Alan
I'm afraid that the cif files weren't overly good
ones - I don't normally use them. For the R-3m the Li 1/2 fractional
coordinate is for the z, not y. The structures are related by a �3a x �3a relationship with Z = 3
for the R-3m and Z = 9 for the P3112.
Here are the STR files. You can
refine the 3a and 3b positions for the P3112, but there is a strict relationship
that has to be maintained between the x and y coordinates - I have to do it in
launch mode to make it work. It's a very picky space group to work
with.
Pam
Dr Pamela Whitfield CChem MRSC
Energy
Materials Group
Institute for Chemical Process and Environmental
Technology
Building M12
National Research Council Canada
1200 Montreal
Road
Ottawa ON K1A 0R6
CANADA
Tel: (613) 998
8462 Fax: (613) 991
2384
Email: <mailto:[EMAIL PROTECTED]>
ICPET
WWW: http://icpet-itpce.nrc-cnrc.gc.ca
-----Original
Message-----
From: alan coelho [mailto:[EMAIL PROTECTED]]
Sent:
October 18, 2004 4:16 PM
To: [EMAIL PROTECTED]
Subject: RE: troublesome
unit cell
Pam,
As a developer and someone who uses other
software to test against, I
have been following the discussion with interest.
This is a complex area
and it goes to show the importance of having a few
programs if only for
testing purposes.
I am puzzled by your cif data
however as I cant get past verifying the
equivalence of the number of
equivalent positions for the Li site.
In R-3m you have as fractional
atomic coordinates for Li1:
x = 0 y = 0.5
and z = 0
For P3112 you have three Li sites with x, y, z's
as
0.77780 0.22220 0.83330
0.11110 0.88890 0.83330
0.44440 0.55560
0.83330
which translates to:
0.77780 0.22220 5/6
0.11110
0.88890 5/6
0.44440 0.55560 5/6
Listed below are equivalent positions
for a general site.
What I dont understand is that for R-3m I get 9
non-overlapping fully
occupied equivalent positions within the unit cell with
a volume of
101.2975.
For P3112 I get 18 non-overlapping equivalent
positions with a volume
three times as large of 303.8968. I was expecting to
get 27 if the two
structure were to be equivalent.
Thus, from your cif
data I am left to conclude that I am generating the
wrong number of
equivalent positions, or, if I am generating the correct
number of equivalent
positions then the two cif data sets should indeed
give different powder
patterns.
Have you checked what the number of non-overlapping fully
occupied
equivalent positions for Li should be for the two
structures.
alan
P3112
xyzs
{
-x+y, -x, z-1/3
-x+y, y,
-z+1/3
-y, -x,
-z-1/3
-y, x-y,
z+1/3
x, y,
z
x, x-y, -z
}
6
R-3m
xyzs
{
-x,
-x+y, -z
-x, -y,
-z
-x+y, -x,
z
-x+y, y,
z
-y, -x,
z
-y, x-y,
z
y, -x+y,
-z
y, x,
-z
x-y, -y,
-z
x-y, x,
-z
x, y,
z
x, x-y,
z
' +(-1/3, 1/3, 1/3)
-------------------------
-x-1/3,
-x+y+1/3, -z+1/3
-x-1/3, -y+1/3,
-z+1/3
-x+y-1/3, -x+1/3,
z+1/3
-x+y-1/3, y+1/3,
z+1/3
-y-1/3, -x+1/3,
z+1/3
-y-1/3, x-y+1/3,
z+1/3
y-1/3, -x+y+1/3,
-z+1/3
y-1/3, x+1/3,
-z+1/3
x-y-1/3, -y+1/3,
-z+1/3
x-y-1/3, x+1/3,
-z+1/3
x-1/3, y+1/3,
z+1/3
x-1/3, x-y+1/3,
z+1/3
' +(1/3, -1/3, -1/3)
-------------------------
-x+1/3,
-x+y-1/3, -z-1/3
-x+1/3, -y-1/3,
-z-1/3
-x+y+1/3, -x-1/3,
z-1/3
-x+y+1/3, y-1/3,
z-1/3
-y+1/3, -x-1/3,
z-1/3
-y+1/3, x-y-1/3,
z-1/3
y+1/3, -x+y-1/3,
-z-1/3
y+1/3, x-1/3,
-z-1/3
x-y+1/3, -y-1/3,
-z-1/3
x-y+1/3, x-1/3,
-z-1/3
x+1/3, y-1/3,
z-1/3
x+1/3, x-y-1/3, z-1/3
}
36
/* Fractional atomic coordinates for for
R-3m
Li1
0.00000
0.50000 0.00000
0.50000 0.00000
0.00000
0.50000
0.50000 0.00000
0.66667 0.83333
0.33333
0.16667
0.33333 0.33333
0.16667 0.83333
0.33333
0.33333
0.16667 0.66667
0.83333 0.66667
0.66667
0.83333
0.16667 0.66667
*/
/* Fractional atomic coordinates for
P3112
Li
0.44440
0.22220 0.50000
0.77780 0.22220
0.83333
0.77780
0.55560 0.16667
Li
0.77780 0.88890
0.50000
0.11110
0.88890 0.83333
0.11110 0.22220
0.16667
Li
0.11120
0.55560 0.50000
0.44440 0.55560
0.83333
0.44440
0.88880 0.16667
*/
LiMnNiCoO2 R-3m.str
Description: Binary data
Li3MnCoNiO6.str
Description: Binary data
