[Wien] Freestanding Pb slab calculation
Bartosz Slomski
bartosz.slomski at psi.ch
Thu Sep 9 16:23:49 CEST 2010
Dear Prof Blaha,
thank you very much for your advice. Now the structure looks as you
said. So after creating the struct file sgroup found the right symmetry....
I have now another question. The bandstructure of my slab looks now as
known from literature.
Now I would like to run a second SCF cycle with spin orbit coupling.
Since the system is a slab and non-magnetic I am not sure how to setup
the case.inso file.
My slab consists (for simplicity) of 2 independent and 3 total atoms in
the unit cell. Pb has two electrons in 6s and 2 electrons in 6p: how
should for this case the .inso look like?
----------top of file: case.inso----------
WFFIL
2 0 0 llmax,ipr,kpot
-10.0000 1.5000 Emin,Emax
0 0 0 h, k, l (direction of magnetism)
11 number of atoms with RLO
Peter Blaha wrote:
> The structure is still wrong. You should "see" it in xcrysden.
> The atoms must be at (0,0), (1/3,2/3) and (2/3,1/3) (A,B,C)
> and not at (1/3,1/3),...
>
> You cannot simply change the angle gamma from 60 to 120 without
> changing also
> the positions.
>
> I think it is pretty simple:
> Create the structure with octave (same way as you did before).
> Run sgroup and accept the structure.
>
> It gives a nice hexagonal structure.
>
>
>
> Am 08.09.2010 14:26, schrieb Bartosz Slomski:
>> After executing x sgroup with my initial Pbslab_34_34.struct I get
>> the warning: !!! Bravais lattice has changed.
>> sgroup found: 12 (C 2/m) [unique axis c] cell choice 2.
>>
>>
>> When I accept the structure of x sgroup, then the resulting structure
>> (Pb495_after_symmetry.struct) looks completely different from the
>> original one (Pbslab_34_34.struct)
>>
>> But, when I take the Au example and go through the initialization
>> then the message out of sgroup is just. symmetry group found sgroup
>> 164 (P -3m 1)
>>
>> So there must be something wrong in my initial structure that I dont
>> understand.
>>
>> When I create the slab with octave and load into structgen then
>> StructGen says about the lattice: nie_mam pojecia, which means, "dont
>> know the spacegroup", then I edit the
>> struct.file to lattice H and change gamma from 60° to 120°.
>> But then I get the error: incorrect space group symbol.
>>
>> Sorry for boreing you with all these questions and problems...perhabs
>> somebody can provide me the commands to produce a 111 surface?
>>
>> With best regards,
>>
>> Bartosz
>>
>>
>>
>> Peter Blaha wrote:
>>> 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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>>>
>>
>>
>>
>>
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>
--
Bartosz Slomski
------------------------------------------
Swiss Light Source, Paul Scherrer Institut
WSLA/205
CH-5232 Villigen PSI, Switzerland
Tel: +41 (0)56 310 5694
------------------------------------------
Physik-Institut, Universität Zürich
Winterthurerstr. 190
CH-8057 Zurich, Switzerland
Tel: +41 (0)44 635 5824
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