Dynamical strengthening of covalent and non-covalent molecular interactions by nuclear quantum effects at finite temperature

Nuclear quantum effects (NQE) tend to generate delocalized dynamics due to the inclusion of the zero-point energy and its coupling to interatomic interactions' anharmonicities.[1] Here, we present evidence that NQE often enhance electronic interactions and can result in dynamical molecular stabilization at finite temperature. The underlying physical mechanism promoted by NQE depends on the particular system under consideration. First, the effective reduction of interatomic distances between functional groups within a molecule can enhance the n → π* interaction by increasing the overlap between molecular orbitals. Second, NQE can localize methyl rotors by temporarily changing molecular bond orders and leading to the emergence of localized transient states. Third, the nuclear quantum dilation induced by the NQE increases the molecular polarizability which hence results in a strengthening of van der Waals interactions.[1] The implications of these boosted interactions include counterintuitive hydroxyl–hydroxyl bonding, hindered methyl rotor dynamics, stronger molecule-surface interactions, and molecular stiffening which generates smoother free-energy surfaces. Our findings yield new insights into the paramount role of nuclear quantum fluctuations in molecules and materials.