Long-Range Repulsion Between Spatially Confined van der Waals Dimers

TL;DR

This paper reveals that van der Waals interactions between spatially confined dimers can become repulsive, contrasting the traditional attractive nature, due to Coulomb interactions in reduced-dimensional environments.

Contribution

It demonstrates that spatial confinement can induce long-range repulsion in vdW dimers, a novel insight supported by analytic calculations and relevant for nanoscale systems.

Findings

Long-range vdW interactions can be repulsive under confinement.

Analytic models show Coulomb interactions cause repulsion.

Relevance to nanoscale surface phenomena and experiments.

Abstract

It is an undisputed textbook fact that non-retarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial dimensionality. The universality of vdW attraction is attributed to the dipolar coupling between fluctuating electron charge densities. Here we demonstrate that the long-range interaction between \textit{spatially confined} vdW dimers becomes repulsive when accounting for the full Coulomb interaction between charge fluctuations. Our analytic results are obtained by using the Coulomb potential as a perturbation over dipole-correlated states for two quantum harmonic oscillators embedded in spaces with reduced dimensionality, however the long-range repulsion is expected to be a general phenomenon for spatially-confined quantum systems. We suggest optical experiments to test our predictions, analyze their relevance in the context of intermolecular interactions in nanoscale environments, and rationalize the recent observation of anomalously strong screening of the lateral vdW interactions between aromatic hydrocarbons adsorbed on metal surfaces.