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Excited-state absorption (ESA) corresponds to the transition between two electronic excited states and is a fundamental process for probing and understanding light-matter interactions. Accurate modeling of ESA is indeed often required to interpret time-resolved experiments. In this contribution, we present a dataset of 53 ESA oscillator strengths in three different gauges and the associated vertical transition energies between 71 excited states of 23 small- and medium-sized molecules from the QUEST database. The reference values were obtained within the quadratic-response (QR) CC3 formalism using eight different Dunning basis sets. We found that the d-aug-cc-pVTZ basis set is always adequate while its more compact double-$\zeta$ counterpart, d-aug-cc-pVDZ, performs well in most applications. These QR-CC3 data allow us to assess the performance of QR-TDDFT, with and without applying the Tamm-Dancoff approximation, using a panel of global and range-separated hybrids (B3LYP, BH{\&}HLYP, CAM-B3LYP, LC-BLYP33, and LC-BLYP47), as well as several lower-order wavefunction methods, i.e., QR-CCSD, QR-CC2, EOM-CCSD, ISR-ADC(2), and ISR-ADC(3). We show that QR-TDDFT delivers acceptable errors for ESA oscillator strengths, with CAM-B3LYP showing particular promise, especially for the largest molecules of our set. We also find that ISR-ADC(3) exhibits excellent performance

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Building on our recent study [https://doi.org/10.1021/acs.jpclett.3c02052, J. Phys. Chem. Lett. 14, 8780 (2023)], we explore the generalization of the ground-state Kohn-Sham (KS) formalism of density-functional theory (DFT) to the (singlet) excited states of the asymmetric Hubbard dimer at half-filling. While we found that the KS-DFT framework can be straightforwardly generalized to the highest-lying doubly-excited state, the treatment of the first excited state presents significant challenges. Specifically, using a density-fixed adiabatic connection, we show that the density of the first excited state lacks non-interacting $v$-representability. However, by employing an analytic continuation of the adiabatic path, we demonstrate that the density of the first excited state can be generated by a complex-valued external potential in the non-interacting case. More practically, by performing state-specific KS calculations with exact and approximate correlation functionals -- each state possessing a distinct correlation functional -- we observe that spurious stationary solutions of the KS equations may arise due to the approximate nature of the functional.

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Reduced density matrix functional theory (RDMFT) and coupled cluster theory restricted to paired double excitations (pCCD) are emerging as efficient methodologies for accounting for the so-called non-dynamic electronic correlation effects. Up to now, molecular calculations have been performed with real-valued orbitals. However, before extending the applicability of these methodologies to extended systems, where Bloch states are employed, the subtleties of working with complex-valued orbitals and the consequences of imposing time-reversal symmetry must be carefully addressed. In this work, we describe the theoretical and practical implications of adopting time-reversal symmetry in RDMFT and pCCD when allowing for complex-valued orbital coefficients. The theoretical considerations primarily affect the optimization algorithms, while the practical implications raise fundamental questions about the stability of solutions. Specifically, we find that complex solutions lower the energy when non-dynamic electronic correlation effects are pronounced. We present numerical examples to illustrate and discuss these instabilities and possible problems introduced by N-representability violations.

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The Bethe-Salpeter equation has been extensively employed to compute the two-body electron-hole propagator and its poles which correspond to the neutral excitation energies of the system. Through a different time-ordering, the two-body Green's function can also describe the propagation of two electrons or two holes. The corresponding poles are the double ionization potentials and double electron affinities of the system. In this work, a Bethe-Salpeter equation for the two-body particle-particle propagator is derived within the linear-response formalism using a pairing field and anomalous propagators. This framework allows us to compute kernels corresponding to different self-energy approximations ($GW$, $T$-matrix, and second-Born) as in the usual electron-hole case. The performance of these various kernels is gauged for singlet and triplet valence double ionization potentials using a set of 23 small molecules. The description of double core hole states is also analyzed.

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Sujets

Single-core optimization CP violation QSAR Relativistic corrections Atoms Atomic charges Configuration Interaction AB-INITIO Xenon Ab initio calculation Diffusion Monte Carlo Atomic data AB-INITIO CALCULATION Chimie quantique Carbon Nanotubes A posteriori Localization Green's function Atrazine-cations complexes Auto-énergie Analytic gradient 3470+e États excités CIPSI Parity violation BENZENE MOLECULE Quantum chemistry Numerical calculations Mécanique quantique relativiste Electron correlation Biodegradation 3115ae Valence bond Atomic processes Time-dependent density-functional theory Relativistic quantum chemistry Azide Anion New physics Adiabatic connection 3115vj 3115ag ALGORITHM Chemical concepts Ion Anderson mechanism Atomic and molecular structure and dynamics Time reversal violation Molecular descriptors Petascale Approximation GW Dipole Pesticide Abiotic degradation Dispersion coefficients Density functional theory 3115vn Configuration interactions Electron electric dipole moment Perturbation theory Atom Rydberg states Théorie des perturbations Wave functions Atrazine Path integral Spin-orbit interactions 3115am Corrélation électronique Dirac equation Atomic charges chemical concepts maximum probability domain population Pesticides Metabolites Clustering Molecular modeling Environmental fate Partial least squares Acrolein A priori Localization X-ray spectroscopy Line formation Electron electric moment AROMATIC-MOLECULES Fonction de Green Hyperfine structure Excited states Molecular properties Relativistic quantum mechanics Quantum Chemistry Parallel speedup 3115bw Argile Ground states Anharmonic oscillator Quantum Monte Carlo Coupled cluster Range separation Aimantation BIOMOLECULAR HOMOCHIRALITY Polarizabilities Coupled cluster calculations Diatomic molecules 3115aj 3315Fm Argon Large systems Atomic and molecular collisions

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