Effect of high pressure on the electron-phonon interaction and superconductivity in ZrN and HfN

Ab initio calculations of the superconducting properties have been performed for zirconium and hafnium nitrides at normal and high pressures. The results for ZrN are in good agreement with the existing data of the tunnel experiments and measurements of the pressure derivative of the critical temperature T _c. It has been shown that the decrease in T _c under compression occurs due primarily to an increase in the phonon frequencies.