Density functional study of narrow cubic MnSe nanowires: Role of MnSe chains

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First-principles pseudopotential calculations are employed to study the structural stability, electronic, and magnetic properties of bulk, free chain, free (100) and (110) surfaces, and narrow [001] nanowires of MnSe in the rock-salt structure. The bulk computations reveal underestimation of the Mn 3d spin exchange splitting within generalized gradient approximation (GGA) and hence necessity of the GGA $+$ U scheme for improvement of this parameter toward experimental data. The obtained cohesive energies indicate higher stability of narrow MnSe nanowires with (100) facets and sharp square cross sections. A phenomenological model was applied to measure the energy costs for the creation of the facet and edge MnSe chains in MnSe nanowires. Comparing the electronic band structures and cohesive energies of the pristine and hydrogen-passivated MnSe[001] nanowires justifies efficient surface rehybridizations and, consequently, the absence of surface dangling bonds in various MnSe nanostructures.