Fig. shows the diffusion barrier ∆E diff and the difference between the transition and diffusion barriers ∆E tran -∆E diff as a function of ρ. ∆E diff shows similar trends as ∆E tran , which decreases as ρ increases. This difference in energy barriers may be closely related to the solidification mechanism of non-metallic systems. Unlike metallic systems, non-metallic systems tend to form flat solid/liquid interfaces during solidification, effectively reducing the number of dangling bonds .