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[shaltaf@pcpm.ucl.ac.be]

Dear James,

The method that I know for calculationg work function, is simply by taking 
the difference between the vacuum level and the Fermi energy. 
The vacuum level is determined from the self-consistent, plane-averaged
potential, along the direction perpendicular to the surface, 
I wonder if this was what you were doing?

Riad 

Quoting James Johns <jej7x@xenon.cchem.berkeley.edu>:

> Ok, so I'm going partially off of the tutorials here, but I'm attempting
> 
> to approximate the workfunction of Magnesium(0001) surfaces.  I've 
> attatched a sample input file.  My problem is that despite all attempts
> to 
> better optimize the convergence critea based on nband, ecut, the kpt
> grid, 
> or anything, it's underestimating the workfunction by roughly a factor
> of 
> two.  I'm using the fermi level energy level from a 10 atom slab 
> calculation as the workfunction.  Is there something wrong with this? 
> When I do this for the Ag(111) surface, my estimation is roughly 
> 100-200meV higher than the experimental version.  The fact that it's
> only 
> slightly more ( and seems to converge based on typical paramters such as
> 
> size of vaccuum spacing etc), while on Mg it is severely less makes me
> 
> think that it's not something inherent in the LDA (or GGA)
> approximation. 
> Does anyone have any thoughts, or alterations to the input file to
> correct 
> for something I'm doing stupidly?
> Thanks a lot,
> --James Johns
> UC Berkeley
> Charles Harris group member
> 


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