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<p>Inverted singlet–triplet (INVEST) materials, characterized by a negative singlet–triplet energy gap (ΔE<sub>ST</sub>), hold great promise for next-generation Organic Light Emitting Diode (OLED) applications. However, their accurate computational description remains challenging, as conventional low-cost methods often fail to capture the subtle electron correlation effects governing the gap inversion. In this work, we present a systematic fine-tuning of the spin-component scaling (SCS) parameters for the second-order coupled cluster (CC2) and Algebraic Diagrammatic Construction (ADC(2)) methods, targeting the accurate prediction of ΔE<sub>ST</sub> in INVEST systems. Using a set of eight triangular-shaped INVEST compounds, we screened opposite- and same-spin SCS parameters against Theoretical Best Estimate (TBE) reference values from Jacquemin and collaborators.[<CitationRef CitationID="CR1">1</CitationRef>] The optimal parameters (c<sub>os</sub> = 1.0, c<sub>ss</sub> = 1.4/1.6 for SCS-CC2/ADC(2)) differ markedly from the conventional ones, demonstrating that reparameterization is essential for a balanced description of the ΔE<sub>ST</sub> in this class of molecules. The spin-component decomposition of the correlation energy allowed deriving a general expression to estimate TBE gaps directly from CCS excitation energies, offering a computationally inexpensive diagnostic tool. Beyond parameter optimization, SCS tuning proved to be a valuable instrument to reveal how electron correlation couples to topology-related features such as electron density redistribution. We also outlined a strategy for extending the SCS tuning to extended INVEST systems. Taken together, these results establish SCS-CC2 and SCS-ADC(2) as cost-effective and physically transparent alternatives to higher-level methods for the study of INVEST photophysics.</p>

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Tuning the spin-component scaling scheme for inverted singlet–triplet (INVEST) systems: improving CC2 and ADC(2) from excited-state energies to topological features

  • 期刊论文

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  • 发表日期：

    2026年7月22日

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  • Gaetano Ricci

摘要

Inverted singlet–triplet (INVEST) materials, characterized by a negative singlet–triplet energy gap (ΔEST), hold great promise for next-generation Organic Light Emitting Diode (OLED) applications. However, their accurate computational description remains challenging, as conventional low-cost methods often fail to capture the subtle electron correlation effects governing the gap inversion. In this work, we present a systematic fine-tuning of the spin-component scaling (SCS) parameters for the second-order coupled cluster (CC2) and Algebraic Diagrammatic Construction (ADC(2)) methods, targeting the accurate prediction of ΔEST in INVEST systems. Using a set of eight triangular-shaped INVEST compounds, we screened opposite- and same-spin SCS parameters against Theoretical Best Estimate (TBE) reference values from Jacquemin and collaborators.[1] The optimal parameters (cos = 1.0, css = 1.4/1.6 for SCS-CC2/ADC(2)) differ markedly from the conventional ones, demonstrating that reparameterization is essential for a balanced description of the ΔEST in this class of molecules. The spin-component decomposition of the correlation energy allowed deriving a general expression to estimate TBE gaps directly from CCS excitation energies, offering a computationally inexpensive diagnostic tool. Beyond parameter optimization, SCS tuning proved to be a valuable instrument to reveal how electron correlation couples to topology-related features such as electron density redistribution. We also outlined a strategy for extending the SCS tuning to extended INVEST systems. Taken together, these results establish SCS-CC2 and SCS-ADC(2) as cost-effective and physically transparent alternatives to higher-level methods for the study of INVEST photophysics.