[Pw_forum] Hubbard U on surface

[Thomas Brumme]

Hi,

I think that this is not universal since

- U in general depends on the structure of your system. The structure is 
changed due to the interaction with the surface.
Thus, I think that there should be a difference between, e.g., 
adsorption on Au(111) and Cu(111) since in the former case
you might have physisorption while in the latter it is probably 
chemisorption

- also an extension to other metal center is not straightforward. This 
increase in U might be happening for Fe but what
is with Cu, or Co?


On the other hand, if you're using the method of Cococcioni et al., U is 
calculated by changing the occupation of the iron
d-orbitals. This occupation however depends on the system and it is 
definitely different for the molecule on the surface.
And it crucially depends on the molecule, the metal center, the surface, 
and so on...

For example, some kind of backbonding can occur. The iron donates 
electrons to the ligand. However, if you adsorb
the molecule the ligand forms a bond with the metal surfaces (even if it 
might be weak in case of Au(111) ), and the metal
surfaces in turn donates some charge to the iron, effectively increasing 
the occupation compare to the vacuum case.
This might change U...

Thus, I think it is not universal, but I'm not entirely sure, so please 
correct me if I'm wrong.

Thomas

On 04/22/2014 04:21 PM, 庞瑞 wrote:
> Dear all:
>     I have calculated Hubbard U of transition metal coordinations like
> Fe(porphyrin) with linear response method.I find the Hubbard U usually is
> larger when the molecule adsorped on metal surface than it is in vaccum. Is
> this universal? Is there any explain available?
>     Thanks.
>   
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

-- 
Dr. rer. nat. Thomas Brumme
Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie
Sorbonne Universités - UPMC Univ Paris 06
4 Place Jussieu
75005 Paris

Tel:  +33 (0) 1 442 77204

email: Thomas.Brumme at impmc.upmc.fr