First Principles Studies of Gas Adsorption in Metal Organic Frameworks.

摘要

This thesis focuses on using theoretical and computational techniques to study gas absorption in metal organic frameworks (MOFs). The ultimate goal of these studies is to establish a methodology capable of computing the gas loading behavior of MOFs with minimal empirical inputs. We are also dedicated to understanding the underlying physics of guest-framework interactions, so general guidelines can be provided to design MOFs with better gas adsorption performance.;In this thesis, we will investigate two classes of MOFs, namely those with and without open metal sites. MOFs with coordinatively saturated metal centers are dominated by weak nonbonding interactions between the guest molecules and the organic ligands. Therefore, a consistent set of force field parameters will be developed for both guest molecules and frameworks based on first principles calculations. Utilizing symmetry adapted perturbation theory (SAPT), we decompose the interaction energies into distinct physical meaningful terms, which then be fit with physically motivated functional forms. We will show that the resulting first principles potential is extraordinary accurate, and is transferrable across different chemical environments. In addition, we will develop a novel algorithm which will accelerate our simulations by several orders of magnitude, thus enabling us to conduct large-scale structure screening. The aforementioned techniques will be used to investigate the cooperative synergistic effects between different types of organic ligands, an important industrial-relevant problem.;In contrast to the first class of MOFs, the loading isotherms of systems with open metal centers are largely controlled by several strong binding sites, in which perturbation theory generally fails to converge. Consequently, instead of the SAPT-based techniques, we will study these systems using density functional theory (DFT) methods. We will illustrate the effect of flue gas contaminants on the metal centers, an important concern for this class of MOFs in industrial application. Finally, we will explore the physical properties of the open-metal binding sites by studying the IR spectrum of the adsorbed molecules.;Though all these studies, we are able to establish a deep understanding to the MOF gas adsorption behavior, and we will illustrate the advantages of computer simulation techniques in this area.