Vibrational and topological properties of selected NiO surfaces

We present a study of the vibrational properties of the (1 0 0) and (1 1 0) surfaces of nickel oxide. We performed molecular dynamics simulations over a wide temperature range and we calculated the phonon local density of states (LDOS) of the anionic and cationic sublattices as a function of the distance of the atomic planes from the surface. We discuss the differences observed at T = 300 K in the phonon LDOS compared to the bulk as well as the differences observed among the two surfaces due to their specific atomic structure. As far as the temperature behavior of the phonon LDOS is concerned for the (1 0 0) surface we have preservation of its main characteristics up to high temperatures while for the (1 1 0) a modification of the phonon LDOS is observed above T = 1000 K. The difference in behavior of the two surfaces is related to the stability of the (1 0 0) surface and the modification of the atomic structure of the surface planes of the (1 1 0) surface above T = 1000 K.