Calculations using CASPT2D served to carry out an unbiased analysis of the various techniques, however, in practice the full CASPT2 approach is the method of choice. Hence, we repeated all the calculations with the latter, investigating to what extent the off-diagonal couplings in the zeroth-order Hamiltonian affect the results obtained with CASPT2D. In Table we show the RMSD and MAD obtained in the NOISP analysis with the CASPT2 method. The real shift is still plagued by accidental intruder states due to denominators that are close to the negative level shift parameter, and only for ε = 0.3 E h there are no such cases.