The alternative description of the qtz C 6 structure (space group P6 5 22, No. 179 with unique (6a) sites ) is possible in space group P6 4 22, No. 181 with two distinct Wyckoff positions, namely (3c) and (3d), as shown in Table . Such a configuration corresponds to the binary equiatomic phosphides BP and AlP. The lattice parameters of the ground state structures are given in Table .