Hybrid DFT results for Kr 2 are presented in Fig. ). The B3LYP functional affords an unbound potential curve, whereas results obtained using either M06-2X or ωB97M-V 26 are reasonably accurate. Both of these functionals are meta-GGAs, according to the classification scheme known as Jacob's Ladder, and are examples of methods designed to capture dispersion from first principles. Both functionals work rather well for this example, despite its extremely small interaction energy.