The Van Der Waals Radii at High Pressure and the Atoms-Under-Pressure Database

We describe a quantum mechanical model for calculating van der Waals radii of non-reactively compressed atoms. Radii are presented for 93 atoms in a pressure range from 0 to 300 gigapascal. Trends in radii are shown to be largely maintained under pressure compared to ambient conditions, but atoms also change place in their relative size ordering. Isobaric contractions of radii are predicted and are explained by pressure-induced changes to the electronic ground state configurations of the atoms. The presented radii are predictive of drastically different chemistry and physics under high pressure and permit an extension of atom-based rationales to different thermodynamic regimes. For example, they can aid in assignment of bonded and non-bonded contacts, for distinguishing molecular entities, and for estimating available space inside compressed materials. An open interactive web application, the Atoms-Under-Pressure Database, containing radii, electronegativities and atomic ground state electron configurations for compressed atoms is also demonstrated.