▎ 摘　　要

We study the gate-voltage induced gap that occurs in graphene bilayers using ab initio density functional theory. Our calculations confirm the qualitative picture suggested by phenomenological tight-binding and continuum models. We discuss enhanced screening of the external interlayer potential at small gate voltages, which is more pronounced in the ab initio calculations, and quantify the role of crystalline inhomogeneity using a tight-binding model self-consistent Hartree calculation.