Crystal Unit Cell Question

Uncle Al UncleAl0 at hate.spam.net
Thu Nov 15 17:38:51 EST 2001


Bev Vincent wrote:
> 
> "Uncle Al" <UncleAl0 at hate.spam.net> wrote in message
> news:3BF42339.6F5822E at hate.spam.net...
> > Uncle Al asks a probably silly and very obvious question about some
> > crystal data...
> >
> > REFERENCE STRUCTURE = 20626   A,B,C =   5.482   5.482   5.173
> >    ALPHA,BETA,GAMMA =  90.000  90.000 120.000    SPGR =173 P63
> >    3   0 CODEN=   46025 SYMOPS=  389
> >   40     RFAC= 2.1 ERRFLAG=0 (C-C)ESD=0
> >    1 Li1    0.00000   0.00000   0.07830
> >    2 O1     0.24750   0.34220  -0.16200
> >    3 I1     0.33333   0.66667   0.00000
> >
> > Lithium iodate, LiIO(3), has two formula units in its unit cell:
> >
> > 2 lithiums
> > 2 iodines
> > 6 oxygens
> >
> >   ----- Where are the rest of the atoms? -----
> 
> Space Group P63 (#173) has the following symmetry operators:
> 
> 1)    +X,    +Y,    +Z           2)    -Y,    +X-Y,    +Z
>  3)    -X+Y,    -X,    +Z       4)    -X,    -Y, 1/2+Z
>  5)    +Y,    -X+Y, 1/2+Z    6)    +X-Y,    +X, 1/2+Z
> 
> Take the above coordinates for Li1, I1 and O1 and apply these operations. If
> an atom is on a special position, some of these operations will return the
> same coordinates (e.g. 0, 0, .0783 produces the same coordinates for
> operators 1-3 and the second position -- 0, 0, 0.5783 -- for operators 4-6).
> 
> >  REFERENCE STRUCTURE = 47670   A,B,C =   4.913   4.913   5.405
> >    ALPHA,BETA,GAMMA =  90.000  90.000 120.000    SPGR =154 P3221
> >    2   0 CODEN=   83849 SYMOPS=  398
> >   40     RFAC= 2.4 ERRFLAG=0 (C-C)ESD=0
> >    1 Si1     0.46980   0.00000   0.16667
> >    2 O1      0.41380   0.26510   0.28710
> >
> > Alpha-quartz, SiO(2), has three formula units in its unit cell,
> >
> > 3 silicons
> > 6 oxygens
> >
> >    ----- Where are the rest of the atoms? -----
> 
> P3221 (#154) has these operators:
> 
> 1)    +X,    +Y,    +Z           2)    -Y,    +X-Y, 2/3+Z
>  3)    -X+Y,    -X, 1/3+Z     4)    +Y,    +X,    -Z
>  5)    -X,    -X+Y, 2/3-Z      6)    +X-Y,    -Y, 1/3-Z
> 
> Same game as before.
> 
> Bev Vincent
> Rigaku/MSC
> http://www.RigakuMSC.com

I should have been a social activist.  Exercise of objective
competence is such a nuisance...  I limbered up my HP-15C and visited

http://sbl.salk.edu/~jason/Public/spacegroup.html#173

Clever folks those x-ray crystallographers.

Thanx guyss!  I'll withdraw my post now.

-- 
Uncle Al
http://www.mazepath.com/uncleal/
 (Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?"  The Net!





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