(color online) Calculated multilayer relaxation Δd_{n,n + 1} = 100(d_{n,n + 1} − d₀)/d₀ of Ni (002) surface by using EDM. The relative surface atomic structure is given in Fig. 1. DFT calculational models for QM and TR regions are both surface slab consisting of 25 (002) atomic layers repeated periodically along the z direction, separated by 12 Å vacuum layers. Periodic boundary condition is implemented in x and y directions.