Rodrigo Araujo Mendes

In this work, we present a systematic investigation of the ground- and excited-states of six anionic sulfonated azo dyes with broad applications in the textile industry: Allura Red, Amaranth, Carmoisine, Ponceau, Red 2G, and Sunset Yellow. Ground-state properties were evaluated using density functional theory (DFT) at the $\omega$B97X-D4/ma-def2-SVP level of theory. To identify the most suitable functional for excited-state calculations and to assess vertical excitation energies to low-lying excited-states, we tested a series of hybrid, meta-hybrid, and range-separated hybrid functionals from Jacob's ladder using the Tamm-Dancoff approximation (TDA) and the ma-def2-SVP basis set and compared to results from RI-CC2 and STEOM-DLPNO-CCSD approaches. excited-state properties were then further examined using TDA at the CAM-B3LYP//$\omega$B97X-D4/ma-def2-SVP level of theory. Additionally, the quantum theory of atoms in molecules (QTAIM) was applied to explore density-related properties in both ground and excited-states. We found, perhaps not surprisingly, that excitation weakens the \ce{N=N} bond in both the enol and keto forms of the dyes, but with variations depending on the molecule, conformer, and electronic state.

Hybrid density functional approximations are among the most widely used electronic-structure methods, yet the physical origin of their representation of correlation effects remains incompletely understood. In this work, we analyze correlation in hybrid functionals from the perspectives of Kohn–Sham exchange–correlation potentials, correlated densities, and energy-related observables. We show that the dominant qualitative features of correlation in hybrid DFAs do not arise primarily from the semilocal correlation functional itself, but instead from the difference between the semilocal exchange and exact-exchange contributions. This exchange-difference term is essential for restoring the physically correct structure of the correlation component of the exchange–correlation potential and the corresponding correlated density, whereas the semilocal correlation part acts mainly as a compensating contribution in the core and valence regions. Based on this analysis, we propose an interpretable construction principle for hybrid functionals in which the semilocal/exact-exchange difference is scaled in a controlled way. As a proof of concept, this methodology yields the simple global hybrid UMK26 functional. Despite its uncomplicated global-hybrid form, the functional produces correlation potentials and correlated densities in good agreement with CCSD(T) references, delivers accurate ionization potentials from orbital energies, and yields very good charge-transfer excitation energies, performing on a comparable footing with several recently proposed range-separated hybrids. Although UMK26 is not uniformly optimal across all thermochemical benchmarks, it performs particularly well for self-interaction-sensitive systems and provides a physically transparent route for the rational design of future hybrid density functionals.

This work is the second in the series "On the performance of QTP functionals applied to second-order response properties." In the first paper (J. Chem. Phys. 2025, 162, 054105), we demonstrated the good performance of Quantum Theory Project functionals in predicting static perturbed second-order properties, such as static polarizabilities, nuclear magnetic resonance (NMR) spin-spin coupling constants, and NMR chemical shifts. In the present study, we focus on frequency-dependent properties, namely dynamic polarizabilities and C₆ dispersion coefficients. For completeness, a total of 25 exchange-correlation (XC) functionals were investigated. Dynamic polarizabilities were evaluated at five different perturbation wavelengths: 632.99, 594.10, 543.52, 514.50, and 325.13 nm. This property was also computed using HF, LR-CC3, and EOM-CCSD. In general, EOM-CCSD results are very close to those obtained with linear-response CC3, except at the highest frequency. Among Kohn-Sham calculations, TPSS0 and QTP01 showed the best overall performance for dynamic polarizabilities. We also assessed how well QTP functionals reproduce the pole structure of the CO molecule. For the C₆ dispersion coefficients, calculations were performed using the Casimir-Polder equation. The best overall performance was obtained with O3LYP; however, the first 11 ranked functionals show very similar accuracy. Within the QTP family, QTP01 and LC-QTP provide the best results for C₆ coefficients.

Charge-carrier transport engineering in Zn( ii ) Schiff base coordination compounds yields low-trap and solution-processed fluorescent OLEDs with EQE above 5%.

Correlated Orbital Theory (COT) provides an exact one-particle framework by imposing rigorous physical constraints on Kohn–Sham eigenvalues and, as a consequence, directly incorporates essential electron correlation into molecular orbitals. This approach paves the way toward a new class of approximations within Kohn–Sham Density Functional Theory (KS-DFT). However, since all existing quantum theory project functionals are derived from CAM-B3LYP, we pose the question: Can COT improve the hybrid versions of different exchange-correlation functionals as well? To that end, we explore two optimization strategies for adjusting the existing parameters within PBE0, TPSS0, and LC-PBE0: (i) the ionization potential condition and (ii) the HOMO–LUMO condition. In this sense, we critically assess how these functionals address the “Devil’s Triangle” of KS-DFT: self-interaction error, integer discontinuity, and one-particle spectra. We further examine how the COT influences the description of two challenging properties, charge transfer and reaction barrier heights. Overall, enforcing both COT conditions systematically enhances the performance of functionals within the PBE family, although the description of reaction barriers still leaves room for improvement.

