[phenixbb] XN-refinement

Pavel Afonine pafonine at lbl.gov
Fri Oct 14 18:23:25 PDT 2016

Hi Tim,

> in 1978, there was a version of shelxl for joint refinement of X-ray and
> neutron data (Orpen, Pippard, Sheldrick, Acta Cryst (1978) B34 2466-2472)
> The paper now cited for the Hirshfeld test (Acta Cryst A32 (1976) pp239)
> discusses the combination of refinement against neutron and X-ray data,
> including many references to Phil Coppens, although I cannot tell if this
> refers to joint refinement.

thanks a lot, this is certainly good to know! I will have a look at 
these papers.

> For macromolecular data, the restraints often contribute greatly to the data
> to parameter ratio, e.g. for a shelxl refinement of 1L2K, there are about 1300
> reflections, 40,000 restraints and 9,000 parameters. And since the starting
> structure has often already been refined against the X-ray data anyhow, why do
> it again and risk a mix-up with your points of interest?

This is just to use more information in refinement, and you are correct 
about the risks. So our future developments focus on eliminating these 
risks while still using more information.

All the best,

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