Nonlinear optical susceptibilities of fullerenes in the condensed phase

We present results for nonlinear optical susceptibilities of fullerenes, including ${\mathrm{C}}_{60},$ ${\mathrm{C}}_{70},$ and ${\mathrm{C}}_{84},$ in the condensed phase from large-scale ab initio calculations using self-consistent reaction field theory and an analytical local-field method. It is shown that the intermolecular polarization interaction has significant effects on the nonlinear properties of the fullerenes, and that, in some contrast to other organic species, nondipolar contributions to this interaction are important. Based on the theoretical and experimental results for the polarizability of ${\mathrm{C}}_{60}$ in the gas phase, a general local-field factor for ${\mathrm{C}}_{60}$ film has been obtained, which is found to be quite different from the classical Lorenz-Lorentz local-field factor. The calculated and experimental nonlinear optical susceptibilities of ${\mathrm{C}}_{60}$ are in good agreement provided the comparison is made on the same basis, viz at nonresonant frequencies and considering the relevant macroscopic quantities. The dielectric and density dependence of the nonlinear optical susceptibilities of ${\mathrm{C}}_{70}$ are discussed.