where E LixNay is the total binding energy of the Li x Na y alloy phase, and E bulk Li , E bulk Na are the cohesive energy of the Li and Na bcc bulk phase, respectively. Table summarises the calculated structural and physical constants. Table : Calculated structural and physical constants for various bulk Li-Na alloy phases obtained from ReaxFF and DFT-PBE. The determined standard deviations obtained from BEEF-vdW 90 calculations are given in brackets. Lattice constants a 0 , b 0 , c 0 are given in Å, lattice angles α 0 , β 0 , γ 0 are given in °, energies of formation ∆ f E are given in eV, and bulk moduli B 0 are given in GPa. The energy of formation is reported per formula unit and is referenced to the bcc bulk phases of lithium and sodium (see Table ). Diffusion properties -For further evaluation of the Li-Na parameter set, the diffusion of a single Na adatom on perfect and imperfect Li(100) surfaces was investigated. This allows us to validate the description of both thermodynamically and kinetically controlled processes via the energy difference in the initial and final states and the computed activation energies, respectively. A schematic representation of the explored diffusion pathways is given in Fig. . The respective reversed and forward activation energies obtained from ReaxFF and DFT-PBE are listed in Table .