[gpaw-users] How can the vacuum potential be found out

[Ask Hjorth Larsen]

Hi

On Mon, 6 Feb 2012, Georg Kastlunger wrote:

> Which boundary do you mean?
> Is it the value at one certain point in the cell or an average of an
> interface between unit cells?
>
> Best regards,
> Georg

The potential is zero at all the non-periodic cell boundaries.  This means 
one cannot shift the potential arbitrarily - it is unique, and so are the 
eigenvalues.

Each eigenvalue equals the derivative of the total energy with respect to 
the occupation of the corresponding state (keeping wavefunctions and 
density constant).

(The same is not true if the cell is fully periodic; then I'm not sure 
what determines the potential and eigenvalues)

Regards
Ask