Visible-light-driven photocatalytic overall water splitting is deemed to be an ideal way to generate clean and renewable energy. The direct Z-scheme photocatalytic systems, which can realize the effective separation of photoinduced carriers and possess outstanding redox ability, have attracted a huge amount of interest. In this work, we have studied the photocatalytic performance of the bilayer MoSe₂/HfS₂ van der Waals (vdW) heterojunction following the direct Z-scheme mechanism by employing the hybrid density functional theory. Our calculated results show that the HfS₂ and MoSe₂ single layers in this heterojunction are used for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The charge transfer between the two layers brought about an internal electric field pointing from the MoSe₂ layer to the HfS₂ slab, which can accelerate the separation of the photoinduced electron–hole pairs and support the Z-scheme electron migration near the interface. Excitingly, the optical absorption intensity of the MoSe₂/HfS₂ heterojunction is enhanced in the visible and infrared region. As a result, these results reveal that the MoSe₂/HfS₂ heterojunction is a promising direct Z-scheme photocatalyst for photocatalytic overall water splitting.

With the continuous development of topological properties in condensed matter systems, the current research focus has been expanded into phononic bosonic states. Compared with the conventional electronic fermions, topological phonons exhibit very distinct features. In this study, based on density functional calculations, we have systematically investigated the topological phonons in the ternary phosphide compound BaLiP. Coincident nodal line and nodal surface states are revealed in the middle part of the phononic spectrum and they are formed by the same two phonon bands. Detailed band structure mechanism and symmetry operation formalism are provided. More importantly, evident surface states are observed from the entire nodal line and they are all well separated from the bulk state projection, very beneficial and preferable for future experimental investigation. Lastly, the mechanical properties are also examined and several important parameters are provided, which can be very useful for the practical application. Considering the multiple advantages of the topological nodal states in this material, the corresponding experimental study can be immediately inspired.