Coordination-driven magic numbers in protonated argon clusters

TL;DR

This paper explains the origin of magic numbers in protonated argon clusters by combining quantum Monte Carlo methods with ab initio potentials, revealing structural transitions and the role of many-body interactions.

Contribution

It introduces a novel approach using quantum Monte Carlo and ab initio potentials to understand the structural stability and magic numbers in protonated argon clusters.

Findings

Argon atoms are localized around the classical minimum, showing rigidity.

A structural transition occurs with increasing cluster size.

Many-body coordination influences stability more than two-body interactions.

Abstract

The structural properties of rare-gas clusters can be primarily described by a simple sphere packing model or by pairwise interactions. Remarkably, adding a single proton yields a large set of magic numbers that has remained unexplained. In this Letter, we unravel their origin by combining quantum Monte Carlo techniques with many-body ab initio potentials that correctly capture the proton's coordination environment. Thanks to this approach, we find that argon atoms are mainly localized around the classical minimum, resulting in a particularly rigid behavior in stark contrast to lighter rare-gas clusters. Moreover, as cluster size increases, we identify a clear structural transition from many-body coordination-driven stability to a regime dominated by two-body interactions, reflecting a reshaping of the underlying potential energy landscape.