The influence of refinement strategies on the wavefunctions derived from an experiment

The synergy between theory and experiment found in the X-ray wave function refinement, XWR, makes it one of the most compelling techniques available for chemical physics. The foremost benefit of XWR-obtaining wave functions constrained to experimental data-is at the same time its Achilles heel, because of the dependency of the results on the quality of both empirical and theoretical data. The purpose of this work is to answer the following; What is the effect of the refinement strategy and manipulation of input data in the physical properties obtained from XWR? With that in mind, cutoffs based in data resolution and F/σ(F) ratios were applied for both steps of XWR, the Hirshfeld atom refinement (HAR) and the X-ray constrained wavefunction fitting (XCW), for four selected systems: sulphur dioxide, urea, carbamazepine and oxalic acid. Also, the effects of changing the weighting scheme or the method to transform σ(F 2) to σ(F) were analysed. The results show that while HAR always reaches the same result, XCW is extremely sensitive to the crystallographic PREPRINT: Acta Crystallographica Section B A Journal of the International Union of Crystallography 2 data manipulation. This is a result of the variability of the experimental uncertainties for different resolution shells, and of not having proper standard uncertainties. Therefore, the use of distinct constraints for each resolution interval in XCW is proposed to fix this instability.