Non‐Bonded Radii of the Atoms Under Compression

Abstract

We present quantum mechanical estimates for non‐bonded, van der Waals‐like, radii of 93 atoms in a pressure range from 0 to 300 gigapascal. Trends in radii are largely maintained under pressure, but atoms also change place in their relative size ordering. Multiple 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 under high pressure and permit an extension of chemical thinking 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. All data has been made available in an interactive web application.

Relating atomic energy, radius and electronegativity through compression

“…(3). 4,49 Calculated non-bonded radii also correlate reasonably well with Wigner-Seitz radii of bonded metallic elements compiled from shock-wave experiments, 56 but are, as expected, larger than such bonded radii.…”

“…The challenge of non-bonded/vdW radii can be solved computationally by considering single atoms compressed by a homogeneous non-reacting environment. 4,49 The propertiesradii, electronegativity as well as ground state electron configurations -of such compressed atoms have been determined in the pressure range from 0 to 300 GPa through full potential relativistic density functional theory calculations combined with the eXtreme Pressure Polarizable Continuum Model (XP-PCM). 4,49,57,58 We stress that by using this method we purposfully exclude the effects of both crystal structure and chemical bonding.…”

“…48 In this work, we rely on two revised scales of atomic vdW radii 3 and electronegativity 29 which have been extended to high pressure conditions (0 -300 GPa). 4,49 The scale of electronegativity used here is inspired by the work of Allen 26 and is defined as the average electron binding energy as T→0 K. 29,50 This definition of electronegativity establishes a connection with the total energy of a system through an energy decomposition analysis: 51 , (…”

Modeling Molecules Under Pressure with Gaussian Potentials

“…70 By contrast, the atomic van der Waals radii were found to decrease under pressure in an atom-specific manner. 71 In GOSTSHYP, however, the results for the carboncarbon bond lengths in trans-1,3-butadiene hardly change when adjusting the tessellation sphere scaling factors to different values while fixing the number of tessellation points per atom to 302 (Figure 2b). Even at high pressures of over 20 GPa, the difference in these bond lengths is only approx.…”

“…70 In this procedure, atom-centered spheres with the scaled (pressure-free) atom-specific van der Waals radii are superimposed and the overlapping regions are omitted, leading to a physically sound tessellation field. Since atomic van der Waals radii are in fact pressure-dependent, 71 in the following we refer to the scaling factors of the atomcentered spheres as the "tessellation sphere scaling factors". The dependence of the results calculated with GOSTSHYP on the technical parameters of the tessellation routine, i.e.…”