Dynamics of melting argon clusters

With increasing total energy, small atomic clusters show a smooth transition from a rigid solidlike to a floppy liquidlike ''phase.'' In certain clusters, depending on their structure and stability, this transition takes place over a finite energy range where both these ''phases'' coexist in a dynamical sense, whereas in others the transition does not involve a coexistence region and has been called ''slushlike.'' Previous studies in Ar-13, which belongs to the first kind, have established the energy variation of maximal Lyapunov exponent (MLE) and the dynamic structure factor (DSF) as ''dynamical indicators'' of this transition. To understand the general features of these dynamic indicators better, we investigated the dynamic properties of two clusters Ar-19 and Ar-17. The former is a magic number cluster whose behavior is expected to be similar to Ar-13, whereas the latter which does not show a coexistence region belongs to the second kind. Ar-19 shows a behavior similar to Ar-13. In Ar-17, we find that above the transition but close to it, the DSF still shows features exhibiting the interplay of a ''hot solid'' and a ''cold liquid'' as observed in the coexistence region of Ar-13 and Ar-19. Unlike the bond length fluctuation which exhibits a rapid increase near the transition, the behavior of MLE is rather smooth and it does not serve as a good dynamical indicator of the transition in the Ar-17 system.