Inverse Surface Melting in Confined Clusters:  Ar₁₃in Zeolite L

Abstract

Monte Carlo and molecular dynamics simulations on an Ar 13 cluster in zeolite L have been carried out at a series of temperatures to understand the rigid-nonrigid transition corresponding to the solid-liquid transition exhibited by the free Ar 13 cluster. The icosahedral geometry of the free cluster is no longer preferred when the cluster is confined in the zeolite. The root-mean-squared pair distance fluctuation, δ, exhibits a sharp, well-defined rigid-nonrigid transition at 17 K as compared to 27 K for the free cluster. Multiple peaks in the distribution of short-time averages of the guest-host interaction energy indicate coexistence of two phases. It is shown that this transition is associated with the inner atoms becoming mobile at 17 K even while the outer layer atoms, which are in close proximity to the zeolitic wall, continue to be comparatively immobile. This may be contrasted with the melting of large free clusters of 40 or more atoms which exhibit surface melting. Guest-host interactions seem to play a predominant role in determining the properties of confined clusters. We demonstrate that the volume of the cluster increases rather sharply at 17 and 27 K respectively for the confined and the free cluster. Power spectra suggest that the motion of the inner atoms is generally parallel to the atoms which form the cage wall.

Size-dependent melting of nanoparticles: Hundred years of thermodynamic model

“…This is attributed to the suppression of vibrational motion of the surface atoms by the interface epitaxy. The melting starts from the centre and proceeds towards the surface [114] for embedded nanoparticles, while the melting starts from the surface and proceeds towards the centre for free nanoparticles.…”

Effect of confinement in the α-cages of zeolite NaCaA on the properties of Ar13 cluster: A Monte Carlo study

“…This suggests that the confining medium, in this case, zeolite NaCaA, has a strong influence on the width of these peaks. Elsewhere it is shown that the increase in the volume of a free cluster with increase in temperature is larger than that for a confined cluster above 29 K (Chitra and Yashonath 1997).…”

Monte Carlo and molecular dynamics simulation of argon clusters andn-alkanes in the confined regions of zeolites

“…This suggests that the confined cluster spends a larger fraction of time on the saddle points in the potential energy surface as compared to the free cluster. Earlier work on Am3 cluster in the zeolite L has shown that such a cluster will exhibit the phenomenon of inverse surface melting: the inner atoms of the confined Arn3 cluster melt (acquire mobility) even before the outer atoms melt (Chitra and Yashonath 1997). This is in contrast to the surface melting behaviour exhibited by free clusters of medium to large size, where atoms on the outer surface usually melt before the inner core acquires mobility (Cheng and Berry 1992;Kunz and Berry 1993).…”