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[Pawel Scharoch <Pawel.Scharoch@pwr.wroc.pl>]

       Dear James,

    just one remark: calculations of any quantity with the use of 
 a metallic slab models require convergence tests with respect to the 
 number of monolayers, because of the quantum size effect (QSE)
 (see e.g.:   Kiejna A. et al. Quantum-size effect in thin Al(110) slabs, 
 Surf Sci 432 (1-2): 54-60 Jul 9 1999). Of course I am not sure 
 whether this effect is responsible for the discrepancy you get. 

 With best regards, 



----- Oryginalna wiadomość -----
Od: James Johns <jej7x@xenon.cchem.berkeley.edu>
Data: Niedziela, Kwiecień 22, 2007 6:49 am
Temat: [abinit-forum] Mg workfunction
Do: forum@abinit.org

> 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
> 
>