[Wien] Freestanding Pb slab calculation

[Bartosz Slomski]

Dear Mr Blaha,

indeed my structure does not represent a surface along [111].
I made a mistake using structgen/octave. Instead of using 
makeconventional one should use "makeprimitive"
Afterwards one has to change in StructGen the gamma angle to 120° and 
select lattice type H.

The final structure (Pb_slab_34_34.struct) has the stacking of A-B-C but 
still differs slightly from the Au example.
In the Au example there is vacuum between the 12th layer and the 13th 
layer, or are the layers 13..24 just the repeated unit cell of layer 1..12?

During initialization of the Pb_slab I get the warning: you must move 
the origin.

Perhabs the procedure to generate a surface along [111] is still wrong.

Thanks and best regards.


Peter Blaha wrote:
> Have you looked how the generated structure looks like ? (xcrysden)
>
> It is not correct.
>
> I'm not the expert with structgen and thus cannot tell you, where the 
> error is.
>
> In any case, an fcc-111 surface is very easy (although one cannot use
> directly the supercell program).
>
> Have a look into example_struct_files/Gold_23l.struct
> This is an fcc 111 structure. All you need to do is to adjust the
> lattice parameters and eventually delete some of the atoms (if you 
> want just
> 6 layers instead of 23).
>
> Remember the stacking: A-B-C .... !
>
> PS. In general it is NOT a good idea to neglect 
> warnings/errors/suggestions
> from nn or sgroup, unless "you know why you are doing it".
>
> A 6-layer slab has inversion symmetry and only 6 atoms/cell !
> It runs in a couple of minutes, not 19 h.
>
>

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