The binding free energy of hydrogen-bonded complexes is generally inversely proportional to the solvent dielectric constant. This occurs because the solvent-accessible surface area of the complex is always smaller than that of the individual subsystems, leading to a reduction in solvation energy. The present study explores the potential for stabilizing hydrogen-bonded complexes in a solvent with higher polarity. Contrary to the established understanding, we have demonstrated that the hydrogen-bonded complex (CH3CH2COOH⋅⋅⋅2,4,6-trimethylpyridine) can be better stabilized in a solvent with higher polarity. In this case, a significant charge transfer between the subsystems results in an increased dipole moment of the complex, leading to its stabilization in a more polar solvent. The expected inverse relationship between binding free energy and solvent dielectric constant is observed when the charge transfer between the subsystems is low. Thus, the magnitude of the charge transfer between subsystems is possibly the key factor in determining the stabilization or destabilization of H-bonded complexes in different solvents. Here, we present a comprehensive study that combines experimental and theoretical approaches, including nuclear magnetic resonance (NMR), infrared (IR) spectroscopies and quantum chemical calculations to validate the findings.

• Klíčová slova
• Hydrogen bonding, IR, Metadynamics, Micro-solvation, NMR, ONIOM, Solvent effect,
• Publikační typ
• časopisecké články MeSH

The new generation of proposed light-emitting molecules for organic light-emitting diodes (OLEDs) has raised considerable research interest due to its exceptional feature─a negative singlet-triplet (ST) gap violating Hund's multiplicity rule in the excited S1 and T1 states. We investigate the role of spin polarization in the mechanism of ST gap inversion. Spin polarization is associated with doubly excited determinants of certain types, whose presence in the wave function expansion favors the energy of the singlet state more than that of the triplet. Using a perturbation theory-based model for spin polarization, we propose a simple descriptor for prescreening of candidate molecules with negative ST gaps and prove its usefulness for heptazine-type molecules. Numerical results show that the quantitative effect of spin polarization decreases linearly with the increasing highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) exchange integral. Comparison of single- and multireference coupled-cluster predictions of ST gaps shows that the former methods provide good accuracy by correctly balancing the effects of doubly excited determinants and dynamic correlation. We also show that accurate ST gaps may be obtained using a complete active space model supplemented with dynamic correlation from multireference adiabatic connection theory.

• Publikační typ
• časopisecké články MeSH

Community efforts in the computational molecular sciences (CMS) are evolving toward modular, open, and interoperable interfaces that work with existing community codes to provide more functionality and composability than could be achieved with a single program. The Quantum Chemistry Common Driver and Databases (QCDB) project provides such capability through an application programming interface (API) that facilitates interoperability across multiple quantum chemistry software packages. In tandem with the Molecular Sciences Software Institute and their Quantum Chemistry Archive ecosystem, the unique functionalities of several CMS programs are integrated, including CFOUR, GAMESS, NWChem, OpenMM, Psi4, Qcore, TeraChem, and Turbomole, to provide common computational functions, i.e., energy, gradient, and Hessian computations as well as molecular properties such as atomic charges and vibrational frequency analysis. Both standard users and power users benefit from adopting these APIs as they lower the language barrier of input styles and enable a standard layout of variables and data. These designs allow end-to-end interoperable programming of complex computations and provide best practices options by default.

• Publikační typ
• časopisecké články MeSH