In any case, w ref is expected to decrease with the number of correlated electrons regardless of the type of molecular system considered. Importantly, in most applications the interest is in relative energies, e.g. when computing vertical transition energies or comparing different conformations. For a balanced and consistent account of the electron correlation effects in these situations, it is crucial that the reference weight is commensurate among all structures and states considered. This simple guideline provides a prescription on how to use w ref in practice. In calculations involving several electronic states, and in agreement with previous works, we consider as a rule of thumb deviations of more than 10 % from the state with largest w ref , typically the ground state, as potentially damaged by intruder states. At the same time, the reference weight of any electronic state should be a smooth function of the molecular geometry, insomuch as the electronic energy is. This is particularly important in the calculation of potential energy surfaces and curves, such as for molecular dynamics simulations and the dissociation of diatomics.