Physical Nature of Differential Spin-State Stabilization of Carbenes by Hydrogen and Halogen Bonding: A Domain-Based Pair Natural Orbital Coupled Cluster Study.

The variation in the singlet-triplet energy gap of diphenylcarbene (DPC) upon interaction with hydrogen (water and methanol) or halogen bond (XCF, X = Cl, Br, I) donors to form van der Waals (vdW) complexes is investigated in relation to the electrostatic and dispersion components of such intermolecular interactions. The domain-based local pair natural orbital coupled cluster method, DLPNO-CCSD(T), is used for calculating accurate single-triplet energy gaps and interaction energies for both spin states. The local energy decomposition scheme is used to provide an accurate quantification to the various interaction energy components at the DLPNO-CCSD(T) level.

Accurate Spin-State Energetics for Aryl Carbenes.

A test set of 12 aryl carbenes (AC12) is compiled with the purpose of establishing their adiabatic singlet-triplet energy splittings using correlated wave function based methods. The set covers both singlet and triplet ground state aryl carbenes, as well as a range of magnitudes for the ground state to excited state gap. The performance of coupled cluster methods is examined with respect to the reference wave function, the basis set, and a number of additional methodological parameters that enter the calculation.