The fact that Strategy D [see Fig. (b)] tends to increase the energy of CrO is worth commenting on. This behaviour reflects cross-contamination between two numerical issues used in D: 1) the use of an approximate Hessian in Newton iteration for the orbital optimization scheme; 2) non-smoothness of the DM21 DFA as a functional of orbitals. Issue 1 [see Eq. (A1) in Appendix A below] can lead the orbital optimization algorithm to sometimes "climb up hills" when the approximate Hessian sometimes has the wrong 'sign'. In well-behaved systems, or with well-behaved DFAs, the ascent is followed by a descent once the 'sign' gets fixed -indeed, ascent sometimes helps the algorithm iterate to the global minima. But Issue 2 (evidenced by very large fluctuations in the energy) makes both the Hessian and its approximation de facto discontinuous. Discontinuities can trap the algorithm in regions of orbital space where the energy varies rapidly. Continued iteration may eventually find the minima, although the fluctuations of around 1 Ha (i.e. ∼ 100× MAE in atomization energies of converged cases) in CrO certainly make this challenging.