Among the group IV elemental monolayers, graphene has planar structure and other elemental monolayers such as silicene and germanene form a buckled structure. Theoretical studies have shown that group IV-VI binary monolayers, which are the counterparts of phosphorene may have both black and blue phases with puckered and buckled structures, respectively [45, 48, 65, 66]. Thus, two geometrical arrangements are taken into account for SiSe monolayers as puckered and buckled structures. The buckled and puckered structures are referred to as blue and black SiSe monolayers, respectively. First, using structural optimizations, the structural properties of the black and blue SiSe monolayers are computed. The atomic structures of blue and black SiSe monolayers and corresponding first Brillouin zone are shown in Figs. 1 and 2, respectively. The blue monolayer has one Si atom and one Se atom per unit cell. The Si atoms and Se atoms are connected to each other and they are arranged alternately at different heights to create a hexagonal buckled structure, similar to silicene and germanene. The lattice constant, Si-Se bond length, and buckling height after optimization are computed as 3.53 Å, 2.49 Å, and 1.42 Å, respectively.
