Halogenated Metal–Organic Frameworks for Entangled Photon Pair Generation

Metal–organic frameworks (MOFs), crystalline networks of metal nodes and organic linkers, have been shown to display nonlinear optical (NLO) capabilities for important quantum processes like spontaneous parametric down-conversion (SPDC) and second-harmonic generation (SHG). Experimental and ab initio computational efforts to characterize the NLO properties of MOFs are still in their infancy. The design space of MOFs is substantial, considering all possible combinations of nodes, linkers, topologies, and functional groups that can compose the crystal. We applied ab initio techniques to understand the relationship between MOF chemistry and entangled photon generation by simulating the MOF MIRO-101 with halogenated functional groups. We calculated dielectric and second-order susceptibility tensors in CRYSTAL to obtain the ordinary and extraordinary refractive indices (no and ne), Sellmeier coefficients, phase matching angle, effective nonlinear coefficient (deff), and photon pair correlation time (τc). We further investigated HOMO/LUMO frontier orbitals in functionalized linkers to understand electron distribution as a function of linker chemistry and orientation. This work lays the foundation for a wider exploration of MOFs as candidate quantum optics systems by identifying top-performing materials from large libraries of theoretical structures.