The free-set hash was keyed on the Laue ASU of the merging group, so a twin
law - a lattice symmetry the crystal lacks - put nearly every free
reflection's twin mate in the working set (measured: 97-98% of the
free-touching twin pairs mixed, on the main P3121 output of 6iu9 and on
every law of the 6toc P1 cross-check), and each file of one crystal carried
a different free set (P1 vs merged agreed on 88-92% of reflections).
With the cell given, the key is now the reflection's orbit, Friedel mate
included, under the lattice holohedry: the metric point group of the cell
(gemmi Le Page two-folds, 3 deg obliquity, lattice of the cell's own basis
vectors so every file gets the same group; this contains the merging
group). Twin mates share a flag, and the merged MTZ/mmCIF, the P1
cross-check and any subgroup re-merge carry one free set (nested where the
small-data floor lifts the fraction of one file more than another). This is
phenix.refine's default (use_lattice_symmetry). Where the cell does not
carry the merging group, the merging group's key is used as before. The
small-data floor still counts reflections of the merging group, so the free
fraction is unchanged. Reference free sets are untouched.
On 6toc, 6iu9, 5j23: mixed twin pairs 0 for every law; P1 and merged flags
agree on 100% (6iu9, 5j23) and nested on 6toc; free fraction 0.050-0.051 as
before (6toc merged 0.086, floor unchanged). Intensities and space groups
identical to rc171.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
54fcb3cbcb
