[Wien] quasiparticles

[Ashok Kumar Verma]

dear Prof.,
       Now days I am not recieving any wien-users mail. Is there any
problem.
with best regards
ASHOK



On Wed, 8 Oct 2003, Stefaan Cottenier wrote:

> > Could somebody explain or point out further reading, why such a comparison
> > is obviously valid?
>
>
> I'm not at all an expert in "DFT philosophy", but this is my understanding
> of the problem:
>
> The Kohn-Sham scheme guarantees you that it yields the correct total energy
> and the correct density (if you would use the exact XC-functional). On the
> way to these 2 objects, the Kohn-Shame scheme introduces some wave-function
> like objects of which the scheme itself provides no physical interpretation.
> One should just throw away these wave functions once you have obtained E_tot
> and the density.
>
> Of course, we want to know more than just E_tot and the charge density. We
> want to know e.g. the fermi energy, or a magnetic moment. DFT tells that
> this information is contained in the charge density (which we have just
> calculated), but it doesn't tell us how the functional for the fermi energy
> or the magnetic moment would look like -- so that doesn't help us. Now comes
> the magic: close your eyes and do as if those wave-function like things are
> true single electron wave functions, and calculate the expectation value for
> these wave functions using the normal magnetic moment operator (which we
> know, in contrast to the corresponding functional). It's absolutely illegal
> and unjustified, but comparison with experiment shows that it works... So
> everybody does it.
>
> Your question was *why* this works. I don't know whether this is known or
> not, I suppose it isn't. I remember something is written about this in the
> book of C. Pisani (QM ab initio calc. of the properties of cryst. mat.,
> Springer, 1996), but I cannot find the relevant page right away. For sure
> there must be more and/or recent discussions on this. I'll be glad to get
> references from other users as well...
>
> Stefaan
>
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