Structural and electronic properties of transition-metal chalcogenides Mo₅S₄ nanowires

Transition-metal chalcogenide nanowires (TMCN) as a viable candidate for nanoscale applications have been attracting much attention for the last few decades. Starting from the rigid building block of M₆ octahedra (M=transition metal), depending on the way of connection between M₆ and decoration by chalcogenide atoms, multiple types of extended TMCN nanowires can be constructed based on some basic rules of backbone construction proposed here. Note that the well-known Chevrel-phase based M₆X₆ and M₆X₉ (X=chalcogenide atom) nanowires, which are among our proposed structures, have been successfully synthesized by experiment and well studied. More interestingly, based on the construction principles, we predict three new structural phases (the cap, edge, and C&E phases) of Mo₅S₄, one of which (the edge phase) has been obtained by top-down electron beam lithography on two-dimensional MoS₂, and the C&E phase is yet to be synthesized but appears more stable than the edge phase. The stability of the new phases of Mo₅S₄ is further substantiated by crystal orbital overlapping population (COOP), phonon dispersion relation, and thermodynamic calculation. The barrier of the structural transition between different phases of Mo₅S₄ shows that it is very likely to realize an conversion from the experimentally achieved structure to the most stable C&E phase. The calculated electronic structure shows an interesting band nesting between valence and conduction bands of the C&E Mo₅S₄ phase, suggesting that such a nanowire structure can be well suitable for optoelectronic sensor applications.