The ABINIT Users Mailing List ( CLOSED )

[Xavier Gonze <xavier.gonze@uclouvain.be>]

On 14 Feb 2009, at 16:10, Saniz Balderrama Rolando wrote:

> Dear all,
>
> I would like to ask what the band energies reference value is. I  
> guess a practical choice is the G=0 component of the Fourier  
> representation of the total Kohn-Sham potential (this is just the  
> average of the potential over the unit cell, which one can also  
> easily calculate from the grid values output setting prtpot==1). But  
> I don't know if this is what is done in Abinit.
>
> Thanks for your time!
>
> Rolando Saniz

Dear Rolando,

The G=0 of the Fourier representation of the local and Hartree  
potentials are set to zero
(actually both diverge), while the G=0 component of the XC potential  
is not set to zero.

Be careful : this G=0 component is actually undefined for physical  
reasons.
Indeed, think to the alignment of an average potential in the bulk and  
in vacuum :
the potential jump will depend on the strength of dipoles at the  
surface ! So, unlike
you know what is your surface, there is no unique way to align a bulk  
average potential
with the level of vacuum. In other word, the work function cannot be  
defined without
knowing the surface structure (so it might differ for different facets  
of a material).

Best regards,
Xavier

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