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Band structures of Mn2AlSe4 monolay with different on-site Hubbard Ueff values；Phonon spectra and AIMD simulation of Mn2GaSe4 and Mn2InSe4 monolayers; Young's modulus and Poisson's ratio, elastic constants, considered magnetic configurations, projected density of states, Angular dependence of MAE, specific heat as a function of temperature and band structures considering SOC effect of Mn2XSe4 monolayers; Wannier charge center (WCC) and anomalous Hall conductivity (AHC) of Mn2GaSe4 and Mn2InSe4 monolayers; Band structures of Mn2XSe4 monolayer without and with considering SOC effect.