Structure and electronic structure of Metal-Organic Frameworks within the Density-Functional based Tight-Binding method

TL;DR

This paper develops and validates a SCC-DFTB computational method tailored for large Metal-Organic Frameworks, enabling efficient and accurate structural and electronic property predictions for MOFs with complex metal centers.

Contribution

The paper introduces a validated SCC-DFTB approach specifically adapted for MOFs with Cu, Zn, and Al centers, demonstrating high accuracy in structural and adsorption energy calculations.

Findings

SCC-DFTB predicts MOF structures with less than 5% deviation.

Adsorption energies differ by 12 kJ mol-1 or less from DFT benchmarks.

Method enables efficient modeling of large MOFs with complex metal centers.

Abstract

Density-functional based tight-binding is a powerful method to describe large molecules and materials. Metal-Organic Frameworks (MOFs), materials with interesting catalytic properties and with very large surface areas have been developed and have become commercially available. Unit cells of MOFs typically include hundreds of atoms, which make the application of standard Density-Functional methods computationally very expensive, sometimes even unfeasible. The aim of this paper is to prepare and to validate the Self-Consistent Charge Density-Functional based Tight Binding (SCC-DFTB) method for MOFs containing Cu, Zn and Al metal centers. The method has been validated against full hybrid density-functional calculations for model clusters, against gradient corrected density-functional calculations for supercells, and against experiment. Moreover, the modular concept of MOF chemistry has been discussed on the basis of their electronic properties. We concentrate on MOFs comprising three common connector units: copper paddlewheels (HKUST-1), zinc oxide Zn4O tetrahedron (MOF-5, MOF-177, DUT-6 (MOF-205)) and aluminium oxide AlO4(OH)2 octahedron (MIL-53). We show that SCC-DFTB predicts structural parameters with a very good accuracy (with less than 5% deviation, even for adsorbed CO and H2O on HKUST-1), while adsorption energies differ by 12 kJ mol-1 or less for CO and water compared to DFT benchmark calculations.