Structure and energetics of LaAlO 3 (001) surfaces

Reconstructions of the LaAlO3 (001) surface are studied using hybrid density functional calculations. We calculate surface energies as a function of O and Al chemical potentials for both the LaO-and AlO2-terminated surfaces. We find that the (3 x 2) Al adatom is the most stable reconstruction on the AlO2 termination, with the (2 x 2) O vacancy slightly higher in energy. On the LaO termination, the (3 x 2) La vacancy is the most stable reconstruction. Overall, the LaO termination with the (3 x 2) La vacancy has the lowest surface energy, in the absence of impurities. However, our calculations also indicate that the presence of hydrogen alters the stability of the LaO versus the AlO2 termination. Under Al-rich conditions, H binds to an O atom forming a (2 x 1) H-adatom reconstruction on the AlO2-terminated surface, whereas under La-rich conditions a (2 x 1) OH adsorbate reconstruction forms on the LaO-terminated surface. These reconstructions are found to be the most stable terminations over a wide range of H and O chemical potentials.