We present a new exchange–correlation (XC) functional inspired by correlated orbital theory and designed to enhance the accuracy of core-electron ionization energy predictions as measured by x-ray photoelectron spectroscopy. This functional, referred to as cQTP25, differs from other Quantum Theory Project (QTP) functionals by optimizing the range-separation parameters through a targeted restriction of the orbital space to core 1s electrons only. We benchmarked cQTP25 against a diverse set of XC functionals spanning multiple rungs of Jacob’s ladder in Density Functional Theory (DFT). The performance was evaluated primarily using the relation IP1s = −ɛ1s, but for completeness, we also computed core ionization potentials using the ΔDFT method. All calculations accounted for both non-relativistic and relativistic corrections. Overall, within Koopmans’s framework, the QTP functionals perform best, and specifically cQTP25. The exception is the ΔDFT analysis, where M11, ωB97X, and BHandHLYP are more accurate and cQTP25 ranks fourth.

Accurate predictions of ionization potentials and electron affinities are essential for guiding the design of organic photovoltaic materials. In this study, we revisit a set of twenty molecules that have been explored in earlier studies and extend the analysis using our approaches: (1) CC theory in its ionization potentials (IPs)/electron affinities (EAs)-equation-of-motion (EOM)/coupled-cluster singles and doubles (CCSD) forms to offer a direct measure of IPs and EAs and (2) Kohn–Sham density functional theory (DFT) using the QTP family compared to a broad range of exchange–correlation functionals (from simple local density approximation/generalized gradient approximation forms through hybrid and range-separated variants). For consistency with prior calculations, one-shot G0W0 corrections are applied to each QTP result. To reduce the cost of coupled-cluster computations, we also investigate both standard and tailored frozen natural orbital (FNO) truncations. Our results confirm that local and semi-local DFT functionals exhibit significant errors, whereas global hybrids and range-separated hybrids offer improved accuracy. The QTP functionals stand out by matching or exceeding the performance of all other functionals. G0W0 on top of DFT starting points further refines orbital energies, bringing them into close agreement with coupled-cluster results. Tailored FNO truncations preserve coupled-cluster accuracy while reducing the virtual space by nearly half. Timing tests on anthracene demonstrate that QTP00 and G0W0@QTP00 workflows almost achieve coupled-cluster quality predictions in under a day, compared with week-long runtimes for full EA-EOM/CCSD.

Correlated Orbital Theory (COT) provides an exact one-particle framework by imposing rigorous physical constraints on Kohn-Sham eigenvalues and, as a consequence, directly incorporates essential electron correlation into molecular orbitals. This approach paves the way toward a new class of approximations within Kohn–Sham Density Functional Theory (KS-DFT). However, since all existing Quantum Theory Project (QTP) functionals are derived from CAM-B3LYP, we pose the question: Can COT improve the hybrid versions of different exchange-correlation (XC) functionals as well? To that end, we explore two optimization strategies for adjusting the existing parameters within PBE0, TPSS0, and LC-PBE0: i) the ionization potential (IP) condition and ii) the HOMO–LUMO condition. In this sense, we critically assess how these functionals address the "Devil's Triangle" of KS-DFT: self-interaction error, integer discontinuity, and one-particle spectra. We further examine how the COT influences the description of two challenging properties, charge transfer and reaction barrier heights. Overall, enforcing both COT conditions systematically enhances the performance of functionals within the PBE family, although the description of reaction barriers still leaves room for improvement.

In this work, we present a systematic investigation of the ground- and excited states of six sulfonated azo dyes with broad applications in the textile industry: Allura Red, Amaranth, Carmoisine, Ponceau, Red 2G, and Sunset Yellow. Ground-state properties were evaluated using density functional theory (DFT) at the ωB97X-D4/ma-def2-SVP level of theory. To identify the most suitable functional for excited-state calculations and to assess vertical excitation energies to low-lying excited states, we tested a series of hybrid, meta-hybrid, and range-separated hybrid functionals from Jacob’s ladder using the Tamm-Dancoff approximation (TDA) and the ma-def2-SVP basis set and compared to results from RI-CC2 and STEOM-DLPNO-CCSD approaches. Excited-state properties were then further examined using TDA at the CAM-B3LYP//ωB97X-D4/ma-def2-SVP level of theory. Additionally, the quantum theory of atoms in molecules (QTAIM) was applied to explore density-related properties in both ground and excited states. We found, perhaps not surprisingly, that excitation weakens the N−−N bond in both the enol and keto forms of the dyes, but with variations depending on the molecule, conformer, and electronic state. This bond weakening, as reflected by changes in electron density descriptors, suggests a possible route for photodegradation in aquatic environments.