Surface phonons on the NbC(001) and TaC(001) surfaces

Structural, electronic, and vibrational properties of NbC(001) and TaC(001) are presented, based on the application of plane-wave basis, pseudopotentials, and the generalized gradient approximation of the density functional scheme. In agreement with previous theoretical and experimental studies, the rippled relaxation of these surfaces is observed. Both surfaces show metallic character due to a partially filled band. The calculated phonon-dispersion relations for both surfaces accord very well with the available experimental data. Energy locations and polarization characteristic of Rayleigh, Love, Wallis, Lucas, and Fuchs-Kliewer modes have been determined. Our results reveal that due to symmetry lowering the electron-phonon interaction on these surfaces is much weaker than the corresponding interaction in their bulk form.