Histidine protonation is fraught, but a new quantum-mechanical method can provide insight into choices.

A new interaction energy model for molecular dimers, CE-1p, accurately calculates intermolecular interactions in molecular crystals. Improved treatment of dispersion and polarization helps it outperform existing models with accuracy comparable to advanced DFT methods with only a single fitted parameter.

A new crystallographic quantum-mechanical/molecular-mechanical model for the prediction of molecular crystal structures is described. Applications include polymorphic systems and molecules from the CCDC blind tests of crystal structure prediction.

Ion radii are derived from observed mean bond lengths (characteristic bond lengths) for 135 ions bonded to oxygen, fluorine, hydroxyl, chlorine and nitro­gen. Radii derived from quantum-mechanical calculations do not agree with radii derived from experimentally determined bond lengths. However, this problem is removed by recognition that ion radii determined from characteristic bond lengths are not a measure of the sizes of ions but proxy variables for characteristic bond lengths.

Here, the n = 2 satellite present for manganese-containing materials and across materials science has been successfully observed by applying the new technique of extended-range high-energy-resolution fluorescence detection (XR-HERFD), developed from high-resolution resonant inelastic X-ray scattering and HERFD, and the spectra have been predicted with new advanced theory.

A personal view on crystal structures is offered: past and present, ordered and disordered, static and dynamic, and problems solved and open.

Dudek and coworkers [Acta Cryst. (2020), B76, 322–335] report an integrated X-ray powder diffraction, NMR crystallography and crystal structure prediction study to determine crystal structures that could not have been determined using a single method. This is an important example that nicely illustrates the process of combining techniques and demonstrates the importance of careful validation.

For the first time, the use of experimentally derived molecular electron densities as ρ_B(r) in calculations based on frozen-density embedding theory (FDET) of environment-induced shifts of electronic excitations for chromophores in clusters is demonstrated. ρ_B(r) was derived from X-ray restrained molecular wavefunctions of glycylglycine to obtain environment densities for simulating electronic excitations in clusters.

This article describes the joint refinement program MOLLYNX dedicated to spin-resolved electron density distribution. Multipole and atomic orbital models are described and applications for organic and inorganic magnetic materials are discussed.

A new computational tool, CADEE (Computer-Aided Directed Evolution of Enzymes), is presented.