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Promoting carrier separation and migration is the key factor to improve photocatalytic performance. In this work, we proposed a novel WSi 2 N 4 /MoSi 2 N 4 heterostructure including six different stacking configurations, in which the AB stacking configuration is thermodynamically most stable and can satisfy the requirement of overall water splitting. The presence of an internal electric field owing to the symmetry breaking will promote the carrier separation to different layers, and the low exciton (e−h pairs) binding energy (0.12 eV) and high carrier mobility further boost the separation and migration of electrons and holes; these results demonstrate that heterojunctions have high carrier activity and good photocatalytic performance. The high light absorption coefficient (∼10 5 cm −1 ) and enhanced visible light absorption also further support our theoretical predictions. Moreover, the research of nonadiabatic molecular dynamics provides a deeper understanding that the time of carrier transfer is much longer than e−h recombination (2420 fs for electrons, 67 ns for e−h recombination) and its intrinsic photocatalytic mechanism. These findings indicated that AB stacking with ultrafast carrier transport is an excellent photocatalyst.

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