Note : By default up to 20 % of the atoms are allowed as mis-fits (i.e. atoms falling out of
the default criteria or with missing symmetry related counterparts). The EXACT sub-
keyword will put this value to zero.
Standard, Alternate and Non-standard Settings
ADDSYM will by default transform all unit cells to a standard setting. For triclinic
structures this implies a reduced cell with a
degrees or all angles less than 90 degrees. For monoclinic structures this implies the
b-axis
unique, C centered where I centered might give a closer to 90 degrees beta angle and
c glide
preferred to
n glide.
Missed Symmetry Example #1
In the order of 10 % of the structures published in Space group Cc can be shown to be better
described with higher symmetry. A common case is the omission of an inversion centre.
This example shows how to detect and correct automatically for that problem.
TITL AACRUB Cc R=0.0380
CELL 14.2460 6.9040 17.6870 90.000 97.190 90.000
CESD 0.0020 0.0010 0.0020 0.000 0.010 0.000
SPGR Cc
Ru(1) 0.22852 0.15210 0.36523
Ru(2) 0.12035 0.34630 0.40847
O(1) 0.22860 0.32200 0.27210
O(2) 0.33730 0.30800 0.42380
O(3) 0.22800 -0.00410 0.45390
O(4) 0.12660 -0.00400 0.30750
O(5) 0.12440 0.52300 0.31530
O(6) 0.22860 0.49900 0.46410
O(7) 0.11900 0.17000 0.49890
O(8) 0.02400 0.17600 0.35380
O(9) 0.33580 -0.06800 0.32270
O(10) 0.00210 0.52300 0.44990
C(1) 0.18130 0.46000 0.26420
C(2) 0.17370 0.61600 0.20200
C(3) 0.31360 0.45900 0.46460
C(4) 0.39210 0.55600 0.50520
C(5) 0.17690 0.01400 0.50280
C(6) 0.16480 -0.08500 0.57740
C(7) 0.04180 0.04600 0.31500
ADDSYM OUTPUT FOR EXAMPLE 1
ADDSYM - CHECK (cf. MISSYM (C): Le Page, Y., J. Appl. Cryst. (1987), 20,
264-269; J. Appl. Cryst. (1988), 21, 983-984)
------------------------------------------------------------------------------
- This ADDSYM Search is run on ALL NON-H Chemical Types
- Number of Input Atoms Included in Search = 25
- The Structure implies the following Symmetry Elements subject to the Criteria:
1.00 Deg., (metric) 0.25 Ang. (distances) and 0.45 Ang. (inv. and transl.)
Symm. Input Reduced (Ang) (Deg) (Ang) Input Cell
Elem Cell Row Cell Row d Type Dot Angle Max. dev. x y z
--------------------------------------------------------------------------------
c [ 0 1 0] [-1 0 0] 6.903 2 2 0.00 0 through 0 0 0