[Pw_forum] band energies

[Helen]

Dear Nicola,
Thank you very much for your reply,
Helen
----- Original Message ----- 
From: "Nicola Marzari" <marzari at MIT.EDU>
To: "PWSCF Forum" <pw_forum at pwscf.org>
Sent: Monday, March 31, 2008 1:15 PM
Subject: Re: [Pw_forum] band energies


>
>
>
> Dear Helen,
>
> there are several ways to look at this - most thorough discussion would
> be Caspar Fall PhD thesis at EPFL (www.epfl.ch) - it's available on the
> web. Also, for a recent review, citing most of the relevant literature,
> you could look at http://arxiv.org/abs/0801.1077 . The papers
> by Baldereschi/Baroni/Resta/Peressi from the late '80s onwards on
> homo and heterosemiconductor junctions contain the original discussion
> of these issues.
>
> In short - you can refer the homo of your bulk semiconductor to another
> property that is easy to transfer across non-bulk environment - often
> the average value of the Hartree or of the Kohn-Sham potentials. Suppose
> the HOMO were 3.5 eV above the Hartree bulk average.
>
> Then, in a slab calculation, you can find out what is the average
> Hartree well inside the slab (where it is bulk-like), and well outside
> the slab, what it reaches the vacuum level. Suppose this difference
> is 5eV. Then, the HOMO is 1.5eV below the vacuum level - i.e. it takes
> 1.5eV to bring the top valence electron well outside the solid (across
> the surface used in your slab calculation - these quantities are surface
> dependent).
>
> nicola
>
>
>
> Helen wrote:
>> Hello,
>> So far I've been calculating bandgaps and so have been using the
>> differences in band-energies, now I want to compare the absolute value
>> of the HOMO in semiconductors with experimental workfunctions. How can I
>> know what the absolute zero value of the bandenergies is? Is there any
>> meaning to the absolute values given in the output file or are only the
>> band energy differences relevant?
>> Thanks for your help,
>> Dr. Helen Eisenberg,
>> Fritz Haber Center, Hebrew University.
>>
>>
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>
> -- 
> ---------------------------------------------------------------------
> Prof Nicola Marzari   Department of Materials Science and Engineering
> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
> tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
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