ParagraphConducting organic materials, such as doped organic polymers, 1 molecular conductors, 2, 3 and emerging coordination polymers, 4 underpin technologies ranging from displays to flexible electronics. 5 Realizing high electrical conductivity in traditionally insulating organic materials necessitates tuning their electronic structure through chemical doping. 6 Furthermore, even materials that are intrinsically conductive, such as single-component molecular conductors, 7,8 require crystallinity for metallic behavior. However, commercial conducting polymers are often purposefully amorphous to aid in durability and processability. 9,10 Using molecular design to engender high conductivity in undoped amorphous materials would enable tunable and robust conductivity in many applications, but there are no intrinsically conducting organic materials which maintain high conductivity when disordered. Here we show that the completely amorphous coordination polymer Ni tetrathiafulvalene tetrathiolate (NiTTFtt) displays intrinsic metallic conductivity. Despite its disordered structure, NiTTFtt exhibits remarkably high electronic conductivity (1280 S/cm) and intrinsically glassy metallic behavior. Analysis with advanced theory shows that these properties are enabled by strong molecular overlap and correlation that are robust to structural perturbations. This unusual set of structural and electronic features results in remarkably stable organic conductivity which is maintained in air for weeks and at temperatures up to 140 °C. Our results demonstrate that molecular design can enable metallic conductivity even in heavily disordered materials. This both raises fundamental questions about how band-like transport can exist in the absence of periodic structure as well as suggests exciting new applications for these materials.
Conducting organic materials, such as doped organic polymers, (1) molecular conductors, (2,3) and emerging coordination polymers, (4) underpin technologies ranging from displays to flexible electronics. (5) Realizing high electrical conductivity in traditionally insulating organic materials necessitates tuning their electronic structure through chemical doping. (6) Furthermore, even materials that are intrinsically conductive, such as single-component molecular conductors, (7,8) require crystallinity for metallic behavior. However, commercial conducting polymers are often purposefully amorphous to aid in durability and processability. (9,10) Using molecular design to engender high conductivity in undoped amorphous materials would enable tunable and robust conductivity in many applications, but there are no intrinsically conducting organic materials which maintain high conductivity when disordered. Here we show that the completely amorphous coordination polymer Ni tetrathiafulvalene tetrathiolate (NiTTFtt) displays intrinsic metallic conductivity. Despite its disordered structure, NiTTFtt exhibits remarkably high electronic conductivity (1280 S/cm) and intrinsically glassy metallic behavior. Analysis with advanced theory shows that these properties are enabled by strong molecular overlap and correlation that are robust to structural perturbations. This unusual set of structural and electronic features results in remarkably stable organic conductivity which is maintained in air for weeks and at temperatures up to 140 °C. Our results demonstrate that molecular design can enable metallic conductivity even in heavily disordered materials. This both raises fundamental questions about how band-like transport can exist in the absence of periodic structure as well as suggests exciting new applications for these materials.
Correlation-driven phenomena in molecular periodic systems are challenging to predict computationally not only because such systems are periodically infinite but also because they are typically strongly correlated. Here, we generalize the variational two-electron reduced density matrix (2-RDM) theory to compute the energies and properties of strongly correlated periodic systems. The 2-RDM of the unit cell is directly computed subject to necessary N-representability conditions such that the unit-cell 2-RDM represents at least one N-electron density matrix. Two canonical but non-trivial systems, periodic metallic hydrogen chains and periodic acenes, are treated to demonstrate the methodology. We show that while single-reference correlation theories do not capture the strong (static) correlation effects in either of these molecular systems, the periodic variational 2-RDM theory predicts the Mott metal-to-insulator transition in the hydrogen chains and the length-dependent polyradical formation in acenes. For both hydrogen chains and acenes, the periodic calculations are compared with previous non-periodic calculations with the results showing a significant change in energies and increase in the electron correlation from the periodic boundary conditions. The 2-RDM theory, which allows for much larger active spaces than are traditionally possible, is applicable to studying correlation-driven phenomena in general periodic molecular solids and materials.
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