In Fig. , we see that the two states that only appear in the presence of the PD, namely the embedded and buried states, are more energetically stable than the states that also arise in the absence of the PD (the adsorbed and standing states). More importantly, these new states mainly fall to the left of the line showing the most stable N 2 -lithium interaction in the absence of the PD and also the most stable energy for forming surface nitrides (See Fig. ).