Virtual Orbital Many-Body Expansions: A Possible Route towards the Full Configuration Interaction Limit

Abstract

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