Plasmon resonances in fullerene ions
A.K. Petrov*, V.K. Ivanov+, A.V. Solov'yov#, and W. Greiner*
*Herzen University, Moika 48, 191186 St Petersburg, Russia
+St Petersburg State Polytechnic University, Politechnicheskaya 29, 195251 St.Petersburg, Russia
#Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe University, Robert-Mayer Str. 10, D-60054 Frankfurt am Main, Germany
The photoionization cross sections of the fullerene C60 and its positive ions C60q+ (q=1,2,3) are calculated within the photon energy range from the ionization thresholds up to 80 eV and compared with the recent experimental data [1] and other calculations for C60+. The main attention is paid the giant plasmon resonance in photoabsorption.
The calculations are performed within the Local Density Approximation. The basic Kohn-Sham equations are used for determining of the single-electronic wave functions. The calculations are performed within the jellium model for positive core for both the sphere and the spherical layer: valence electrons are considered in the averaged field of 60 ions of C+4 [2]. In the present work the theoretical approach is improved by means of using the Perdew-Wang parametrization for the exchange-correllation energy functional. 
The phototransition amplitude of each orbital is calculated both within the single-electron approximation and also by taking into account many-electron correlations within the Random Phase Approximation. The total photoionization cross section is calculated as a sum of partial cross sections for each orbital. 
The calculated photoionization cross sections for the neutral fullerene, as well as for its ions indicate the giant plasmon resonances with positions of ~20 eV for all fullerenes. The physical nature of the resonances is discussed. This is in a good agreement with the classical Mie theory and the experimental data [1] for the ions C60+, C602+ and C603+. The analysis shows that the dominant contribution in the giant resonance for the total cross sections is due to the ionization from the 6g and the 5f shells with some contribution from the 4d and 2s shells. The photoionization cross sections calculated in the present work fulfill the sum rule for all fullerenes under the consideration, so in contrast to the previous calculations [2] they are not scaled by any factor.
This work is supported by INTAS (grant N 09-15-71nn).

[1]	S.W.J. Scully et al. Phys. Rev. Lett. 94, 065503 (2005).
[2]	R.G. Polozkov, V.K. Ivanov, A.V. Solov'yov, J. Phys. B 38, 4341 (2005).