Relativistic effects on electronic pair densities: a perspective from the radial intracule and extracule probability densities

TL;DR

This paper investigates how relativistic effects influence electronic pair densities, revealing that scalar-relativistic effects reduce mean inter-electronic distances and increase electron-electron repulsion, with implications for electronic structure calculations.

Contribution

It provides the first detailed analysis of relativistic impacts on intracule and extracule pair densities, highlighting changes in inter-electronic distances and repulsion energies.

Findings

Relativistic effects decrease mean inter-electronic distances.

Scalar-relativistic effects increase electron-electron repulsion.

Preliminary results indicate correlation effects do not negate these trends.

Abstract

While the effect of relativity in the electronic density has been widely studied, the effect on the pair probability, intracule, and extracule densities has not been studied before. Thus, in this work, we unveil new insights related to changes on the electronic structure caused by relativistic effects. Our numerical results suggest that the mean inter-electronic distance is reduced (mostly) due to scalar-relativistic effects. As a consequence, an increase of the electron-electron repulsion energy is observed. Preliminary results suggest that this observation is also valid when electronic correlation effects are considered.