  Short-range repulsion within inter-molecular force fields is conventionally
described by either Lennard-Jones (${A}/{r^{12}}$) or Born-Mayer ($A\exp(-Br)$)
forms. Despite their widespread use, these simple functional forms are often
unable to describe the interaction energy accurately over a broad range of
inter-molecular distances, thus creating challenges in the development of ab
initio force fields and potentially leading to decreased accuracy and
transferability. Herein, we derive a novel short-range functional form based on
a simple Slater-like model of overlapping atomic densities and an iterated
stockholder atom (ISA) partitioning of the molecular electron density. We
demonstrate that this Slater-ISA methodology yields a more accurate,
transferable, and robust description of the short-range interactions at minimal
additional computational cost compared to standard Lennard-Jones or Born-Mayer
approaches. Finally, we show how this methodology can be adapted to yield the
standard Born-Mayer functional form while still retaining many of the
advantages of the Slater-ISA approach.
