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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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In a recent letter [Phys. Rev. Lett. 131, 216401] we presented the multichannel Dyson equation (MCDE) in which two or more many-body Green's functions are coupled. In this work we will give further details of the MCDE approach. In particular we will discuss: 1) the derivation of the MCDE and the definition of the space in which it is to be solved; 2) the rationale of the approximation to the multichannel self-energy; 3) a diagrammatic analysis of the MCDE; 4) the recasting of the MCDE on an eigenvalue problem with an effective Hamiltonian that can be solved using standard numerical techniques. This work mainly focuses on the coupling between the one-body Green's function and the three-body Green's function to describe photoemission spectra, but the MCDE method can be generalized to the coupling of other many-body Green's functions and to other spectroscopies.

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Galvinoxyl, as one of the most extensively studied organic stable free radicals, exhibits a notable phase transition from a high-temperature (HT) phase with a ferromagnetic (FM) intermolecular interaction to a low-temperature (LT) phase with an antiferromagnetic (AFM) coupling at 85 K. Despite significant research efforts, the crystal structure of the AFM LT phase has remained elusive. This study successfully elucidates the crystal structure of the LT phase, which belongs to the P[1 with combining macron] space group. The crystal structure of the LT phase is found to consist of a distorted dimer, wherein the distortion arises from the formation of short intermolecular distances between anti-node carbons in the singly-occupied molecular orbital (SOMO). Starting from the structure of the LT phase, wave function calculations show that the AFM coupling 2J/kB varies significantly from −1069 K to −54 K due to a parallel shift of the molecular planes within the dimer.

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Sujets

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

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