[Pw_forum] Electron affinity calculation

[Stefano Baroni]

On Jan 31, 2007, at 3:50 PM, Alexander Shaposhnikov wrote:

>
> I have tried several slab models and the first conduction band
> is still meaningless, i.e. much higher than it should be in real  
> crystall.

the absolute value of the energy levels are of course as meaningless  
as they are for a bulk calculation, and for the same reason: the  
average electrostatic potential of an infinite solid is ill defined  
(periodically repeated slabs do constitute an infinite, periodic,  
system). What you ought to look after is the position of individual  
energy levels *with respect to the value of the potential in the  
vacuum region*.

> I have not tried to optimize the structures though.
>
> I guess, i have to
> 1. Optimize the structure.

fine

> 2. Remove some electrons from the system, hoping to create surface  
> charge.

I think that the value of the lumo energy with respect to the vacuum  
potential should be a fair estimate of the electron affinity you are  
looking for.

S.


---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
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