  We carry out density-functional ab initio molecular dynamics (AIMD)
simulations of Ti adatom (Tiad) migration on, and descent from, TiN
<100>-faceted epitaxial islands on TiN(001) at temperatures T ranging from 1200
to 2400 K. Adatom-descent energy-barriers determined via ab initio
nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer
transport on TiN(001) occurs essentially exclusively via direct hopping onto a
lower layer. However, AIMD simulations reveal comparable rates for Tiad descent
via direct-hopping vs. push-out/exchange with a Ti island edge atom for T >=
1500 K. We demonstrate that the effect is due to surface vibrations, which
yield considerably lower activation energies at finite temperatures by
significantly modifying the adatom push/out-exchange reaction pathway.
