van der Waals Interactions in Confined Spaces: Surprises Beyond the Random-Phase Approximation

The confinement of molecules is ubiquitous in realistic systems relevant to sensing, catalysis, energy materials or biophysics. The accurate description of such systems thus requires a deep understanding of intermolecular interactions under confinement. van der Waals (vdW) dispersion thereby represents a crucial part. vdW forces arise from Coulomb-coupled quantum-mechanical fluctuations in the electron density. However, the treatment of practically-relevant systems typically relies on the interatomic dipole limit or random-phase approximation (RPA), thus failing to capture the full complexity of vdW dispersion. We here present a consistent methodology to incorporate so-called dipole-correlated Coulomb singles (DCS) into an efficient many-body treatment of vdW forces through a perturbation expansion over the dipole-coupled state of the Many-Body Dispersion (MBD) model. DCS include so-far neglected beyond-dipolar correlation and dispersion-polarization terms beyond the RPA. Combining hybrid density-functional approximations with MBD+DCS yields high-accuracy binding energies for supramolecular complexes at low computational costs. In more complex environments, DCS can alter long-range interactions even qualitatively, which may allow to explain several puzzling experimental findings.