Mode-Dependent Phonon Relaxation in fcc Ni: Insights from Molecular Dynamics Simulations with Frozen-Trajectory Excitations

We present a computational method and apply it to study phonon relaxation in face-centered cubic (fcc) nickel (Ni). The phonons are excited beyond their thermal equilibrium population, and the relaxation behavior is analyzed as a function of both the wave vector $\vec{q}$ and the phonon frequency $\omega$. To efficiently investigate these excitations, we introduce a trajectory post-processing technique, the frozen-trajectory excitation, which facilitates the $(\vec{q},\omega )$-resolved analysis. Molecular dynamics simulations combined with frozen-phonon multislice calculations predict relaxation signatures observable with time-resolved transmission electron microscopy (TEM) at 10–20 fs resolution. Our findings indicate mode dependence in the relaxation processes, highlighting the importance of considering phonon-specific behavior in ultrafast dynamics.