  The inhomogeneous Singwi, Tosi, Land and Sjolander (ISTLS) correlation energy
functional of Dobson, Wang and Gould [PRB {\bf 66} 081108(R) (2008)] has proved
to be excellent at predicting correlation energies in semi-homogeneous systems,
showing promise as a robust `next step' fifth-rung functional by using dynamic
correlation to go beyond the limitations of the direct random-phase
approximation (dRPA), but with similar numerical scaling with system size. In
this work we test the functional on fourteen spherically symmetric, neutral and
charged atomic systems and find it gives excellent results (within 2mHa/$e^-$
except Be) for the absolute correlation energies of the neutral atoms tested,
and good results for the ions (within 4mHa/$e^-$). In all cases it performs
better than the dRPA. When combined with the previous successes, these new
results point to the ISTLS functional being a prime contender for
high-accuracy, benchmark DFT correlation energy calculations.
