Ab initio simulation of graphane polymorphs

Abstract

The crystal and electronic structure, as well as the energy characteristics of seventeen polymorphic varieties of graphene layers functionalized by hydrogen, were calculated ab initio by the density functional theory method in the generalized gradient approximation. Polymorphic varieties of graphane were theoretically modeled as a result of chemical adsorption of hydrogen on the surface of graphene layers L6, L4-8, L3-12, L4-6-12 and L5-7. On the basis of each of these varieties of graphene, it is possible to form five, six, one, three and two structural types of graphane, respectively. Out of the 17 theoretically constructed graphane polymorphs, 16 have a stable structure. The structure of the СH-L4-8-T3 layer collapsed during geometry optimization. The structure of graphane layers differs by a different degree of deformation, characterized by the Def parameter. The minimum value of this parameter is 10.95° (СH-L6-T1 layer) maximum is 92.51° (СH-L4-8-T2 layer). The sublimation energy of graphane layers varies in the range from 10.70 to 11.48 eV/(CH). A linear dependence of the sublimation energy on the degree of deformation of the layer structure is observed: the less the layer is deformed, the higher its sublimation energy. The electronic structure of all studied graphane polymorphs has a band gap at the Fermi energy level. The width of the band gap varies from 4.76 (СH-L6-T1 layer) to 6.46 (СH-L4-8-T2 layer) eV. A clear dependence of the electronic characteristics on the values of the structural parameters for graphane layers could not be established.