The valence-charge density of graphite

A full sphere of data extending to (sin θ/λ) = 1.2 Å^-1 and containing 1595 reflections was measured with small, natural, single crystals of graphite and Mo Kα radiation. With the structure assumed to be in space group P6₃/mmc, the valence-charge density of the two independent C atoms was represented by a finite multipole expansion containing products of single-exponential radial functions and tesseral harmonics. A full-matrix, least-squares refinement of the model charge was computed where populations of the multipole deformations, thermal parameters, scale, and extinction parameters were refined. The experimental data fit a model charge density containing highly directional build-ups of charge to 2 e Å^-3 between nearest neighbors in the basal plane. No structure was evident in the charge density between the basal planes. The refinable parameter, α, in the exponential radial function was 3.16 ± 0.05 bohr^-1. The charge density and associated parameters are consistent with strong covalent bonding of sp² character in the basal plane of graphite and minimal interactions between the layers.