Order parameter by instantaneous normal mode analysis for melting behaviour of cluster Ag₁₇Cu₂

We perform isothermal Brownian-type molecular dynamics simulations with the Gupta potential for bimetallic cluster Ag₁₇Cu₂ from T=0 to 1500K, across the temperature range associated with the melting behaviour determined by the specific heat of the cluster. We also use the instantaneous normal mode (INM) analysis to dissect dynamics of the cluster. In terms of the projected density of states of the vibrational INMs, we propose a new order parameter that specifically describes the melting behaviour of the cluster. The calculated result of our order parameter is consistent with the information inferred from the specific heat data.