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Abstract

We show that electrodynamic dipolar interactions, responsible for long-range fluctuations in matter, play a
significant role in the stability of molecular crystals. Density functional theory calculations with van der Waals
interactions determined from a semilocal “atom-in-a-molecule” model result in a large overestimation of the
dielectric constants and sublimation enthalpies for polyacene crystals from naphthalene to pentacene, whereas
an accurate treatment of nonlocal electrodynamic response leads to an agreement with the measured values for
both quantities. Our findings suggest that collective response effects play a substantial role not only for optical
excitations, but also for cohesive properties of noncovalently bound molecular crystals.