First-principles studies of the atomic reconstructions of CdSe (001) and (111) surfaces

We have performed the first-principles total-energy calculations to investigate (2 x 1), (1 x 2), (2 x 2), (4 x 2) and (2 x 4) reconstructions of Cd- and Se-terminated CdSe(001) and (111) surfaces as a function of the surface stoichiometry and the Cd chemical potential. We find that there exist Cd dimers on the (001) surface and Se tetramers on the (111) surface. Comparing surface formation energies as a function of the Cd chemical potential mu(Cd), we find the Cd- vacancy and Se-vacancy (2 x 2) structures to be energetically favorable for the Cd- terminated (001) surface at high mu(Cd) and Se-terminated (001) surface at low mu(Cd), respectively. In contrast, an Se-tetramer (2 x 4) structure is more favorable than the vacancy structure for the Se-terminated CdSe(111) surface almost in the whole region of allowed mu(Cd).