Each metal site binds to two bridging NH2 on alternate sides forming parallel rows along the surface. While the NH2 groups are positioned at equal distance from the two metal sites the bond distances between the metal site and the nitrogen atom in the NH2 groups increases as the metal atom goes down in the group (2.14 Å for AlN, 2.20 Å for GaN and 2.39 Å for InN). The NH2 groups are shifted slightly from the line between the metal sites towards the hollow site, which could be due to repulsion from the nitrogen atom in the topmost surface layer. The angel of the bonds between the nitrogen of the NH2 group and the surface sites to the (0001) direction are 43° for both AlN and GaN and 41° for InN, showing that the groups are drawn close to the surface. The closeness to the surface together with the lack of any free electron pair on the nitrogen would make it hard for a metal precursor to find an adsorption site, without the surface reconstructing further.