Two-Dimensional Electrically Conductive Metal-Organic Frameworks: Insights and Guidelines from Theory

ConspectusTwo-dimensional (2D) metal-organic frameworks (MOFs) are a new class of multifunctional low-dimensional materials where extended layers of tetra-coordinated metal nodes with electron-rich π-conjugated organic linkers are stacked via van der Waals interactions. With two possible electron transport pathways along the intra- and interlayer directions, many 2D MOFs offer electrical conductivity on top of other known properties of MOFs, which include permanent porosity and exceptionally high surface area, promising unprecedented breakthroughs in producing high-performance and cost-effective materials for batteries, semiconductors, and supercapacitors. To make progress toward these applications, theoretical and computational tools play an essential role in unraveling structure-property-function relationships, identifying materials with tailored electronic properties, and developing design criteria for novel electrically conductive (EC) MOFs yet to be experimentally synthesized and characterized. However, such studies are still in their infancy, hampered by various factors including the high computational cost of simulating these complex extended materials composed of hundreds of atoms.In this Account, we summarize and discuss our group's efforts in mapping out the structure-property-function relationships of EC MOFs while deliberating present and future research on big data analysis and machine learning (ML) for novel materials discovery. First, selected examples of these electrically conductive materials will be discussed. We will present quantum mechanical calculations deciphering their thermodynamic stability, electronic structure, and photochemical reactivity. Second, to help the community move beyond selected studies of these materials, we introduce our EC-MOF Database. It is the only database solely dedicated to EC MOFs, which provides not only the crystal structures but also the electronic properties of 1057 structures calculated at the periodic density functional theory (DFT) level. We then discuss the application of ML techniques to utilize the EC-MOF Database in property predictions in a high-throughput manner. Lastly, we will introduce the flexible nature of these layered materials and discuss how it affects the nature of their electrical conductivity. Selected examples will be discussed to demonstrate the applicability and appropriateness of molecular dynamics (MD) simulations based on high-dimensional neural network potentials (NNPs) compared to the expensive ab initio MD (AIMD) data.The overarching objective of this Account is to bring to attention the computationally-ready crystal structures and the developed ML models and NNPs for EC MOFs so that the broader community can utilize them for further studies. This will also help experimental groups make informed decisions on designing and synthesizing novel EC MOF-based materials. With the possibility of inverse design based on the provided theoretical insights and the research conducted on both fundamental and applied fields, we believe that 2D EC MOFs will attract even more attention in the near future to unlock their full potential for compact electronic device fabrications.