Contribution of nuclear displacements to the static polarizability of molecules in an external electric field: Application to fluorinated fullerenes ${\mathrm{C}}_{60}{\mathrm{F}}_n$

In molecules with ionic contributions to the binding, the contribution of nuclear displacements (due to the external field) to the static polarizability can be decisive. Using the finite field method, we optimized the structure with and without a finite external electric field by a total energy minimization and we calculated the polarizability from the induced dipole moment. In ${\mathrm{C}}_{60}{\mathrm{F}}_n$, fluorination mostly increases the polarizability. Only for $n=2$ and 18, where the molecule without an external field has a very large dipole moment, does fluorination decrease it. For large $n$ ($n=20$, 36, and 48), the polarizability per added F atom due to nuclear displacements is increased by a factor of about 2. The validity of the additivity model has been discussed.

Figure 1

Structure of ${\mathrm{C}}_{60}{\mathrm{F}}_n$ for a zero external field. (The $x$, $y$, and $z$ axis are the abscissa, the ordinate, and the axis pointing out of the figure, respectively.)