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Point group symmetry.

escf and egrad can exploit point group symmetry for all finite point groups (with up to 99-fold symmetry axes, $ \rightarrow$ $symmetry). The response and eigenvalue problems (7.4) and (7.7) decompose into separate problems for each IRREP that are solved independently. For excited state and instability calculations, it is thus necessary to specify the IRREPs to be treated ($soes, see below). For response calculations, the perturbation is automatically subduced into irreducible components. The overall speedup compared to $ C_1$ 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.

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