[CPMD-list] About getting surface energy in CPMD

[Ari P Seitsonen]

Dear Wone Keun Han and Hong Won Keon,

On Tue, 15 Mar 2005, Wone Keun Han wrote:

> Dear W. K. Hong,
>
> One of the ways to get surface energy is
>
> E_surf = (E_slab(N) -N*E_bulk)/2, where N is the number of layers of your
> slab.
>
>
> I happened to calculate Pt surfaces these days using other program.
>
> I am pretty much interested in your work.
>
> Can you give your surface energy to compare with mine?
>
> And which pseudopotential are you using?
>

As mentioned by Wone Keun Han this method above is one of the methods;
most likely it's the easiest one. But please be aware that it is very
sensitive to errors in the k points sampling, less so for the cut-off
energy etc. More accurate estimates can be obtained if one calculates
slabs with different thicknesses and uses extrapolation etc. Also please
notice that you'll get somewhat incorrect results if you relax the atoms
only at one surface, since both sides of the slab are no longer identical
and thus the factor "1/2" is not valid. One could e.g. first calculate the
surface energy of the unrelaxed surface with different number of substrate
atoms and then the corresponding numbers with the relaxation of one
surface only. Or, like usually done, one relaxes the atoms on both
surfaces simultaneously.

   What was probably confusing Hong Won Keon is the notation "chemical
potential of the species in bulk"; this is, like written in the answer of
Wone Keun Han, estimated with the total energy (extrapolated to zero
broadening of the occupation numbers) of the bulk material, NOT the value
of chemical potential (~= Fermi energy) reported by CPMD.

     Greetings again from Paris (after a meeting in Les Arcs/Savoie),

        apsi

-- 
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   Ari P Seitsonen  /  Ari.P.Seitsonen at iki.fi  /  http://www.iki.fi/~apsi/