[Wien] Testing convergence with size for a surface

[Peter Blaha]

I only know from literature a similar problem when calculating the surface 
energy  (E-slab - n*E_bulk). This suffers from the same numerical 
uncertainty and if I remember correctly, people use an extrapolation 
procedure using 2 or 3 different slab thicknesses to extrapolate to 
"infinite" thickness WITHOUT using the bulk energy.
Please check the exact procedure in literature.
 
> I want to check the convergence of a surface calculation versus the slab
> thickness. The obvious way is to calculate the difference
>        E_diff = E_slab2 - E_slab1 - n*E_bulk
> where slab2 has n more layers than slab1. Unfortunately there is a problem
> with this. For a conventional small cell bulk calculation, RKMAX is rounded
> down (exact size depending upon the k-vector), so it's not completely obvious
> what the RKMAX for the slabs should be and this can make a big difference. I
> tried plotting E_bulk versus RKMAX and interpolating, but I don't think I
> believe the results.
> 
> Has anyone worked through this in detail to find a viable method?
> 
> Note: if you have an old email address for me, please note that "nwu" has
> been changed to "northwestern".
> -----------------------------------------------
> Laurence Marks
> Department of Materials Science and Engineering
> MSE Rm 2036 Cook Hall
> 2220 N Campus Drive
> Northwestern University
> Evanston, IL 60201, USA
> Tel: (847) 491-3996 Fax: (847) 491-7820
> email: L-marks at northwestern dot edu
> http://www.numis.northwestern.edu
> -----------------------------------------------
> 
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> 


                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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