I think you can find this also from the tables directly. The origin statement says
Origin at 23 i.e. on *any* special position with PGS 23 there are 4 of them in F23: 4a, 4b, 4c, 4d. They are listed at the end of the position table and of course agree with what Ian derived. BR -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Ian Tickle Sent: Wednesday, August 06, 2008 6:53 AM To: [email protected] Subject: Re: [ccp4bb] translation of atom sites and maps Hi David No F23 has 4 alternate non-equivalent origins (i.e. invariant amplitudes, different phases): (0, 0, 0) (1/4, 1/4, 1/4) (1/2, 1/2, 1/2) (3/4, 3/4, 3/4) You can of course have other combinations of these by adding any of the 4 F-centring translations. You can work this out from this table: http://www.ccp4.ac.uk/html/cheshirecell.html For F23 (in the list on the right, 2 lines from the bottom) you see that the Cheshire space group is I-centred (Im3m in the 1st column) and the Cheshire cell is (a/2, b/2, c/2). The lattice translation gives the origin at (1/2, 1/2, 1/2) and the combination of this with the I centring of the Cheshire SG gives the origins at (1/4, 1/4, 1/4) & (3/4, 3/4, 3/4). HTH!
