Supplement Number 1

See the supplementary material for the phonon spectra of monolayer MA2Z4 and M2A2Z4 (Figs. S1-S11); the ternary convex hulls of representative monolayer materials (Fig. S12); the Brillouin zone paths of monolayer 2H-MA2Z4, 1T-MA2Z4, and α-M2A2Z4 phases (Fig. S13); the band structures of the above-mentioned monolayer MA2Z4 and M2A2Z4 systems (Figs. S14-S22); and the average atomic masses of monolayer MA2Z4 and M2A2Z4 (Table S1).