  Intermolecular bonds are weak compared to covalent bonds, but they are strong
enough to influence the properties of large molecular systems. In this work, we
investigate how strong light-matter coupling inside an optical cavity can
modify these intermolecular forces. We perform a detailed comparison between
currently available ab initio electron-photon methodologies. The
electromagnetic field inside the cavity can modulate the ground state
properties of weakly bound complexes. Controlling the field polarization, the
interactions can be stabilized or destabilized, and electron densities, dipole
moments, and polarizabilities can be altered. We demonstrate that
electron-photon correlation is fundamental to describe intermolecular
interactions in strong light-matter coupling. This work proposes optical
cavities as a novel tool to manipulate and control ground state properties,
solvent effects, and intermolecular interactions for molecules and materials.
