Predicting STM-ESR Detectability of Adsorbed Transition-Metal Phthalocyanines from First Principles

Abstract

Surface-supported transition-metal phthalocyanine (TMPc) complexes provide a promising platform for molecular spintronics, owing to their tunable spin states and well-defined structures. Scanning tunneling microscopy combined with electron spin resonance (STM-ESR) enables the detection and manipulation of single-molecule spins with atomic-scale precision; yet, identifying molecular systems capable of producing detectable STM-ESR signals remains challenging. Here, we establish a predictive simulation framework that integrates density functional theory (DFT) with the hierarchical equations of motion (HEOM) to evaluate spin properties and STM-ESR responses of TMPc molecules adsorbed on MgO/Ag(100). Through systematic analysis of spin-polarized electronic structures, hybridization functions, and singly occupied molecular orbitals governing molecule–substrate hybridization, we find that FePc, MnPc, NiPc, and ScPc retain sufficient spin polarization and hybridization strength to support observable STM-ESR signals, whereas CoPc and CuPc exhibit complete spin quenching upon adsorption. These results clarify how orbital symmetry and molecule–substrate hybridization control spin reorganization in TMPc systems and demonstrate that the proposed DFT+HEOM framework provides a transferable computational strategy for screening surface-supported molecular spin systems with potential STM-ESR activity.