VIBRATIONAL AND STRUCTURAL PROPERTIES OF THE NB (001) SURFACE WITH AND WITHOUT A NB ADATOM BY TIGHT-BINDING MOLECULAR DYNAMICS

摘要

We present results of tight-binding molecular dynamics simulations of the Nb(001) surface. We find that the surface energies of the unrelaxed and relaxed system are in good agreement with the available experimental and theoretical data. From the calculated phonon density of states, we found that the bulk phonon mode around 6.4 THz is altered by the presence of the surface, indicating looser coupling between the surface and the bulk atoms. Furthermore, it emerges that the surface atoms are more tightly bound in the direction normal to the surface than in the in-plane directions. We find that a Nb adatom exhibits a contraction, while from its phonon density of states, it appears to be more tightly bound in the direction normal to the surface, introducing modes at higher frequencies than those of surface atoms. From these results, we conclude that our method reproduces satisfactorily the main features of the Nb (001) surface and that it is a promising approach for describing this class of materials.