Phonon Properties of Multi-layered Graphene from Molecular Dynamics Simulations
Résumé
In this work, we have studied the phonon properties of multi-layered graphene of 1-5L and Bulk Graphite(BG) from the analysis of Molecular Dynamics (MD) simulations, by employing the k-space AutocorrelationSequence (k-VACS) method. From the atomic trajectories and positions obtained from MD we calculate theVelocity Autocorrelation Function of the atoms in the system, which is then Fourier Transformed (FT) toobtain the phonon Spectral Energy Density Z(k, ω) [1]. From this we extract the temperature-dependence ofthe energies ω k,j (T ) and lifetimes τ k,j (T ), as well as the Phonon Densities of States (PDOS), for temperaturesranging from 80 K to 1000 K (see Fig. 1). We then focus on the impact of the number of layers N on theenergies ω(T ) and lifetimes τ (T ) of Γ-point phonons, as well as the type of interlayer potential used. Forthe later we used comparatively the Kolmogorov-Crespi (KC) [2] and the Lennard-Jones (LJ) potentials.We have found that the number of layers N has little effect on the energies ω of the intra-layer (ZO andE 2g ) modes and greater effect on the inter-layer ones (Layer Shearing and Layer Breathing) modes, while τis more sensitive to N for all modes. The effect of N on the lifetimes was also found to be independent of thetype of potential used, as for both the KC and the LJ interlayer potential, the lifetime of the Raman-activeG phonon increases with the number of layers N . In Fig. 1 (left) we present for illustration the temperaturedependence of the G phonon lifetime τ G (T ) obtained from MD, compared with DFT calculations [6] andexperimental data [7]. In this work we present, to the best of our knowledge, several findings for the firsttime: the T-dependence of ω(T ) for the intralayer modes and the effect of N on the lifetime τ G (T ) of theRaman-active G phonon.
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