Empirical bond polarizability model for fullerenes

The static polarizability properties and the Raman-scattering intensities in molecular ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ are found to be well reproduced by a bond polarizability model with parameters similar to those obtained from studies of hydrocarbons. For the Raman spectrum of ${\mathrm{C}}_{60}$ with off-resonance infrared laser excitation, a fit using first-principles vibrational eigenvectors yields ${\mathrm{\alpha }}_{\mathrm{\parallel }}^{\prime }$-${\mathrm{\alpha }}_{\mathrm{\perp }}^{\prime }$=2.30 A${\mathrm{̊}}^2$, 2${\mathrm{\alpha }}_{\mathrm{\perp }}^{\prime }$+${\mathrm{\alpha }}_{\mathrm{\parallel }}^{\prime }$=2.30 A${\mathrm{̊}}^2$, ${\mathrm{\alpha }}_{\mathrm{\parallel }}$-${\mathrm{\alpha }}_{\mathrm{\perp }}$=1.28 A${\mathrm{̊}}^3$ for single bonds and ${\mathrm{\alpha }}_{\mathrm{\parallel }}^{\prime }$-${\mathrm{\alpha }}_{\mathrm{\perp }}^{\prime }$=2.60 A${\mathrm{̊}}^2$, 2${\mathrm{\alpha }}_{\mathrm{\perp }}^{\prime }$+${\mathrm{\alpha }}_{\mathrm{\parallel }}^{\prime }$=7.55 A${\mathrm{̊}}^2$, ${\mathrm{\alpha }}_{\mathrm{\parallel }}$-${\mathrm{\alpha }}_{\mathrm{\perp }}$=0.32 A${\mathrm{̊}}^3$ for double bonds, with (${\mathrm{\alpha }}_{\mathrm{\parallel }}$-${\mathrm{\alpha }}_{\mathrm{\perp }}$) for the single bond arbitrarily set equal to its value in ethane, namely, 1.28 A${\mathrm{̊}}^3$. The transferability of these parameters to ${\mathrm{C}}_{70}$ is discussed in detail. © 1996 The American Physical Society.