We use density functional theory and the van der Waals density functional
(vdW-DF) method to determine the binding separation in bilayer and bulk
graphane and study the changes in electronic band structure that arise with the
multilayer formation. The calculated binding separation (distance between
center-of-mass planes) and binding energy are 4.5-5.0 {\AA} (4.5-4.8 {\AA}) and
75-102 meV/cell (93-127 meV/cell) in the bilayer (bulk), depending on the
choice of vdW-DF version. We obtain the corresponding band diagrams using
calculations in the ordinary generalized gradient approximation for the
geometries specified by our vdW-DF results, so probing the indirect effect of
vdW forces on electron behavior. We find significant band-gap modifications by
up to -1.2 eV (+4.0 eV) in various regions of the Brillouin zone, produced by
the bilayer (bulk) formation.Comment: 11 pages, 7 figures, 2 tables, accepted for publication in Phys. Rev.
