[Pw_forum] what is the relevance between the Kohn-Sham Orbital isosurface and real molecular orbitals?

[yavar pour azar]

Dear Professor  Seitsonen


Thanks for your consideration
and sorry so late answer

Bests.

Yavar




On Sun, Dec 30, 2012 at 7:50 AM, Ari P Seitsonen <Ari.P.Seitsonen at iki.fi>wrote:

>
> Dear Yavar Taghipour Azar,
>
>   From what I know, only the energy eigenvalue HOMO should have a physical
> meaning - the ionisation energy - but also it would naturally require the
> usage of the exact exchange-correlation functional. All the rest relies on
> the empirism, that they seem to correspond quite reasonably the
> qualitative, often also quantitative results from the experiments and
> chemical picture/intuition, or the more accurate theoretical methods
> (quantum chemical approach like coupled-cluster methods, many-body methods
> like GW and Bethe-Salpeter equations). So there is no theoretical
> foundation for the usage of the Kohn-Sham orbitals and eigenvalues, just
> the overall general agreement and convenience (which can sometimes be read
> also as "lazyness" ;).
>
>   Hopefully this clarifies your confusion at least partially. The
> textbooks should discuss this also this more "practical" aspect, strange if
> they don't. I don't remember when/if this topic has been discussed already
> before (mailing list/FAQ), sorry.
>
>     Greetings from Zurich,
>
>        apsi
>
> -=*=-=*=-=*=-=*=-=*=-=*=-=*=-=***=-=*=-=*=-=*=-=*=-=*=-=*=-=*=**
> -=*=-=*=-=*=-=*=-
>   Ari P Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
>   Physikalisch-Chemisches Institut der Universitaet Zuerich
>   Tel: +41 44 63 54 497  /  Mobile: +41 79 71 90 935
>
>
>
> On Sun, 30 Dec 2012, Yavar Taghipour Azar wrote:
>
>
>>  Dear QE user
>>
>> As mentioned in some text books (for eample, A Chemist’s Guide to Density
>> Functional Theory);
>> The orbitals satisfying Kohn-Sham equation  have no physical significance
>> and their only connection
>> to the real world is that the sum of their squares add up to the exact
>> density.
>>
>> by considering this, I cant understand physical relevance of isosurfaces
>> which plotted in pw postprocess and
>> the real molecular orbitals (HOMO, LUMO, LUMO+1................).
>>
>> thanks in advance
>>
>> Yavar Taghipour Azar
>>
>> Condensed Matter Section, AEOI
>>
>> Tehran, Iran
>>
>
>
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