Figure 2: (a) Histogram of the relative formation energies and associated barrier energies (red squares and left vertical axis) of the ART nouveau-generated configurations for tetrainterstitials in iron modeled by the Ackland-Mendelev potential. The zero energy is the energy of the most stable configuration. The vertical axis on the right-hand side (associated with the bars) corresponds to the number of distinct minima found by ART nouveau. (b) Transition pathway for the unfaulting mechanism of the ring configuration of the tetrainterstitial, 𝐼 r i n g 4 , into the most stable configuration, 𝐼 4 𝜁 𝜍 0 (reproduced from [53]).