Ab Initio Molecular Dynamic Simulations on Pd Clusters Confined in UiO-66-NH2

Abstract

The thermodynamically stable metal organic framework UiO-66-NH2 has experimentally been demonstrated as an ideal platform to isolate metal clusters within its nanocages; however, the electronic structures and the dynamics of the encapsulated metal clusters are still unclear. Ab initio molecular dynamics simulations combined with density functional theory-based methods were employed to search the stable structures of Pdn@UiO-66-NH2 composites, and their electronic properties were analyzed in detail. We found that the thermodynamics of the composites are highly correlated with charge transfer between the Pdn cluster and the UiO-66-NH2 framework, as well as the deformation energy of the framework. In addition, both ab initio molecular dynamics simulations and density functional theory calculations show that the small Pd clusters can easily diffuse into the tetrahedral cage of UiO-66-NH2 from the octahedral cage through the window connecting these two types of cages, with a small energy barrier.