  In the present letter, it is demonstrated how full configuration interaction
(FCI) results in extended basis sets may be obtained to within sub-kJ/mol
accuracy by decomposing the energy in terms of many-body expansions in the
virtual orbitals of the molecular system at hand. This extension of the FCI
application range lends itself to two unique features of the current approach,
namely that the total energy calculation can be performed entirely within
considerably reduced orbital subspaces and may be so by means of embarrassingly
parallel programming. Facilitated by a rigorous and methodical screening
protocol and further aided by expansion points different from the Hartree-Fock
solution, all-electron numerical results are reported for H$_2$O in polarized
core-valence basis sets ranging from double-$\zeta$ (10 $e$, 28 $o$) to
quadruple-$\zeta$ (10 $e$, 144 $o$) quality.
