The de-novo space-group search runs its point-group correlation only on reflections
with I/sigma >= 3, but the Diederichs error model floors merged I/sigma at the
asymptotic ISa = 1/b. On a weakly-diffracting crystal a few edge-of-sweep truncated
fulls (rocking curve captured far below 1) inflate the error-model b term, dropping
ISa below 3 so no reflection clears the gate: every operator gets zero pairs and the
point group collapses to P1 (or a low subgroup). The chi^2 self-consistency guard is
likewise corrupted by those zingers.
Raising the rotation default of --min-captured-fraction from 0.5 to 0.7 drops those
partiality-extrapolated fulls, lifting ISa back above the gate and cleaning the
intensity statistics, so the search recovers the true symmetry. On the F-cubic Benas
crystals: Benas_3 P4 -> F432 (CC1/2 78% -> 98%) and Benas_7 P1 -> P6122 (CC1/2 40% ->
99%). Benas_7's data supports hexagonal P6122, not cubic F432 - the cubic 3-fold/4-folds
fail the merge self-consistency test - matching XDS.
Full /data/rotation_test battery: every other crystal keeps its exact space group; the
only cost is a little multiplicity from the extra dropped edge-fulls on a few weak/
narrow-sweep crystals (worst completeness -7% on EP_cs_01-24, whose CC1/2 nonetheless
rises), while several crystals' CC1/2 improve.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
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