can model both neutral O2 and O2- (superoxide) by adding a charge in VASP. So I think that there is a way that we do the same thing for Co in Co3O4. What do you think?

Cheers
Kambiz[/quote]full system[/b]...but not of single atoms.

@Vistawanted: exactly. Population analysis will tell you a bit more, and depending on the setup(e.g. mulliken vs Hirshfeld(-I) vs Bader) the chemical information will be different. It will, however, not give you the oxidation as + or - some integer which chemists are so fond of. Co+2 and Co+3 do not exist as entities(in a molecule/solid), you only have Co.

Danny

[kambiz]

Cheers Guys

Thanks