Example why Platon/Addsym should be mandatory for crystallographers?

Pedro M. Matias matias at itqb.unl.pt
Wed Aug 16 08:15:04 EST 2000


Lachlan Cranswick wrote:

> I hope this isn't considered too "hyped up" but there is
> a new Platon/Addsym tutorial on the CCP14 site titled:
>
> "An example of why Platon/Addsym should be considered a mandatory
> program for all crystallographers"
>
>   http://www.ccp14.ac.uk/tutorial/platon/addsymb.htm
>
> This is based on the structure and spacegroups involved with the
> recent Short Communication in Acta Cryst "P1 or P-1? Corrigendum",
> Acta Cryst B56  (2000) 744 from Richard E. Marsh
>
> ------
>

...

I just tried out the example and it's really awesome what the program can do. However,

I don't like loose ends so I tried the triclinic cell on the CAD-4 software and TRANS C
gives the following results:

CD7>trans
M, R or C? [C]

Nr      FOM          Lattice   Bra

44     .000000       TRICLINIC    P     OBTUSE   (  .000)

      Solutions rejected on FOM:
Nr      FOM          Lattice   Bravais  Type

26     .005315       ORTHORHOMBIC F     ACUTE    (  .305)
29     .003778       MONOCLINIC   C     ACUTE    (  .216)
27     .005315       MONOCLINIC   C     ACUTE    (  .305)
28     .005315       MONOCLINIC   C     ACUTE    (  .305)
Transformation-number?26
Orientation matrix:
R11=   .201961 R12=  -.024318 R13=  -.005776
R21=  -.036941 R22=   .004454 R23=  -.032756
R31=   .131892 R32=   .038298 R33=   .000000

S11=   16.7936 S22=  481.2467 S33=  903.9512
S32=    2.3606 S31=    -.6605 S21=     .1967

A =     4.0980 B =    21.9373 C =    30.0658
Alp =  89.7949 Bet =  90.3072 Gam =  89.8746 Vol=    2702.8269

Reciprocal axes:
A*=      .2440 B*=      .0456 C*=      .0333
Alp*=  90.2057 Bet*=  89.6924 Gam*=  90.1265

In my opinion, this may mean one of two things:

1. not enough reflections for getting a good initial orientation matrix (insufficient sampling
of reciprocal space);

2. poorly aligned diffractometer.

There are probably other possibilities but these are the two that come to my mind...

Cheers,

Pedro Matias








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