[Wien] Change of structure symmetry

[Laurence Marks]

I meant "correct" when the cell is C11m, which is better for Wien.

On Wed, Oct 12, 2016 at 10:50 AM, Laurence Marks <L-marks at northwestern.edu>
wrote:

> My two cents worth. If you look at, for instance, https://en.
> wikipedia.org/wiki/List_of_space_groups, Cm #8 is a monoclinic spacegroup
> which (in the B11m setting) has beta .ne. 90. It is "correct" to have gamma
> .ne. 90 for the standard convention. However, this is inconvenient and it
> would be nice if sgroup made an exception for Wien.
>
> On Wed, Oct 12, 2016 at 10:14 AM, Peter Blaha <
> pblaha at theochem.tuwien.ac.at> wrote:
>
>> ===================================================================
>>
>> The structure that you have attached does NOT have Cmm2 as space group
>> symmetry, but only Cm, which is the one that sgroup correctly finds. The
>> mirror plane of the Cm group is perpendicular to the original a axis, and
>> in the standard description of Cm it should be perpendicular to the b
>> axis.
>> That is the reason why it interchanges the axes, to make the old a axis
>> become
>> the new b one. It is however true that it could have however kept the
>> original
>> unit cell metrics, with the axes interchanged. The program indeed does not
>> seem to have any particular criterion to optimize the choice of the unit
>> cell within the standard description of the space group, and as Peter
>> Blaha
>> says there are many possible choices for monoclinic space groups. The
>> program just chooses one, the reason being that your structure is
>> monoclinic
>> with Cm symmetry and not Cmm2.
>>
>> J. Manuel Perez-Mato
>> Fac. Ciencia y Tecnologia,
>> Universidad del Pais Vasco, UPV
>> 48080 BILBAO,
>> Spain
>> ***************************************************
>>
>>
>> On 10/12/2016 04:50 AM, delamora wrote:
>> > I want to see how Cu interacts with the TiO2 surface, so I construct
>> > with 'supercell' an enlarged cell, with
>> > SG 35 (C m m 2)
>> > then I attach Cu and O on the surface in a way that I break the symmetry
>> > in the b direction
>> > The cell is orthorhombic
>> >
>> > CXY LATTICE,NONEQUIV.ATOMS: 21
>> > MODE OF CALC=RELA unit=bohr
>> >  11.187184 23.838706 23.838290 90.0 90.0 90.0
>> >
>> > if I run initialize calculation and then sgroup the new cell changes to
>> >
>> > CXZ LATTICE,NONEQUIV.ATOMS: 28 8 Cm
>> > MODE OF CALC=RELA unit=bohr
>> >  23.838706 33.712727 11.187184 90.0 90.0 135.000500
>> >
>> > which is correct, but it is no longer orthogonal which is awkward, one
>> > angle changes from
>> > 90 to 135.0005
>> > also the a, b, c => c, a, b
>> >
>> > Also I cannot see the structure with XCrySDen, unless I change the
>> > 135.0005 angle by little.
>> >
>> > With the new structure and the old one I managed to make a new
>> > TiO2.struct with orthorhombic and can be seen with XCrySDen
>> >
>> > It would be nice that sgroup would generate a structure with the
>> > orthorhombic symmetry
>> >
>> >               Saludos
>> >
>> >                       Pablo de la Mora
>> >
>> >
>> >
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>>
>> --
>>
>>                                        P.Blaha
>> ------------------------------------------------------------
>> --------------
>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
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>
>
>
> --
> Professor Laurence Marks
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought", Albert Szent-Gyorgi
> www.numis.northwestern.edu ; Corrosion in 4D:
> MURI4D.numis.northwestern.edu
> Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
> Co-Editor, Acta Cryst A
>



-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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