The reflectance difference spectra of nine GaAs(001) surface reconstructions, (2 x 4)β2, (2 x 4)α, (2 x 4)γ2, (2 x 4)β1, (2 x 4)γ1 and c(4 x 4) reconstructions on As-rich surface and (4 x 2)β2, (4 x 2)α and (4 x 2)β1 reconstructions on Ga-rich surface, were studied by using the nearest-neighbour sp3s* tight-binding method. The surface atomic positions and the tight-binding interaction parameters were obtained by the ab initio pseudopotential calculations. It was found that the reflectance difference spectra have considerably different features between As- and Ga-rich surface reconstructions. The reflectance difference spectra of As-rich surfaces were mainly understood by transitions between top As-dimer states, while the reflectance difference spectra of Ga-rich surfaces were explained by the surface electronic states resulting from the sinkage of surface Ga atoms into bulk layers. Reflectance Difference Spectra Calculations of GaAs(001) As- and Ga-rich Reconstruction Surface Structures. M.Murayama, K.Shiraishi, T.Nakayama: Japanese Journal of Applied Physics, 1998, 37, 4109-14