Ab Initio Simulations To Understand the Leaf-Shape Crystal Morphology of ZIF-L with Two-Dimensional Layered Network

Abstract

Two-dimensional porous coordination polymers are the perfect candidates as ultrathin membranes with superior gas separation performances. However, fundamental understanding on the crystal growth, which is vital for membrane applications, is very limited. Studies on the crystal morphologies could provide valuable clues. In this paper, we carried out an ab initio study to understand the crystal morphology of the two-dimensional ZIF-L. Several typical surfaces, such as (001), (100), (010), and (110) surface slabs, were generated by using our developed automated surface generation software package. The corresponding surface energies were calculated. Our results show that the surface relaxation is localized in the first Zn layer, but the magnitude of energy reduction is quite significant, about 60% of surface energy of the as-cut surfaces. We identified two important factors that determine the surface energetic orders of different crystal surfaces: number density and the types of dangling bonds. Particularly, ...