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escf and egrad can exploit point group
symmetry for all finite point groups (with up to 99-fold
→ $symmetry). The response and
eigenvalue problems (7.4) and (7.7)
decompose into separate problems for each IRREP that are solved
independently. For excited state and instability calculations, it is
thus necessary to specify the IRREPs to be treated ($soes,
see below). For response calculations, the perturbation is
automatically subduced into irreducible components. The overall
speedup compared to C1 symmetry is approximately 1/g, where g
denotes the point group order. For spin-restricted closed-shell
ground states, spin symmetry is used to further reduce the dimension
of the response and eigenvalue problems by a factor of 2.