Ad hoc diffractometer

ad_hoc_diffractometer is a pure-Python package for calculating multi-circle diffractometer operations in reciprocal space for X-ray and neutron crystallography. It is built around a key design principle: any multi-circle diffractometer geometry can be fully described by the caller — no geometry is hard-coded, and new geometries require no changes to the package itself.

Its only runtime dependency beyond the Python Standard Library is NumPy — no scipy, sympy, or other scientific libraries are required.

Note: The package assumes monochromatic radiation throughout. All diffraction calculations are performed at a fixed wavelength.

Features

• A class-based description of diffractometer stages (rotary axes) and their stacking order
• Predefined factory functions for standard synchrotron and laboratory diffractometer geometries (psic, fourcv, fourch, sixc, kappa families, zaxis, s2d2, fivec)
• Crystallographic lattice calculations (B matrix, reciprocal lattice)
• U and UB matrix computation from orienting reflections
• Forward diffraction calculations (hkl → motor angles), with diffraction modes controlling which stages are free, fixed, or coupled
• Reciprocal-space trajectory planning

Quick start

import ad_hoc_diffractometer as ahd

# Four-circle geometry (Busing & Levy 1967, vertical scattering plane)
g = ahd.fourcv()
g.wavelength = 1.5406          # Å (Cu Kα)
g.sample.lattice = ahd.Lattice(a=5.431)  # cubic silicon

print(g.summary())

See the Quick Start guide for a step-by-step walkthrough that builds the same geometry without the factory function — choosing a coordinate basis, stacking stages, defining diffraction modes, and running a forward calculation.

Install

pip install ad_hoc_diffractometer

For development:

git clone https://github.com/prjemian/ad_hoc_diffractometer
cd ad_hoc_diffractometer
pip install -e .[dev]

See the documentation for full installation options (conda, uv, hatch) and usage guides.

References

Papers describing the diffractometer geometries provided:

• Busing & Levy (1967) — fourc. Acta Cryst. 22, 457–464.
• Bloch (1985) — zaxis. J. Appl. Cryst. 18, 33–36.
• Vlieg et al. (1987) — fivec. J. Appl. Cryst. 20, 330–337.
• Lohmeier & Vlieg (1993) — sixc. J. Appl. Cryst. 26, 706–716.
• Evans-Lutterodt & Tang (1995) — s2d2. J. Appl. Cryst. 28, 318–326.
• You (1999) — psic. J. Appl. Cryst. 32, 614–623. DOI: 10.1107/S0021889899001223
• ITC Vol. C §2.2.6 (2006) — kappa. DOI: 10.1107/97809553602060000577
• Walko (2016) — geometry survey. Reference Module in Materials Science and Materials Engineering, Elsevier.