24Mg: 4p + 4n in sd shell; TBME scale = (18/24)^0.3 = 0.917315
m-scheme basis dimension (Jz=0): 28503
lowest eigenvalues (MeV):
      -87.1044
      -85.6021
      -82.9883
      -82.7320
      -82.0341
      -81.2219
      -79.7662
      -79.6227
      -79.3076
      -79.2863

=== validation vs two independent references (both run on this machine) ===
state    this code     cosmo (Xlevels)   BIGSTICK v7.11.4
0+(1)    -87.1044      -87.1044          -87.10445
2+(1)    -85.6021      -85.6021          Ex 1.502 -> -85.602
2+(2)    -82.9883      -82.9883          Ex 4.116 -> -82.988
4+(1)    -82.7320      -82.7320          Ex 4.372 -> -82.732
3+(1)    -82.0341      -82.0302          (cosmo doc prints -82.0294 for the
4+(2)    -81.2219      -81.2219           same level: their Davidson tolerance
0+(2)    -79.7662      -79.7662           is ~5 meV on this state; eigsh here
2+(3)    -79.6227      -79.6227           runs to machine precision)
5+(1)    -79.3076      -79.3076
1+(1)    -79.2863      -79.2863
basis dimension (Jz=0): 28503  (= BIGSTICK)   runtime ~8.5 s single-core
TBME scaling (18/24)^0.3 = 0.917315 (= BIGSTICK's "1.0 18.0 24.0 0.3" line)

18O check (scale 1): all ten levels match cosmo to every printed digit,
ground state -11.9318 MeV.