The electronic structure of clean and Ga- or N-covered $1\times 1$ GaN(0001) and $\mathrm{GaN}\left(0001\mathrm{}¯\right)$ surfaces is studied using the local-density approximation of density-functional theory employing ab initio pseudopotentials together with Gaussian orbital basis sets. We use both standard and self-interaction- and relaxation-corrected pseudopotentials. The latter allow for a most accurate description of the electronic structure of these surfaces. Comparing the formation energies for the clean and adatom-covered $1\times 1$ configurations, we determine optimal surface structures for various growth conditions. For the GaN(0001) surface in the Ga-rich case, we find a structural model consisting of Ga adatoms adsorbed in $T_4$ positions above the substrate surface to be most favorable. In the N-rich case, the clean GaN(0001) surface is the most stable $1\times 1$ configuration. For the $\mathrm{GaN}\left(0001\mathrm{}¯\right)$ surface, our results for both Ga- and N-rich growth conditions indicate that a full monolayer of Ga adatoms adsorbed in on top positions is the most stable configuration. Our theoretical results allow for a comparison of full calculations of the surface electronic structure for a number of optimized structural models with most recent angle-resolved photoemission spectroscopy data.

• Received 5 December 2000

DOI:https://doi.org/10.1103/PhysRevB.64.035305