  An approximation for the exchange-correlation energy of
reduced-density-matrix-functional theory was recently derived from a study of
the homogeneous electron gas (N.N. Lathiotakis, N. Helbig, E.K.U. Gross, Phys.
Rev. B 75, 195120 (2007)). In the present work, we show how this approximation
can be extended appropriately to finite systems, where the Wigner Seitz radius
r_s, the parameter characterizing the constant density of the electron gas,
needs to be replaced. We apply the functional to a variety of molecules at
their equilibrium geometry, and also discuss its performance at the
dissociation limit. We demonstrate that, although originally derived from the
uniform gas, the approximation performs remarkably well for finite systems.
