We studied the structures and energies associated with 8 types of point defects on the [0001] surface of hexagonal gallium nitride (GaN) by modeling: (1) Ga vacancies (VGa), (2) N vacancies (VN), (3) substitution of N by Ga (GaN), (4)substitution of Ga by N (NGa), (5) Ga octahedral interstitial defects (Gao), (6) Ga tetrahedral interstitial defects (GaT), (7) N octahedral interstitial defects (No), and (8) N tetrahedral interstitial defects (Nr).Using a plane-wave ultrasoft pseudopotential method, we calculate these defect structures, simulate the shift, bonding, and relaxation reconstruction of surface atoms in response to the formation of these defects and also calculate the formation energies of these defects.We find that the Ga-related defects only slightly affect the surface, whereas all N-related defects induce substantial surface reconstruction.In particular, the formation of NT not only induces distortion of the surface structure, but also significantly influences the structure of the deeper lattice space.Calculations of formation energies suggest that, in Ga-rich conditions, Gao forms most easily, followed by GaN, VN, and GaT.In comparison, in N-rich conditions, VGa forms most easily.In all environments, Gao, GaN, and VGa form more easily than VN, and the formation of octahedral interstitial defects requires less energy than tetrahedral interstitial defects, which suggests it is difficult to form tetrahedral interstitial defects in the GaN (0001) surface.