Structure and dynamics of NiO 001/ and NirNiO 001/ surfaces by molecular dynamics simulation

Using molecular dynamics and a rigid ion potential, we studied the vibrational and structural properties of the NiO 001. surface with and without cationic adatoms. We found that the bulk phonon density of states DOS.is altered by the presence of the surface and that the adatom introduces new frequency modes. From the relaxed positions of the surface ions, it came out that up to 0.7Tm, the surface is contacted exhibiting rippling with outwards expansion of the cations and inwards contraction of the anions. The effect is detectable in five layers below the surface, while it persists at high temperatures. Strong contraction is found for the cationic adatom, relaxing on top of a surface anion that is lifted by more than 30% from its equilibrium position at high temperatures. q2000 Elsevier Science B.V. All rights reserved.