Vibrational modes and diffusion of self-interstitial atoms in body-centered-cubic transition metals: A tight-binding molecular-dynamics study

Using a tight-binding molecular-dynamics method, we have calculated the formation energies, diffusivity, and localized vibrational frequencies of self-interstitial atoms (SIA's) in body-centered-cubic (bcc) transition metals: vanadium, niobium, molybdenum, and tantalum. As a test of our methods, we compare to experiment for the perfect bcc phonon spectra and we compare to previous ab initio SIA formation energies. In addition, we present vibrational spectra calculated from molecular dynamics via the velocity autocorrelation method. For all of the systems studied, we find that the localized vibration frequency of a SIA dumbbell pair is roughly twice the frequency of the bcc phonon-density-of-states peak. We also find an Arrhenius temperature dependence for SIA hopping, with frequency prefactors ranging between the cutoff of the ideal bcc lattice and the highest frequencies of the SIA dumbbell. In all cases, we find that the energy barrier to SIA diffusion is approximately 0.1 eV.