The presence of more than one significant λ i in the SVD of x + y can be driven by symmetry-induced orbital degeneracies. Such is the case for benzene, whose frontier MOs (Fig. ) consist of a pair of degenerate e 1g orbitals (HOMO and HOMO -1) along with a pair of degenerate e 2u orbitals (LUMO and LUMO + 1). In small basis sets, there is essentially no difference between the canonical MOs and the NTOs for the lowlying excited states and they can be used interchangeably in the following discussion. Four singly-excited determinants can be constructed from the four aforementioned orbitals, and together these make up the first four singlet excited states of benzene. These states are: