[Pw_forum] how to judge movement of HOMO and LUMO

[Giuseppe Mattioli]

Dear Rajdeep Banerjee,
There is also a "dirty trick" that can be used (with some success, at least in my experience, and if you do not want to be very subtle...:-)) to align 
the eigenvalues. If your lattice is not too tight, you can try to insert a He atom inside the largest interstitial site. If you put the He always in 
the same site, and provided that it does not mix too much with the lattice charge density (you can check it with projwfc.x), then you can use the 1s 
He level to realign the eigenvalues of different systems.
HTH

Giuseppe

On Wednesday 04 June 2014 14:10:55 Sclauzero Gabriele wrote:
> 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
> gabriele.sclauzero at mat.ethz.ch<mailto:gabriele.sclauzero at mat.ethz.ch>
> www.theory.mat.ethz.ch
> 
> 
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   Giuseppe Mattioli                            
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