First-principles calculation of the structure and elastic properties of a 3D-polymerized fullerite

In this paper we present results obtained from first-principles calculations concerning the crystal structure and elastic properties of a three-dimensional-polymerized fullerite. The orthorhombic structure we studied was first proposed on the basis of an x-ray-diffraction analysis of samples quenched from high-pressure and high-temperature conditions. The single-crystal bulk modulus for the optimized structure is 302 GPa, and Hill’s average shear modulus for the polycrystalline aggregate is 301 GPa. Our results indicate that this orthorhombic fullerite should be hard, but not harder than diamond ~a Knoop hardness of about 30 GPa!, with a fracture toughness probably higher than that for diamond.