Loading...
Derniers dépôts, tout type de documents
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.
We performed several types of ab initio calculations, from Hartree-Fock to Complete-Active-Space second-order perturbation theory and Coupled Cluster, on compact clusters of stoichiometry XY, where X and Y are atoms belonging to the second row of the periodic table. More precisely, we considered the “cubic” structures of three isoelectronic groups, having a total of 48, 52, and 56-electrons, respectively. Notice that the highly symmetric cubic clusters of type X are characterized by an symmetry group, while the XY structures, with XY, have at most a symmetry. Binding energies and wave function analysis of these clusters have been performed, in order to investigate the nature, and the electron delocalization of these systems and establish a comparison between them. To this purpose, we also computed the Total-Position Spread tensor for each structure, a quantity which is related to the multi-reference nature of a system wave function.
Methyl-p-benzoquinone (MpBQ, CH3C6H3(═O)2) is a prototypical molecule in the study of quinones, which are compounds of relevance in biology and several redox reactions. Understanding the electron attachment properties of MpBQ and its ability to form anions is crucial in elucidating its role in these reactions. In this study, we investigate electron attachment to MpBQ employing a crossed electron-molecular beam experiment in the electron energy range of approximately 0 to 12 eV, as well as theoretical approaches using quantum chemical and electron scattering calculations. Six anionic species were identified: C7H6O2–, C7H5O2–, C6H5O–, C4HO–, C2H2–, and O–. The parent anion is formed most efficiently, with large cross sections, through two resonances at electron energies between 1 and 2 eV. Potential reaction pathways for all negative ions observed are explored, and the experimental appearance energies are compared with calculated thermochemical thresholds. Although exhibiting similar electron attachment properties to pBQ, MpBQ’s additional methyl group introduces entirely new dissociative reactions, while quenching others, underscoring its distinctive chemical behavior.
To expand the QUEST database of highly accurate vertical transition energies, we consider a series of large organic chromogens ubiquitous in dye chemistry, such as anthraquinone, azobenzene, BODIPY, and naphthalimide. We compute, at the CC3 level of theory, the singlet and triplet vertical transition energies associated with the low-lying excited states. This leads to a collection of more than 120 new highly accurate excitation energies. For several singlet transitions, we have been able to determine CCSDT transition energies with a compact basis set, finding minimal deviations from the CC3 values for most states. Subsequently, we employ these reference values to benchmark a series of lower-order wave function approaches, including the popular ADC(2) and CC2 schemes, as well as time-dependent density-functional theory (TD-DFT), both with and without applying the Tamm–Dancoff approximation (TDA). At the TD-DFT level, we evaluate a large panel of global, range-separated, local, and double hybrid functionals. Additionally, we assess the performance of the Bethe–Salpeter equation (BSE) formalism relying on both G0W0 and evGW quasiparticle energies evaluated from various starting points. It turns out that CC2 and ADC(2.5) are the most accurate models among those with respective O(N5) and O(N6) scalings with system size. In contrast, CCSD does not outperform CC2. The best performing exchange–correlation functionals include BMK, M06–2X, M06-SX, CAM-B3LYP, ωB97X-D, and LH20t, with average deviations of approximately 0.20 eV or slightly below. Errors on vertical excitation energies can be further reduced by considering double hybrids. Both SOS-ωB88PP86 and SOS-ωPBEPP86 exhibit particularly attractive performances with overall quality on par with CC2, whereas PBE0-DH and PBE-QIDH are only slightly less efficient. BSE/evGW calculations based on Kohn–Sham starting points have been found to be particularly effective for singlet transitions, but much less for their triplet counterparts.
Sujets
Quantum Chemistry
Argile
Polarizabilities
Atrazine
Auto-énergie
Relativistic quantum chemistry
Aimantation
Ion
Rydberg states
Diffusion Monte Carlo
Configuration Interaction
Range separation
Approximation GW
AB-INITIO
Numerical calculations
Mécanique quantique relativiste
Perturbation theory
Ab initio calculation
Atoms
Biodegradation
Atomic processes
Atomic and molecular collisions
Parallel speedup
QSAR
Relativistic corrections
Anderson mechanism
Atomic charges
Carbon Nanotubes
Path integral
Xenon
Chimie quantique
A priori Localization
Dirac equation
Pesticide
A posteriori Localization
New physics
Configuration interactions
Dispersion coefficients
Quantum Monte Carlo
3115ag
Atrazine-cations complexes
Dipole
Electron electric dipole moment
Valence bond
Fonction de Green
Time reversal violation
3115ae
Relativistic quantum mechanics
Chemical concepts
Time-dependent density-functional theory
X-ray spectroscopy
Molecular descriptors
3115vj
Green's function
3315Fm
Coupled cluster calculations
3115vn
Argon
Pesticides Metabolites Clustering Molecular modeling Environmental fate Partial least squares
Atomic data
Spin-orbit interactions
Ground states
Acrolein
3115bw
3115am
Azide Anion
Analytic gradient
Quantum chemistry
États excités
Single-core optimization
AROMATIC-MOLECULES
CIPSI
CP violation
Line formation
Electron correlation
ALGORITHM
Théorie des perturbations
Hyperfine structure
Coupled cluster
Atom
3115aj
BENZENE MOLECULE
BIOMOLECULAR HOMOCHIRALITY
Corrélation électronique
3470+e
Atomic and molecular structure and dynamics
Abiotic degradation
AB-INITIO CALCULATION
Petascale
Wave functions
Electron electric moment
Parity violation
Molecular properties
Atomic charges chemical concepts maximum probability domain population
Excited states
Large systems
Density functional theory
Adiabatic connection
Anharmonic oscillator
Diatomic molecules