The eleven measured bands end at 1.522 A because their source says so in its
own words - "pure hexagonal ice has 11 diffraction rings between 4 and 1.5 A
resolution" - and its subject was detecting ice in deposited data, not masking
it. On a detector that reaches further, the rings it does not list are the ones
left in the data: on the strong rotation set just added to the battery, 44% of
every image's spots sit in ice bands, and beyond 1.5 A the spot list is ice and
nothing else, which is why the resolution estimate read the ice rather than the
crystal.
There is nothing measured to copy below 1.522 A, so the eight added bands are
calculated. Enumerating hkl is not enough and the code already said so: ice Ih
is P6_3/mmc with O on 4f, and most of what enumeration emits is extinguished by
the OXYGEN SUBLATTICE rather than by the space group - which is why (004) at
1.830 A and (104) at 1.657 A are missing from the measured list although they
sit inside its range and its reflection conditions allow them (for (00l) the
structure factor goes as cos(2*pi*l*z), and z ~ 1/16 kills l = 4). So compute
structure factors - oxygen only, the hydrogens being half-occupancy disordered
and weak to X-rays - and keep the lines reaching 3% of the strongest. That rule
REPRODUCES THE MEASURED ELEVEN EXACTLY and every line it drops inside their
range computes to zero, which is what makes it trustworthy below 1.522 A. It
stops at 1.170 A: below that the real lines fall to 2-3% while the extinct ones
rise to about 1%, and an oxygen-only calculation cannot separate them honestly.
Every added band was independently confirmed in the data - the spot-count
histogram of the strong set peaks at each of them and is empty between - and
every line the rule calls extinct is absent there too.
Costs, measured. The bands are inert above 1.6 A: on 38 of 39 battery sets the
profile ice score does not move at all, and the one that appeared to (a jet set,
1.25 -> 2.60) does not on the peak-excluded profile the score actually uses -
that was Bragg peaks in the plain profile, which is what the peak exclusion is
for. Where a detector does reach past 1.5 A the bands cover more of reciprocal
space: unchanged at 1.6 A, +7.4 points at 1.4 A, +16.5 at 1.18 A. On the strong
set that is 17% -> 27% of reflections held out of the scale fit, and it shows:
the spot resolution estimate improves from 1.33 to 1.46 A against a truth near
1.42, while CC1/2 falls 98.5 -> 97.6% and ISa 3.58 -> 3.37. Ice handling only
runs at all on a run that trips the ice gate, so a clean crystal pays nothing.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FBumeJVx4oeXxiBRpkrE5H
leonarski_fandClaude Opus 5
6516bc96af