Coordinate systems for H2 on Pt(211). (a) Top view of the (1×1) unit cell showing also the dissociated reference geometry of H2 used to converge the computational setup with respect to the adsorption en- ergy Eads. First and second layer Pt atoms are in silver and dark gray, respectively. H atoms are blue colored. (b) Side view of the slab model. The Z-axis (molecule-surface distance) in the standard coordinate system drawn in black is aligned with the normal to the macroscopic surface. X and Y are the lateral components of the COM position of H2 indicated by a red dot. Furthermore, r is the interatomic H−H distance (not shown) and the angular orientation is specified by the polar angle θ ∈ [0,π] and the azimuthal angle φ ∈ [0, 2π] (not shown). The angular orientation of H2 in the internal coordinate system is defined with respect to the normal of the (111) terrace, as shown in red. The two coordinate systems include an angle χ of 20◦. The corresponding angular coordinates are {θ′,φ′}. The surface lattice constants are LX = 6.955 Å and LY = 2.839 Å.