Re: [ccp4bb]: ab initio

[Ethan Merritt <merritt@u.washington.edu>]

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On Tuesday 11 February 2003 08:34, Bernhard Rupp wrote:
> Is there a consensus or preference what 'ab inito phasing'
> exactly means?

Interesting question.  I am not aware of a consensus definition,
so I'll take a stab at one.

1) It should mean "starting only from unit cell information and 
    Bragg intensities".  That rules out MR, but unfortunately not
    yet MIR.

2) So we add "measured from a single crystal", which rules out
    MIR but leaves MAD.  

3) To rule out MAD we could add "at a single wavelength".
    This still leaves SAS in addition to direct methods, but maybe 
    that is OK.

The extreme case, of course, is simply to say 
4) "ab initio" = "direct methods".

I'd accept either 3 or 4. What do other people think?

-- 
Ethan A Merritt       merritt@u.washington.edu
Biomolecular Structure Center Box 357742
University of Washington, Seattle, WA 98195