We apply for the first time the transferable aspherical atom model (TAAM) for the refinement of a metal complex structure against 3D ED data. Our results show that TAAM significantly outperforms the independent atom model (IAM) by more accurately depicting the electrostatic potential, particularly in low-resolution ranges. We found that using TAAM for organic ligands is more important than an accurate description of the metal centre in the refinement against 3D ED data.

Refinement of a small-molecule crystal structure against electron diffraction data is now available in the MoPro software with the implementation of electron scattering factors, using a spherical or multipolar atom model.

It is now possible to integrate the transferable aspherical atom model (TAAM) with NoSpherA2 and refine X-ray diffraction data of disordered, twinned, co-crystal, covalent organic framework and metal–salt structures in a short period of time. A new hybrid approach, allowing a combination of the independent atom model, Hirshfeld atom refinement and TAAM in one structure refinement, is introduced which benefits from the advantages of each method.

This paper presents the advantages of using the transferable aspherical atom model of macromolecular structure refinement against ultrahigh-resolution X-ray data over the classic independent-atom model approach in terms of final crystallographic statistics, the description of atomic displacement parameters and the quality of electron-density maps.

Hirshfeld atom refinement (HAR) combined with fragmentation and atomic density transferability was tested on various systems, both polymeric and disordered. HAR was significantly faster with these adjustments, reducing computational time for larger systems with only a modest drop in accuracy.

PeakProbe facilitates the automated modelling of ordered solvent in macromolecular crystal structures by analysing features of the electron density and chemical environment surrounding a given coordinate. The extracted data are transformed to a resolution-independent score space and likely solvent models are predicted based on the frequency distributions observed in a large-scale sample of the PDB.

Contributions of different physical effects (thermal smearing, relativity, electron correlation, basis set, environment and/or atomic contributions) to the structure factors of heavy-element compounds are inspected. Relativistic Hirshfeld atom refinement yields an almost perfect agreement with reference geometries in this theoretical pilot study, showing the usefulness of the employed methodology.

Anisotropic atomic displacement parameters obtained separately from highly accurate X-ray and neutron diffraction data are compared, and it is established that Hirshfeld atom refinement of X-ray data can provide structural parameters that are as accurate as those from neutron data.

A new aspherical scattering factor formalism was implemented in SHELXL. It relies on Gaussian functions and can optionally complement the independent atom model to take into account the deformation of electron-density distribution due to chemical bonding and lone pairs. The automated atom-type assignment was derived from the invariom formalism.

Precomputed multipolar electron scattering factors are employed for electron crystallography. Because this takes into account the fact that atoms are partially charged and aspherical, model fitting statistics and atomic thermal parameters are visibly improved.