Vibrational dynamics and thermodynamics of Ni(977)

Abstract

A molecular dynamics study of the thermodynamic properties of liquid Ni using the Voter and Chen version of the embedded atom model

Temperature dependence of atomic relaxation and vibrations for the vicinal Ni(977) surface: a molecular dynamics study

“…Since experimental data for surface phonon frequencies [3] and another theoretical calculation [9] are available on Ni(9 7 7), in this paper we use the MD method and MAEAM potential to calculate the temperature dependence of the surface relaxation, phonon spectrum, mean square displacement of atoms, and the layer structure factor for the stepped (9 7 7) surface of Ni up to 1700 K, which is only 60 K below the bulk melting point. Present calculation is carried out for much higher temperature than real space GreenÕs function approach [9].…”

“…This method provides the information about the surface phonon density of states and permits a clear discrimination for the surface localized modes and surface resonances. Using the GreenÕs function method with the EAM potential, Rahman and coworkers [9,10] calculated the local vibrational densities of (9 7 7) for Ni and (2 1 1), (3 3 1), (5 1 1) for Cu. In addition to phonon frequencies, the GreenÕs function has also been used to calculate the mean square vibrational amplitude of atoms, the surface specific heat and other thermodynamic quantities.…”

Are Vicinal Metal Surfaces Stable?

“…The reduced coordination of the step atoms on a vicinal surface makes the average vibration amplitude of vicinal surface atoms significantly higher than the vibration amplitude on low-index surfaces [23][24][25]. As a consequence, the excess vibrational entropy of a vicinal surface is higher than that of the corresponding low-index facet combination.…”

“…In the case of faceting, all steps are brought together to form a (111) terrace, and the step-free remainder of the surface has the (100) orientation. We assume for simplicity that the surface atoms are harmonic, isotropically vibrating Einstein oscillators, and that the step atoms on the (n11) surface have a vibration amplitude s step that is 20% higher than that on the (111) surface, s ͑111͒ [23][24][25]. The other atoms at the (n11) surface are assumed to have the same vibration amplitude as the terrace atoms on the (100) surface [25].…”

“…As a consequence, the excess vibrational entropy of a vicinal surface is higher than that of the corresponding low-index facet combination. For a proper calculation of the differences between the excess entropies, the full vibrational energy spectrum has to be computed for each of the surface orientations involved [23,24]. Here, we give only a simple estimate of the effect for a surface with the (n11) orientation.…”