Features of the E 2 g phonon mode in MgB2

A model estimate of the energy eigenvalues of the E _2g phonon mode of the ion vibrations in the plane of boron atoms is obtained. It is shown that the anharmonic contribution to the energy of E _2g monotonously increases with the increase in z = A ₄/A ₂², where A ₄ is the fourth-order anharmonic coefficient and A ₂ is the harmonic constant. The results agree with the estimate in the Hartree-Fock approach. However, the discrepancy between these results and Raman spectroscopy data indicates the necessity to account for the influence of the electron-phonon interaction on the energy of E _2g in more detail. Original Russian Text ? V.V. Rzhevskii, 2009, published in Vestnik Moskovskogo Universiteta. Fizika, 2009, No. 1, pp. 93–94.