  The projected oscillator orbitals (pOOs) are localized virtual orbitals
constructed by multiplying localized occupied orbitals by harmonics. Following
a recent paper by Mussard and \'Angy\'an (Theor Chem Acc 134:1, 2015), further
developments of projected oscillator orbitals are shown, notably the equations
for pOOs of general order as well as their overlaps are derived. The
performance of these localized virtual orbitals is demonstrated up to third
order. It is found that a good fraction of the aug-cc-pVQZ RPA correlation
energy is recovered by use of a smaller number of pOOs. This is especially true
where considering only the long-range correlation energy, which is important
for the description of London dispersion forces.
