Electron-electron correlations in fullerene C-60 probed by incoherent scattering of x rays

The static structure factor of electrons in fullerene has been obtained by a properly designed x-ray diffraction experiment. Due to the intense diffuse scattering caused by the orientational disorder of the C-60 molecules in fullerene, the experiment presented several difficulties. Nonetheless, the data were accurate enough to provide an estimate of the exchange-correlation energy and to make a valuable comparison of the static structure factors of fullerene and diamond. The observed value of the exchange-correlation energy, which is larger in fullerene than in diamond, suggests a clear link between carbon polymorphism and dynamic electron correlations. The experimental data of static structure factor of fullerene, together with the derived exchange-correlation contribution to the cohesion and the pair-correlation function, offer an interesting test on the validity of the local-density treatment of the electron correlations in solids.