  We study the photoionization properties of the C_60 versus C_240 molecule in
a spherical jellium frame of density functional method. Two different
approximations to the exchange-correlation (xc) functional are used: (i) The
Gunnerson-Lundqvist parametrization [Phys. Rev. B 13, 4274 (1976)] with an
explicit correction for the electron self-interaction (SIC) and (ii) a
gradient-dependent augmentation of (i) by using the van Leeuwen and Baerends
model potential [Phys. Rev. A 49, 2421 (1994)], in lieu of SIC, to implicitly
restore electrons' asymptotic properties. Ground state results from the two
schemes for both molecules show differences in the shapes of mean-field
potentials and bound-level properties. The choice of a xc scheme also
significantly alters the dipole single-photoionization cross sections obtained
by an abinitio method that incorporates linear-response dynamical correlations.
Differences in the structures and ionization responses between C_60 and C_240
uncover the effect of molecular size on the underlying physics. Analysis
indicates that the collective plasmon resonances with the gradient-based
xc-option produce results noticeably closer to the experimental data available
for C_60.
