Surface structures An asymmetric slab A symmetric slab-to to create size- cancel the artificial Repetition of sl dependent dipole electrostatic field to relax the top three Vacuum layers and keep the bottom two layers Vacuum d12 fixed at bulk positions. Relaxed layers d23 Fixed layers d2 brlk-lika Five-layer slab d23 d23 Relaxed layers Top 3 layers relaxed VacuumSurface structures to relax the top three layers and keep the bottom two layers fixed at bulk positions. An asymmetric slab – to create size￾dependent dipole A symmetric slab – to cancel the artificial electrostatic field