Total energy and electronic structure calculations based on density functional theory are performed in order to determine the atomic structure and electronic properties of clean and hydrogen‐adsorbed Al₀.₅In₀.₅P(001) surfaces. It is found that most of the stable surfaces obey the electron‐counting rule and are characterized by surface atom dimerization. The dimer‐related surface states are predicted to occur in the vicinity of the bulk band edges. For a very narrow range of preparation conditions, ab initio thermodynamics predicts metal atomic wires formed by surface cations. A surface covered with a monolayer of buckled phosphorus dimers, where half of the phosphorus atoms are hydrogen saturated, is found to be stable for metal–organic vapor‐phase epitaxy growth conditions. The occurrence of this structure is confirmed by low‐energy electron diffraction and X‐ray photoelectron spectroscopy data measured on epitaxially grown Al₀.₅₂In₀.₄₈P(001) epilayers lattice matched to GaAs.
