@article {5, title = {Ab-initio theory of polar semiconductor surfaces: I. Methodology and the (2 x 2)reconstructions of GaAs(111)}, journal = {Phys. Rev. B}, volume = {35}, year = {1987}, pages = {9625}, author = {E. Kaxiras and Y. Bar-Yam and J.D. Joannopoulos and K.C. Pandey} }