▎ 摘　　要

In the framework of the Keating model with allowance made for the anharmonic constant of the central interaction between the nearest neighbors mu, analytical expressions have been obtained for three third-order independent elastic constants c (ijk) (mu, zeta) of single-layer graphene, where zeta = (2 alpha - beta)/(4 alpha + beta) is the Kleinman internal displacement parameter and alpha and beta are the harmonic constants of the central interaction between the nearest neighbors and the noncentral interaction between the next-nearest neighbors, respectively. The dependences of the second-order elastic constants on the pressure p have been determined. It has been shown that the moduli c (11) and c (22) differently respond to the pressure. Therefore, graphene is isotropic in the harmonic approximation, whereas the inclusion of anharmonicity leads to the appearance of the anisotropy.