Intermolecular Interactions

Noncovalent interactions (hydrogen bonds, metal–solvent coordination, dispersion forces, carbene reactivity) shape condensed-phase chemistry and have long been a test for DFT, especially when fragments are open-shell. Errors in the underlying density propagate into interaction energies, so even reasonable functionals are unreliable in these regimes.

In a JCP paper (Joshi, Voora) we introduced perturbative singles corrections (RPAS) to the random-phase approximation. RPAS improves interaction energies across hydrogen-bonding, metal–solvent, carbene–solvent, and dispersion regimes, with the biggest gains in the open-shell cases that have been hardest for post-Kohn–Sham methods. The broader interest is in many-body methods that stay dependable for realistic, multi-reference, and weakly bound systems.