[Wien] sgroup question

Wed Oct 17 14:22:14 CEST 2012

Sorry Manu, but I think in WIEN2k it is "more comlicated":

It is of course true that WYCKPOS offers just two choices for SG 12:

C2/m:unique axis b   with a centering of (1/2,1/2,0)
C2/m:unique axis c                       (0,1/2,1/2)

However, WIEN2k  requires for monoclinic centered lattices a centering of (1/2,0,1/2)
(we call it "CXZ-lattice") and the monoclinic angle must be gamma. Thus NONE of the
settings of WYCKPOS is compatible with WIEN2k.

Instead, when I programmed this a long time ago, my Int. Tables had just two settings
for SG 12, which are called:

B2/m:unique axis c   with a centering of (1/2,0,1/2) (or a "proper name of" B112/m)
and
C2/m:unique axis b   with a centering of (1/2,1/2,0)  (or C12/m1) (this is the first C2/m of WYCKPOS)

I was "lazy" and implemented only the first choice and thus WIEN2k supports so far only
B112/m with xz-centering and angle gamma, or in short: B2/m

Conversion can be made with your nice utility   SETSTRU  as was indicated by Gavin Abo
(which also works in case somebody has the I2/m setting of this SG)
or "by hand" when interchanging all y <--> z pos.parameters,angles,latt.params.

Best regards
Peter

Am 17.10.2012 13:52, schrieb J. Manuel Perez-Mato:
> As far as I as I remember, sgroup finds and gives the standard space group
> corresponding to the structure:
>
> In monoclinic systems there are two alternative standards in the
> International Tables: unique axis along b o unique axis along c. For
> instance, the Bilbao server normally uses the first one, but in some of
> its programs like WYCKPOS, it offers you the two possible standards. It
> seems that sgroup uses the second possible standard "unique axis c", and
> in your case it is only proposing a change to this standard setting.
>
> I do not think there is any error in the output of sgroup and in principle
> nothing should be changed, because when announcing the space group:
> "(C2/m) unique axis c", the "(C2/m)" here is only used as synonym of space
> group  Number 12, and it does not mean that the centering translation is a
> "C" centering, i.e. (1/2 1/2 0), which is impossible if the c-axis is
> chosen as the monoclinic one.
>
> You can compare with the space group labels and positions in the lists
> offered by WYCKPOS in the Bilbao server. You will see that for the
> standard  " (C2/m): unique axis c" , the centering translation is in fact
> of type "A", i.e.  (0 1/2 1/2). Therefore, if you inspect the transformed
> structure proposed by sgroup, I would expect that you will find that it is
> just proposing to interchange the axes a and b, so that your B2/m (unique
> axis c) symmetry becomes in fact A2/m(unique axis c), which is the second
> standard and it is denoted by "(C2/m) unique axis c" (surely a very
> misleading notation, but it is not the fault of sgroup!).
>
> Regards,
>
> J. Manuel Perez-Mato
> Fac. Ciencia y Tecnologia,
> Universidad del Pais Vasco, UPV
> 48080 BILBAO,
> Spain
>
> tel. +34 946012473
> fax. +34 946013500
> *************************************************
>
>
>
>
>
>
> On Wed, October 17, 2012 10:48 am, Peter Blaha wrote:
>> I'm not an expert in sgroup, but yes, I believe the printed "names" of
> all
>> monoclinic spacegroups which have
>> different names for the unique axis c (vs. b) are not correct and I'll
> change them to B or b (instead of C or c)
>>
>> As far as I know, it does not affect anything else then the "comment" in
> the struct-files generated by sgroup.
>>
>>
>>
>> Am 16.10.2012 14:04, schrieb Gavin Abo:
>>> Dear Prof. Blaha and developers,
>>> I believe the attached struct file has appropriate parameters for the
> "12_B2/m" spacegroup. After I run "x sgroup" in w2web in Wien2k 12.1, it
>>> says "sgroup found: 12 (C 2/m)
>>> [unique axis c] cell choice 2".  I suppose that its most likely
> correct,
>>> but was just curious if perhaps the "C 2/m" is a typo and should be "B
> 2/m" in the character array
>>> "comnt_B_C2h_sgrp" in SRC_sgroup/sgrp_mon.c.
>>> Kind Regards,
>>> Gavin
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>> --
>>
>>                                         P.Blaha
>> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna Phone:
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>> http://info.tuwien.ac.at/theochem/
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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