Abstract
The pressure dependences of the crystallographic parameters of the γ-InSe structure in the range up to 15 GPa are theoretically investigated using the density-functional method. It is established that, in the range from 7 to 11 GPa, the pressure dependences of the lattice parameters exhibit an anomalous behavior: the rigidity of the lattice increases in the direction of the weak bond and decreases in the plane of the layers. The layer thickness is characterized by a nonmonotonic pressure dependence. The numerical values of the lattice parameters of the crystal structure under compression are determined, and the pressure dependences of the vibrational frequencies at the center of the Brillouin zone are calculated theoretically. The results of the theoretical calculations are in good agreement with the available experimental data.

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