In which orbital is an excess electron placed in charged system?

[Matt W]

Hi Fernan,

> I would like to know how CP2k models an excess electron placed in a 
> neutral system with N electrons by writing CHARGE -1.0 in the section 
> CP2K_INPUT / FORCE_EVAL / DFT. Is this excess electron placed in the LUMO 
> N-orbital?
>
> this isn't really how things work. The KS equations are solved, then 
filled up obeying the Aufbau principle. If the excess charge doesn't 
disturb the existing charge density, then it would be in an orbital very 
similar to the previous LUMO.
 

> In addition, does cp2k correct the eigenvalues to the vacuum level? Or do 
> they need to be corrected after the simulation is completed? Is there any 
> reference?
>

this depends on you boundary conditions (POISSON solver). In a periodic 
calculation there is no vacuum, or anything outside the system, and the 
energy levels are arbitrary. In a surface or molecular system (without 
dipole) the WAVELET solver will give the levels relative to zero.

Matt 

>
> Best regards,
>  - Fernan Saiz, PhD
> Department of chemistry
> Imperial College London
>
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