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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dear Jacob, you don't necessarily want to find the global minimum - the global minimum of the target function might be an overfitted set of parameters. At low resolution the (local) minimum you do want to reach may not be very sharp. This is best illustrated by shelxl that prints the maximum shift each cycle, and with poor data to parameter ratios and poor data quality you often find individual atoms moving randomly around (by e.g. 0.02A). Cheers, Tim On 11/27/2014 11:14 PM, Keller, Jacob wrote: >> We just had a chance to read this most interesting discussion. We >> would agree > with Ian that jiggling or SA refinement may not be needed if > refinement can in fact be run to convergence. However, this will be > difficult to achieve for large structures, especially when only > moderate to low resolution data are available. > > I find this interesting—is refinement convergence related to > resolution? Is this because the structure-landscape is not > sufficiently defined to find the real global minimum? I wonder what > would happen if Ian Tickle’s test were done on many structures, and > results examined as a function of resolution? Predictions? I guess > generally there are more ways to fit fewer data points than many, > but then perhaps refinement convergence would be more dependent on > parameter:observation ratios than resolution per se, although > quantities are closely related all things being equal. > > JPK > - -- - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iD8DBQFUeDE1UxlJ7aRr7hoRAoqXAJ9ycLFovlr15oj447XceDmtrCkXlQCgqHC/ ytJnZ1lv4GdBIwuDzqniLxU= =sxDL -----END PGP SIGNATURE-----