# Exponential Relationships Capturing Atomistic Short-Range Repulsion from the Interacting Quantum Atoms (IQA) Method

journal contribution

posted on 15.11.2016, 00:00 by Alex L. Wilson, Paul L. A. PopelierA topological atom
is a quantum object with a well-defined intra-atomic
energy, which includes kinetic energy, Coulomb energy, and exchange
energy. In the context of intermolecular interactions, this intra-atomic
energy is calculated from supermolecular wave functions, by using
the topological partitioning. This partitioning is parameter-free
and invokes only the electron density to obtain the topological atoms.
In this work, no perturbation theory is used; instead, a single wave
function describes the behavior of all van der Waals complexes studied.
As the monomers approach each other, frontier atoms deform, which
can be monitored through a change in their shape and volume. Here
we show that the corresponding atomic deformation energy is very well
described by an exponential function, which matches the well-known
Buckingham repulsive potential. Moreover, we recover a combination
rule that enables the interatomic repulsion energy between topological
atoms A and B to be expressed as a function of the interatomic repulsion
energy between A and A on one hand, and between B and B on the other
hand. As a result a link is established between quantum topological
atomic energies and classical well-known interatomic repulsive potentials.