[Pw_forum] About valence bands maximum

[lan haiping]

Thank you, Guido.
Regards,
H.P

On 4/19/07, roma <roma at srmp.saclay.cea.fr> wrote:
>
> Dear Ian Haiping,
>
> it is true that seldom papers about defects discuss this point, and I am
> probably guilty of this too. My understanding is that your expression
> for the valence band top of the defect is correct, but then it depends
> on how you use it. What has been omitted according to the person that
> told you this?
> The crucial quantity is [<V(D,q)> -<V(0)>] (let us call it
> DeltaV(D,q) ). Long ago I did a small program to calculate the so called
> macroscopic average of the potential (Balderesci, Baroni,Resta, PRL v61,
> p734, 1988) in the supercell: it was ok for a defect in a simple metal
> (I could find the "bulklike" region) but for the system I was interested
> in, SiO2, the oscillations of the macroscopic average along the
> supercell made it useless. Supercell too small? Problems due to the
> symmetry of my supercell? I adopted a different strategy, I determined
> the energy shift that maximises the overlap (or minimises the square
> differences) of the density of states of the defected and perfect
> crystal. This shift is for me DeltaV(D,q).
> This, according to my experience, can be unambiguosly determined as long
> as the relaxations are good (and k-point sampling is sufficient).
> Then another question is to which extent the DeltaV term corrects for
> the image interaction of charged defects, on which I would appreciate
> also the feedback from others on the list.
> Best regards,
>
> Guido
>
>
>
>
>
> On thursday April 12 Ian Haiping wrote:
>
> >    I want to determin  the transition enery of a defect level.  It is
> >important to align the valence bands maximum of different systems under
> >investigation. Many works  has claimed valence bands maximum alignments
> >were performed but no technique details are given.
>
>
> >For my understanding,
>
>
> >I thougt the valence bands maxium of charge defect systems could be
> >determined by aligning its average potential
>
>
> >to pure perfect system's potential, e.g  \epsilon_{VBM}.(Defects,q) =
> >\epsilon_{VBM}(0) + [<V(D,q)> -<V(0)>].   But some person told me  such
> >expression has omitted something.    So it really confused me much. As
> >far as i know,  the potential of system could be only determined  to
> >some constant . i thought the alignment of average potentials of two
> >systems could take into account this arbitrariness.. I am not very
> >certain about this  VBM alignment right now   Would you give me some
> >comments and clarify my understanding ?
>
>
> >
> --
> Guido Roma <roma${at}cea.fr> -- CEA-Saclay - DEN/DMN/SRMP Bat.520/13
> Phone: [+33]-1-69081857 -- Fax: ...6867 -- Mobile: [+33]-6-20069085
>
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-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
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