STIFFNESS OF A SOLID COMPOSED OF C60 CLUSTERS

We calculate the equilibrium structure of fullerite, a solid composed of C60 clusters, as a function of external pressure. We find that at zero pressure, carbon atoms in neighboring "fullerene" clusters are no closer than 2.65 angstrom apart and interact by pairwise van der Waals forces. At increasing pressures, we observe a gradual transition to a hard-core repulsion between neighboring clusters. Only at high pressures, beyond almost-equal-to 70 GPa, does the bulk modulus of fullerite exceed that of diamond.