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Yuhan Yang
(Advisor: Prof. David S Sholl)
will defend a doctoral thesis entitled
High throughput methods for prediction of molecular diffusion
in metal-organic frameworks
On
Thursday, June 23 at 1:00 p.m.
Abstract
Metal-organic frameworks (MOFs) are a large group of crystalline nanoporous materials that can play a special role in separation because their monodisperse pore architectures offer potential to precisely control molecular diffusion. Usually, accurate computational approaches to predicting diffusion in microporous materials are time-consuming. This thesis aims to develop highly efficient computational methods that can accurately describe diffusion of diverse sets of molecules in large libraries of MOFs. I developed an efficient method for predicting self-diffusivities in flexible frameworks. A simple correlation between molecular size, average loaded window size, and hopping rate allows the hopping rate of a wide range of spherical molecules to be predicted with just two full calculations. Subsequently, I systematically examined the impact of MOF flexibility on molecular diffusion by building up a diverse dataset of self-diffusivities in MOFs that account for framework flexibility. A descriptor, average loaded window size, was proposed to qualitatively identify when MOF flexibility can be neglected to reduce computational cost. The dataset from this work was further expanded to build a machine learning prototype for predicting molecular diffusivities for arbitrary molecule/framework pairs. Predictions of molecular diffusion in MOFs rely on the accuracy of force fields used for molecular simulations. The generic force field UFF4MOF was found to give unreliable results for the structures of MOFs containing rare-earth species. I proposed an improved force field function to better describe these materials, making it possible to further enrich the diffusion dataset with complex rare earth MOFs. Taken together, this thesis work developed several efficient methods for reliable high throughput calculations of molecular diffusivities in MOFs.
Committee
David S Sholl, ChBE (advisor)
Christopher W Jones, ChBE
Ryan P Lively, ChBE
Andrew J Medford, ChBE
Jesse G McDaniel, Chem
