Structure-specific restraints for least-squares refinement from tight binding quantum chemistry

Disordered crystal structures Underlying challenges posed by disorder are inaccurate atomic positions in a crystal structure. Their determination is especially difficult when atoms with disordered split sites are closer to each other than the resolution of a single-crystal diffraction experiment. While non-hydrogen atom positions can usually be resolved, the situation is even more difficult for hydrogen-atom positions due to their scattering power [3], especially when these are rotationally disordered. This asks for a "quantum-chemical aide" We have therefore extended the functionality of the program Baerlauch The output of Baerlauch cluster computations then (among other results) provides bond distance and bond angle restraints for use in classical independent-atom model refinements e.g. with SHELXL. Results of this generally applicable workflow to optimize crystal structures (or only their hydrogen atoms) are presented.