RSCU-SOS – a rapid searching and centering utility routine for single-crystal X-ray diffraction studies at simultaneous high pressures and temperatures

Single-crystal diffraction studies conducted in a diamond-anvil cell (DAC) under high pressure (P) and temperature (T) conditions often have the annoying problem that the sample orientation changes when P and/or T is changed. It is essential to quickly find and recenter the diffraction peaks in order to refine a new orientation matrix and further collect diffraction data from the single-crystal at the changed P–T conditions. This paper presents a rapid searching and centering utility (RSCU) routine to deal with the orientation-shifting problem in high P–T DAC single-crystal diffraction studies. The RSCU routine starts with a refined reflection list from previous P–T conditions and conducts a search in the pattern of a spiral of open square (SOS) for diffraction peaks in the χ−φ plane. Following the peak search, it conducts 2θ, ω and χ scans to center the diffraction peaks and then performs a least-squares curve fit to refine the true diffraction positions in 2θ, ω, χ and φ space. The RSCU routine incorporates the Hamilton method to eliminate errors due to sample misalignment. Reflections are sorted to minimize the driving time between successive peaks. The algorithm of the routine is given in symbolic logic so that it can be translated and inserted into other crystallographic software packages.