Structure and stability of β-Mo2C bulk and surfaces: A density functional theory study

Density functional theory calculations have been performed on the structure and stability of β-Mo2C bulk and the corresponding low-index surfaces. The eclipse configuration with a Mo-C-Mo-C stacking is the most stable, followed by the structure with a Mo-C-Mo-Mo-C stacking where there is an empty carbon layer every fourth layer. For (0 0 1) and (1 0 0) surfaces, the pure C terminations are more stable than the pure Mo terminations. For (0 1 0) and (1 1 1) surfaces, the Mo terminations are more stable than the C terminations. For the (0 1 1) surface, the mixed Mo/C termination is a little more stable than the Mo termination. Relaxation of these surfaces is moderate with no relaxation degree exceeding 12.8%. Among these surfaces, the mixed Mo/C termination of the (0 1 1) surface is the most stable with the lowest surface free energy, followed by the (1 0 1) surface and the TMo-2 termination of the (0 1 0) surface.