Abstract
Finite-temperature behaviour of a hollow golden cage (HGC) plays a crucialrole in its potential applications as a catalyst, drug delivery agent, contrasting agent and so on. This physico-chemical property of HGCs is not well understood so far. In that context, Born–Oppenheimer molecular dynamics (BOMD) simulations are performed on a well-known ‘free-standing’ HGC. The cluster considered in this study is the ground state Au18 cluster (a cage with a diameter of about >5.5 Å). The results thus obtained are compared with the BOMD simulation results reported earlier on Au32 icosahedron cage, a conformation with a diameter of nearly. The sphericity of both the clusters is studied using a shape deformation parameter as a function of time and temperature. These results are supplemented by radial distribution function at various temperatures. The observations and analysis of results indicate that, both the clusters retain an HGC conformation from 300 to 400 K, admitting structural fluxionality by the Au18 cluster. Remarkably, the Au18 cluster is able to maintain its hollowness and sphericity up to a high temperature of 1000 K. Underlying structural and electronic properties influencing the individualistic behaviour of cages are highlighted. Composition of the frontier molecular orbitals and the charge distribution play a crucial role in the finite-temperature behaviour of the Au cages. The conclusions are supplemented by supporting calculations on another degenerate ground state Au18 hollow cage and a well-known pyramidal Au18 cage at 300 and 400 K.
Acknowledgements
The authors dedicate this work to Prof. Sourav Pal in honour of his 60th birthday. The authors acknowledge the Center of Excellence in Scientific Computing (CoESC) at CSIR-NCL, Pune and CSIR-Fourth Paradigm Institute, Bangalore for providing access to their high performance computing facilities. The authors also acknowledge a grant from MSM: CSC-0129 project.
Disclosure statement
No potential conflict of interest was reported by the authors.
Supplemental data
Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00268976.2015.1062151.