[Pw_forum] how to judge movement of HOMO and LUMO

["José C. Conesa"]

Dear Rajdeep Banerjee,
In a recent paper of mine (http://dx.doi.org/10.1021/jp306160c) I used 
the van de Walle & Martin's scheme, later used by Pasquarello, to 
compute the band alignment at ZnO/TiO2(anatase) interfaces. The purely 
electrostatic (ionic + Hartree) potential was used as reference. At 
least the results agreed with experimental observations from Grätzel's 
group on certain DSSCs. What I would stress here is that one should pay 
attention also (as I did in that work) to the need of obtaining as 
reliable VB and CB positions as possible - which implies at least a good 
reproduction of the bandgap, a well known issue. A way to do so, without 
having to carry out rather expensive GW calculations, may be to use a 
PBE0 hybrid functional with the fraction of HF exchange tuned to the 
optical dielectric constant (a suggestion by Lucia Reining's group); see 
the mentioned paper as well as 
http://dx.doi.org/10.1016/j.cattod.2012.08.039 for details and references.
Good luck,
José Carlos

El 04/06/2014 14:10, Sclauzero Gabriele escribió:
> Dear Rajdeep Banerjee,
>
>      I think what is used as reference potential is the bare ionic potential + Hartree potential (V_bare + V_H). I kind of justification for that is given in this older paper by van de Walle & Martin (http://journals.aps.org/prb/pdf/10.1103/PhysRevB.35.8154) about band lineups at heterointerfaces.
>
> I agree with Nicola that the problem is subtle, given that a pure bulk calculation for an infinite solid cannot provide absolute energy levels.
> Hopefully someone with clearer ideas than me will be able to suggest alternative solutions.
>
> Best,
>
> GS
>
>
> Dear Sclauzero  Gabriele,
>                                      I looked at the paper you suggested (http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.101.046405) where it was said that the "common reference level (phi) " is calculated as the "cell average of the local potential originating from the ionic pseudopotentials" which I guess can be calculated from the pseudopotentials used. Can you suggest any functional form for this calculation of phi ? or indicate how to generate it from the pseudopotentials used?
>
> As far as I understand, after defining phi, the CBM and VBM can be described by:
>
>
> CBM = Ec - phi
> VBM = Ev - phi
>
> where Ec and Ev are LUMO and HOMO respectively.
>
> Thank you very much for all the help.
>
> Rajdeep Banerjee
> JNCASR,
> Bangalore, India
>
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>
> Dr. Gabriele Sclauzero
> Materials Theory - ETHZ
> ETH Zurich, HIT G 43.2
> Wolfgang-Pauli-Str. 27
> 8093 Zürich, Switzerland
>
> Phone +41 44 633 94 10
> Fax +41 44 633 14 59
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>
>
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-- 
José C. Conesa
Director
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Cantoblanco
28049 Madrid - Spain
Tel. +34-915854766