midas-hkls 0.1.0

Pure-Python crystallography & HKL list generator. sginfo-equivalent: 230 space groups via Hall-symbol parser.

midas-hkls

Pure-Python crystallography & HKL list generator. sginfo-equivalent: all 230 space groups via Hall-symbol parsing, no C dependencies at runtime.

What it provides

• SpaceGroup — load by number, Hermann-Mauguin symbol, or Hall symbol; expose symmetry operations, systematic absences, equivalent reflections, multiplicities, Laue class, centering.
• Lattice — direct/reciprocal metric tensors, d-spacings, Bragg 2θ, with per-crystal-system convenience constructors.
• generate_hkls() — enumerate Laue-unique allowed reflections within a d-spacing or 2θ cutoff, sorted by d-descending, with multiplicities.
• CLI: midas-hkls gen|info|list (drop-in for GetHKLList).

Quick start

from midas_hkls import SpaceGroup, Lattice, generate_hkls

sg  = SpaceGroup.from_number(225)              # CeO₂ / Cu / Au / NaCl  (Fm-3m)
lat = Lattice.for_system("cubic", a=5.411)     # Å
refs = generate_hkls(sg, lat, wavelength_A=0.173, two_theta_max_deg=15.0)

for r in refs:
    print(r.ring_nr, (r.h, r.k, r.l), r.d_spacing, r.two_theta_deg, r.multiplicity)

CLI

midas-hkls gen --sg 225 --lat 5.411 5.411 5.411 90 90 90 --wavelength 0.173 \
               --two-theta-max 15.0 -o ceo2.csv
midas-hkls info --sg "Fm-3m" --ops
midas-hkls list

Parity with sginfo C library

midas-hkls is parity-tested byte-for-byte against MIDAS's GetHKLList (sginfo):

• Ring count, ring d-spacing, ring 2θ, ring multiplicity match exactly across CeO₂, LaB₆, Si, α-Fe, α-Ti, calcite, Pnma, P21/c.
• All 230 space groups parse without error and have correct Friedel-corrected Laue-class group orders.

Run pytest to exercise the parity matrix.

Conventions

• Lattice constants in Å; angles in degrees.
• Wavelengths in Å.
• Symmetry operations stored as integer Seitz matrices over translation base STBF=12 (so 1/2 → 6, 1/3 → 4, 1/4 → 3, etc.) — exact-arithmetic absence detection, no float fuzz.
• Equivalent HKLs include Friedel pairs (centric structure factor under X-ray Laue symmetry).

Roadmap (post v0.1.0)

• CIF reader (io/cif.py).
• Atomic form factors (Cromer-Mann) and structure factors.
• Anomalous scattering (Henke / Cromer tables).
• Wyckoff positions tables (currently only general position is exposed).
• Origin-choice and alternate-setting transformations beyond what sginfo's extension field provides.

Origin

The 530-entry Hall-symbol table is extracted verbatim from sginfo (© 1994-96 Ralf W. Grosse-Kunstleve, public domain) so that midas-hkls and MIDAS's existing C tools resolve the same standard setting for every space group.