**Ti adatom diffusion on TiN(001): Ab initio and classical molecular
dynamics simulations**

DG Sangiovanni and D Edstrom and L Hultman and I Petrov and JE Greene and V Chirita, SURFACE SCIENCE, 627, 34-41 (2014).

DOI: 10.1016/j.susc.2014.04.007

Ab initio and classical molecular dynamics (AIMD and CMD) simulations
reveal that Ti adatoms on TiN(001) surfaces migrate between neighboring
fourfold hollow sites primarily along in-plane <100> channels. <100> and
<110> single jumps, as well as <100> double jump rates, obtained
directly from MD runs as a function of temperature, are used to
determine diffusion activation energies Ea, and attempt frequencies A,
for the three preferred Ti adatom migration pathways on TiN(001). From
transition rates Aexp**-Ea / (k(B)T)**, we determine adatom surface
distribution probabilities as a function of time, which are used to
calculate adatom diffusion coefficients D(T). AIMD and CMD predictions
are consistent and complementary. Using CMD, we investigate the effect
on the adatom jump rate of varying the phonon wavelength degrees of
freedom by progressively increasing the supercell size. We find that
long-wavelength phonons significantly contribute to increasing adatom
mobilities at temperatures <= 600 K, but not at higher temperatures.
Finally, by directly tracking the Ti adatom mean-square displacement
during CMD runs, we find that Ti adatom jumps are highly correlated on
TiN(001), an effect that yields lower D-s values (D-s(corr)) than those
estimated from uncorrelated transition probabilities. The temperature-
dependent diffusion coefficient is D-s(corr) (T) = (4.5 x 10(-4) Cm-2
s(-1)) exp**-0.55 eV / (k(B)T)**. (C) 2014 Elsevier I3.V. All rights
reserved.

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