We present an ab initio pseudopotential study, within the local density functional approximation, of the structural and elastic properties of rock-salt TiC. The calculated structural and elastic properties of TiC are in good agreement with reported experimental values. Using the density-functional perturbation theory, the phonon spectrum and density of states are calculated. Good agreement has been found between the calculated and reported experimental dispersion curves. Following these bulk properties, we have made theoretical investigations of the atomic geometry and lattice dynamics of the TiC͑001͒͑1 ϫ 1͒ surface. The calculated surface structural parameters compare very well with available experimental values. Using our calculated surface phonon spectrum, we provide a detailed analysis of available experimental data from electron energy-loss spectroscopy.
Structural, elastic and dynamical properties of the rock-salt HfC have been studied by employing an ab initio pseudopotential method and a linear response scheme, within the generalised gradient approximation. In addition to achieving good agreement with experimental measurements of the phonon dispersion results along the symmetry direction À-X, we have presented accurate dispersion results along several other directions in the Brillouin zone. Sharp features in the phonon density of states are ascertained and their origin discussed. This is followed by investigations of the structural, electronic and phonon properties of the HfC(001) surface. The agreement between our surface phonon spectrum and experimental measurements is very good. By analysing the atomic displacement patterns of the zone-centre and zone-edge phonon modes we have determined the energy locations and polarisation characteristics of Fuchs-Kliewer, Wallis, Lucas and Rayleigh modes.
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