energy is $-6.999$ MeV. It can be seen that the non-relativistic expansion with the reconstituted FW transformation achieves a fast convergence. Shown in a smaller scale in Panel (b) of Fig. \[fig1\], the differences between the single-particle energies obtained at the $1/{M^\ast}^3$ order and the exact ones are less than $0.1$ MeV for the deeply bound states, and become slightly larger to around $0.2$ MeV for the weakly bound states. The three orbitals that show the biggest negative differences are the $1g_{9/2}$ state at $-28.072$ MeV, $1h_{11/2}$ state at $-18.784$ MeV, and $1i_{13/2}$ state at $-9.267$ MeV. Their deviations from the corresponding exact values are $-152$, $-239$, and $-325$ keV, respectively. In contrast, the orbital that shows the biggest positive difference is the $1h_{9/2}$ state at $-14.027$ MeV, whose deviation from the corresponding exact value is $89$ keV.

In order to understand these energy differences for the states with large angular momenta $l$, we recall that, although a discrepancy between the results of the conventional SRG method [@Guo2019Phys.Rev.C99.054324] and FW transformation [@Guo2019Chin.Phys.C43.114105] appears starting from the $1/M^3$ order, their spectrum of the single-particle energies are identical to each other [@Guo2019Chin.Phys.C43.114105]. Thus the detailed $1/M^4$-order results of the conventional SRG method 