Researchers have developed a theoretical method to predict how vacuum fluctuations within an optical cavity can alter the structural properties of two-dimensional van der Waals (vdW) materials. This advancement, in the field of cavity quantum materials, aims to modify ground-state properties of matter without external driving. Previously, cavity-induced changes in vdW interactions had been predicted for molecular systems, but an efficient description for extended materials was lacking.

The team introduced a periodic formulation of the photon many-body dispersion (pMBD) functional within the framework of Quantum Electrodynamical Density-Functional Theory (QEDFT). This methodology allows modeling the interaction between materials and electromagnetic vacuum fluctuations. The method, combined with efficient **q**-point sampling, was applied to bilayer hexagonal boron nitride (hBN) and graphene.

The simulation results predict significant changes: a modification in layer stacking, an increase in equilibrium interlayer distances, and a softening of layer breathing modes as the light-matter coupling strength increases. These findings establish cavity vacuum fluctuations as a tuning knob for adjusting the structural properties of vdW materials, opening new avenues for engineering materials with tailored properties.