[Pw_forum] Hubbard U on surface

[Mike Marchywka]

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> Date: Tue, 22 Apr 2014 17:26:23 +0200
> From: Thomas.Brumme at impmc.upmc.fr
> To: pw_forum at pwscf.org
> Subject: Re: [Pw_forum] Hubbard U on surface
>
> 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?

well, if you define a metal as having infinite bulk conductivity and
then consider things like image charge does that explain anything? 
You could try replacing the metal with an idealized model for what you
think is causing the behavior I suppose. 


>
>
> 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.
>>
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>
> --
> 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
>
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