As well as inducing a metallic phase, increasing the fluorine content x increases the number of unpaired electrons per niobium, resulting in an increase in overall spin density (Fig. ). This leads to an increase in the energy difference between the Nb 3d majority and minority spin bands as the majority band occupation is increasingly stabilised, until a transition to a half-metallic phase occurs between x = 0.20 and x = 0.44. There is some uncertainty in this transition with several borderline half-metal/metal results, indicated by the overlapping shaded area in Fig. . This uncertainty reflects the proximity in energy of metallic and half-metallic states in this region, and the corresponding difficulties in achieving a robust self-consistent minimum energy. The splitting between the minority and majority Nb 3d spin states can be seen in Fig. showing the half-metallic state for x = 1.1. Furthermore, Fig. shows an increase in the minority spin band gap as x increases corresponding to this splitting. The dispersive nature of the conduction bands (Fig. ) indicate this half-metallic phase should have good conductivity, desirable for spintronics applications.