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> Now, it is not at all prohibitive to calculate multiple 
> structures, even at low resolution. Provided the number of 
> fitted parameters was chosen appropriately, we could simply 
> ask, "What are ALL the structures that are ideal in terms of 
> geometry and that also best fit to the determined atomic 
> positions?" Just like NMR people do it. We can simply run 
> many independent refinements using simulated annealing, or 
> some other randomizer, and calculate all structures that are 
> within kT or some other criterion. We would not violate any 
> data/parameter ratio rules, because we are not refining the 
> structures simultaneously. Every single structure would still 
> be ideal in terms of geometry, and all structures taken 
> together as an ensemble would well describe the (averaged) 
> crystal structure. We would then use rmsd's to describe 
> deviations between all ideal structures that fit the data, 
> just like in NMR, and get rid of the confusing rmsd's for 
> bond lengths and angles.

That's been done, of course: 

Furnham N, Blundell TL, DePristo MA, Terwilliger TC, "Is one solution good
enough?".  Nature Structural & Molecular Biology 13, pp184-5 (2006). 

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