Regular Article

Questioning the structure of Sr⁺Ar_n clusters^★

¹ University Grenoble Alpes, LiPhy, and CNRS, LiPhy, 38000 Grenoble, France
² Laboratoire de Physique Quantique, Faculté des Sciences de Monastir, Avenue de l’Environnement 5019, Monastir, Tunisia
³ University of Jeddah, Faculty of Science, Physics Department, Jeddah, Kingdom of Saudi Arabia

^a e-mail: florent.calvo@univ-grenoble-alpes.fr

Received: 5 April 2018
Received in final form: 29 May 2018
Published online: 2 August 2018

Abstract

The stable structures of argon clusters doped with a strontium cation were computationally determined using a many-body polarizable potential fitted to reproduce highly accurate electronic structure calculations at the coupled cluster level of theory. The basin-hopping global optimization method was employed to locate putative lowest energy structures of Sr⁺Ar_n clusters with n < 160, and the effects of zero-point energy corrections and of possible entropy-driven structural transitions were accounted for in the (quantum) harmonic approximation. The results suggest an overall icosahedral growth pattern over the investigated size range, with the strontium cation being generally twelvefold coordinated by argon atoms also arranged into an icosahedron. However, the strain between the first coordination shell and the remaining cluster is significant, with the cation not always residing at the center of the cluster despite being much more strongly bound. As a result, non-icosahedral coordination shells are also occasionally found with local decahedral or cubic arrangements. This structural diversity could explain the relative discrepancies with existing mass spectrometry abundances.