Recent methodological developments and their applications in quantum crystallography are reviewed, with an eye towards near-future advancements in this research field.

Kinematical Hirshfeld atom refinement has been applied to electron diffraction data for the first time, but the effect of using an aspherical atom model is overshadowed by dynamical scattering effects. Dynamical independent atom model refinement leads to significantly improved structures, suggesting that dynamical refinement is also necessary to obtain the full advantage of using aspherical atom models.

By implementing the aspherical atom model to normal mode refinement, we obtained accurate structures [including H-atom positions and anisotropic displacement parameters (ADPs)] and heat capacity from single-crystal X-ray diffraction data.

Understanding dynamic processes in molecular crystals is becoming crucial for the development of next-generation smart crystalline materials. In this context, Zwolenik & Makal [(2025). IUCrJ, 12, 23–35] shed light on the complex dynamics–structure–properties relation of a pyrene derivative by correlating molecular and lattice anharmonic vibrations with the unusual thermal expansion of the compound.

A recently discovered β polymorph of 1,3-diacetylpyrene has turned out to be a prominent negative thermal expansion material. Its unique properties can be linked to anharmonic oscillations in the crystal structure. The onset and development of anharmonic behavior have been successfully tracked over a wide temperature range by single-crystal X-ray diffraction experiments. Sufficient diffraction data quality combined with modern quantum crystallography tools allowed a thorough analysis of the elusive anharmonic effects for a moderate-scattering purely organic compound.

We demonstrate that applying the alternative electron density partition in a Hirshfeld atom refinement may significantly improve the accuracy of hydrogen atom parameters. The new partition leads to less overlapping atomic densities. As a result, hydrogen atom parameters are less dependent on the structural parameters of their neighbours and their inaccuracies.

The next-generation machine-learning force field FFLUX is applied to ice polymorphs Ih, II and XV. Under the quasi-harmonic approximation, Gibbs free energies are calculated using FFLUX at a significantly reduced computational cost compared with the commonly used density functional theory methods. However, the parametrized non-bonded potentials negatively affect the accuracy of the model, leading to large errors in the free energies calculated.

The methodology proposed combines the DFT calculations and photoelasticity caused by uniaxial compression of the crystal lattice, with particular emphasis on its anisotropy. It can be considered as part of optical engineering aimed at preliminary assessment of the photoelastic properties of crystal materials, thus assisting in their selection for synthesis and relevant applications.

Interacting quantum atoms and source function studies on a series of halogen-bonded complexes between substituted pyridines and X₂ or XCN molecules (X = I, Br) focus on the combined role played by the X and N interacting pairs and their local environment.

This study employs quantum crystallography to elucidate the selectivity of nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen, flurbiprofen, meloxicam and celecoxib, for cyclooxygenase-1 and cyclooxygenase-2 enzymes by analyzing binding energy and electrostatic interactions. The findings reveal key structural determinants of NSAID selectivity, providing valuable insights for the rational design of safer and more effective anti-inflammatory drugs.

We analyse both charge and spin degrees of freedom in the electron density of NiX₂(3,5-lutidine)₄ (X = Cl, Br and I) to understand the nature of magnetic exchange via through-space Ni²⁺–halide⋯halide–Ni²⁺ interactions. We propose that remarkably strong interactions can occur in coordination polymers when the exchange pathway is `switched-on' by just very weak covalency and enhanced by a charge density that is naturally localized on the ligand's atoms that bond to the magnetic metal ions.