Crystal Structures and Electronic Properties of Single-Layer, Few-Layer, and Multilayer GeH

Single-layer germanane (GeH) structures have been explored using evolutionary algorithms combined with first-principles methods. The chair GeH is the most stable structure among all uncovered single-layer GeH structures, which is similar to what is found in graphane. Multilayer and few-layer GeH structures with 2-6 layers in their unit cells are constructed from the chair GeH in various possible stacking sequences. Many isoenergetic multilayer GeH structures are found using the semiempirical dispersion correction of DFT-D3. It is shown that the experimentally synthesized bulk GeH [ Bianco et al. ACS Nano 2013, 7, 4414 ] assumes the tr6 structure, not the previously claimed 2H structure. Band structure calculations reveal that the location of the direct band gap of multilayer GeH structures oscillates between the Γ and A point in their first Brillouin zone depending on whether the unit cell contains an odd or even number of layers. The band gaps of multilayer and few-layer chair GeH structures are calculated to lie between 1.47 and 1.66 eV using the hybrid HSE06 functional, and they are dependent on the stacking sequences and interlayer distances.