[Wien] Freestanding Pb slab calculation

[Peter Blaha]

The procedure is ok. But you should accept the changes of sgroup !
It will move the origin so that you have inversion symmetry.

Am 08.09.2010 12:15, schrieb 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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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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