[Pw_forum] highest occupied state

[stefano de gironcoli]

Dear ZARA (or NBSH, WBR, NN ?)

   as mentioned in some of the other answers you need to find the shift 
of the average electrostatic potential (the internal reference of the 
calculation) to the vacuum level.
   If your system is 0 dimensional then the assume_isolated option may 
be helpful.
   In particular the 'martyna-tuckerman' (or 'm-t' or 'mt') should work 
for you.
   check G.J. Martyna, and M.E. Tuckerman,"A reciprocal space based 
method for treating long range interactions in ab-initio and 
force-field-based calculation in clusters", J.Chem.Phys. 110, 2810 (1999).
   The zero of the potential is set to the vacuum level so the printed 
eigenvalue is directly what you want. Be careful if the HOMO becomes 
positive as this indicates the state is not bound and the correction has 
gone bananas.

   An alternative also working for different geometries is the 
electrostatic embedding implemented in the environ module and developed 
by Oliviero Andreussi and co-workers .
(check http://www.quantum-environment.org/)

best

stefano


On 26/07/2016 17:45, ZARA NBSH wrote:
> Dear users,
> I would like to calculate the highest occupied state energy of a 
> nano-structure with respect to the vacuum level.
>
> I took vacuum about 20A, if I increase the vacuum the total energy and 
> gap do not change but the highest occupied and the lowest occupied 
> states will be shifted up with a same amount.
> I can't understand the meaning of this energy shift,
> how can I calculate these energy respect to the vacuum level?
>
> I really appreciate your help in advance.
>
> WBR
> -NN
> Teran uni
>
>
>
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