Abstract
The low-frequency magneto-absorption spectra of monolayer and bilayer graphene are evaluated within the gradient approximation. On the basis of Peierls tight-binding model, we can draw the wave function distribution over its sublattices and bring them into the calculation of optical spectra. The optical selection rules and the absorption rate can be accurately determined. The interlayer interactions in bilayers effectively alter the Landau level structures and thus the absorption spectra, such as the field dependence of absorption lines and the appearance of double-peaked absorptions.