[Wien] Obtaining the Reference Energy for Calculated Band Structure

[Craig Plaisance]

Thank you for the response.  It seems to me, though, that one could 
obtain the potential at a position (r) inside an infinite lattice 
relative to the vacuum (excluding contributions from surface charge and 
the electrostatic double-layer since the dopant atom is also inside the 
surface) by integrating over the entire lattice (in reality only a few 
neighboring unit cells since the contributions to the potential from 
unit cells far away from r vanish due to charge neutrality) the 
contribution from each point (r').  The integrand is simply p(r')/|r-r'| 
where p(r') is the total charge density at r'.  The exchange-correlation 
potential at r is then subtracted from the integral and the result is 
the potential at r relative to vacuum.

Peter Blaha wrote:

>Hi,
>
>A "bulk" calculation is for an "infinite" solid and thus even at infinity
>there are atoms. So there is no chance to obtain what you are looking for
>from the bulk.
>
>The only way to do this is by a simulation of a "surface-slab" with some
>(as thick as possible) vacuum between the slabs (which should also be as
>thick as possible).
>Realistically, this depends on your sample, but maybe even 7 layers of
>bulk will do it, seperated by 30 bohr of vaccum. The potential in the
>middle of the vacuum (printed in the scf file) could serve as your
>"reference potential" at "infinity".
>
>  
>
>>I know that Wien references all calculated energy levels to the average
>>lattice potential, but is there a way that I can obtain this average lattice
>>potential relative to the lattice continuum threshhold (the potential at
>>infinite distance from the crystal plus the surface potential barrier).  I am
>>probably not explaining this well, so I will elaborate by giving an example of
>>why I want this information.  Suppose I have a lattice for which I have
>>calculated the band structure using Wien and I want to compare this
>>bandstructure to the atomic energy levels of a dopant atom (which are
>>calculated relative to the potential at infinite distance from the atom using
>>a package such as Gaussian).  In order to make this comparison, I need to
>>shift the lattice energy levels by an appropriate amount so that they have the
>>same reference as the atomic levels.  How do I get the value for the energy
>>shift?  Thanks.
>>
>>Craig Plaisance
>>Louisiana State University
>>Baton Rouge, LA
>>
>>_______________________________________________
>>Wien mailing list
>>Wien at zeus.theochem.tuwien.ac.at
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>>
>>    
>>
>
>
>                                      P.Blaha
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>Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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