where E slab is the total energy of the slab, E bulk is the bulk energy per atom, A is the surface area, and N is the number of atoms per supercell 100 . The calculated energy values of the low-index surfaces for sodium and lithium are given in Table . within the standard deviation of the DFT data, the surface energies for sodium are slightly downshifted by approximately 0.06 J m -2 . Nevertheless, the obtained data for both metal systems are internally consistent. Evidently, the developed force field can be applied to a wide range of metallic sodium and lithium surfaces. For both metals, the stabilities of the stepped surface structures are well reproduced and emphasise the transferability of the parameter set.