The refinement of unit cell parameters from two-circle diffractometer measurements

Measurements of the crystal rotation angle (ω) for centred reflections provide the most reliable data for the refinement of unit cell parameters in two-circle single-crystal diffractometry. Zero-layer reflections are least affected by crystal misalignment, and can be used in a least-squares refinement of the corresponding reciprocal-cell parameters. The introduction of equations for a general crystal orientation allows the precise refinement of all six cell parameters from measurements of reflections on a range of layers for a misaligned crystal; only one crystal mounting is required. The possibilities of applying the general orientation algebra to intensity data collection are discussed.