Hi Careina

The obvious answer is to look it up in International Tables vol. A.
If you don't have access to that you can look up the text file
$CLIBD/syminfo.lib in the CCP4 distribution and work it out from
there.  Fpr a given space group you need to count the number of
'symop' lines.  That's the number of asymmetric units in the primitive
cell.  If you want the number in a centred cell, also count the number
of 'cenop' lines: that's the number of centring translations, so to
get the total no of a.u.'s in the centred cell you would multiply
these two numbers.

I'm afraid there isn't an easier way, for example you can't get it
straightforwardly from the space group symbol.

HTH

-- Ian

On 2 August 2012 09:37, Careina Edgooms <[log in to unmask]> wrote:
> Dear ccp4
>
> I ask a very fundamental question because I have not had formal training in
> this and I would like to understand.
> How can I obtain the multiplicity (z) from the space group? So for example
> if the space group is P222 how do I know that there are 4 monomers in the
> unit cell? Or if it is P422 then there is 8? I am only concerning myself
> with a primitive lattice for now because I am sure the others are more
> complicated.
> thanks
> Careina