To ascertain the involvement of the inner p-orbitals in the metal-metal bonds, it is crucial to check the dependency from the interatomic distances. To be quantitative, we have fully relaxed the B1 and B2 phases of RbF from 0 to 10 GPa, and monitored the ICOHP values for the various interactions (Figure ). This analysis shows that the -ICOHP for Rb-Rb in B1 at 10 GPa, equal to 0.6 eV/bond, is less than half than the interaction strength calculated for the B2 phase at 0 GPa (1.3 eV/bond), despite differing by only 0.2 Å in length. Moreover, the metalmetal -ICOHP trends in function of bond lengths have different slopes for the two phases, showing that the Rb-Rb contacts in B1 and B2 are intrinsically different. Therefore, the strength of the metal-metal interactions is not just a matter of intermetallic distance.