In this section, the self-diffusion processes on the low-index surfaces are showcased as an example. It should be noted that only the hopping and exchange processes on the (100) facets were included in the respective force field training. All other reaction pathways served to validate the quality and reliability of the obtained force field parameter set. An overview of the respective pathways can be found in Fig. . The respective ReaxFF activation energies and their DFT-PBE target values are summarised in Table . ), (c) Li(110), and (d) Na(111) and Li(111). The most stable adsorption site of the respective facet was set as the initial state, i.e. hollow (h), longbridge (lb), ontop (ot) and fcc. Here, a filled circle highlights the starting position, and a framed circle indicates possible end positions of the diffusion pathways. Atoms participating in the exchange process are marked with an Ex. label. The calculated forward and reversed activation energies are given in Table . The obtained ReaxFF activation energies for the hopping processes (h 0 ↔h 1 , h 0 ↔h 2 ) on Na(100) and Li(100) are marginally elevated compared to the DFT-PBE values but within the range of the calculated standard deviations. It was further possible to sufficiently describe the exchange process h 0 ↔h 2 (Ex.) for Li, while for sodium, the process was overestimated by the exchange process fcc 0 ↔fcc 1 (Ex.) was identified as the dominant diffusion mechanism.