Vibrational and thermodynamic properties of pure and gold adsorbed graphene

We investigate the effect of adsorbed gold atom on phonon dispersion curves of a graphene sheet and calculate various thermodynamic properties of pure and gold-adsorbed graphene using Ab initio density functional perturbation theory (DFPT). The phonon frequencies have been calculated using Vienna ab initio Simulation Package (VASP) software in combination with phonopy code in the harmonic approximation. The variation of concentration of gold has been simulated by placing one and two gold atoms on graphene sheets containing successively 8 C-atoms (G(8)) and 32 C-atoms (G(32)). From phonon dispersion curves, it is clear that the change in the phonon frequencies of graphene with 3.125% Au adsorbent (G(32)) is negligible as compared to 12.5% of Au adsorbent (G(8)). An increase in the variation of entropy as well as specific heat with temperature is also observed upon Au adsorption in both graphene sheets as compared to pure graphene. But reverse trend is observed for the case of variation of free energy with temperature. Here, it decreases upon Au adsorption.