Rationalizing the role of structural motif and underlying electronic structure in the finite temperature behavior of atomic clusters

Abstract

Melting in finite size systems is an interesting but complex phenomenon. Many factors affect melting and owing to their interdependencies it is a challenging task to rationalize their roles in the phase transition. In this work, we demonstrate how structural motif of the ground state influences melting transition in small clusters. Here, we report a case with clusters of aluminum and gallium having same number of atoms, valence electrons, and similar structural motif of the ground state but drastically different melting temperatures. We have employed Born-Oppenheimer molecular dynamics to simulate the solid-like to liquid-like transition in these clusters. Our simulations have reproduced the experimental trends fairly well. Further, the detailed analysis of isomers has brought out the role of the ground state structure and underlying electronic structure in the finite temperature behavior of these clusters. For both clusters, isomers accessible before cluster melts have striking similarities and does have strong influence of the structural motif of the ground state. Further, the shape of the heat capacity curve is similar in both the cases but the transition is more spread over for Al36 which is consistent with the observed isomerization pattern. Our simulations also suggest a way to characterize transition region on the basis of accessibility of the ground state at a specific temperature.

Multifaceted Thermodynamics of Pbn (n = 16–24) Clusters: A Case Study

“…It is interesting to note that such a partial/ characteristic similarity of atomic clusters with Jellium has been previously seen in clusters of gallium and of aluminum. 32,55 Thus, similarity of "MOs formed out of atomic s" with those of the Jellium orbitals is not just Pb specific but seems to be a trait common to other small clusters in general.…”

“…One cannot ignore the trends in global minimum energy structures (GS) of small clusters while explaining their thermodynamics, because their GS structures sit at the center stage, when it comes to explaining their finite temperature behavior. − It has been demonstrated for gallium as well as aluminum clusters that variation in the structural motif of the GS and melting temperatures are correlated. , It must be noted, however, that although it is not possible to explain the liquid-like state of clusters from their GS structures, their behavior until the point of isomerization and before melting is closely related to their GS for clusters with few tens of atoms . Another example could be elements Si and Sn, belonging to group IV-A, which exhibit fragmentation of their clusters with increasing temperature. ,,, A possible reason for such behavior could be the covalent type bonding among atoms of these elements, which leads to formation of locally bonded, more stable smaller subunits at finite temperatures.…”

“…30,33 It must be noted, however, that although it is not possible to explain the liquid-like state of clusters from their GS structures, their behavior until the point of isomerization and before melting is closely related to their GS for clusters with few tens of atoms. 32 Another example could be elements Si and Sn, belonging to group IV-A, which exhibit fragmentation of their clusters with increasing temperature. 15,16,19,22 A possible reason for such behavior could be the covalent type bonding among atoms of these elements, which leads to formation of locally bonded, more stable smaller subunits at finite temperatures.…”

Combining DFT with ML to study size specific interactions between metal clusters and adsorbates

“…The GS geometries for all the clusters were taken from previously reported work. [71][72][73][74] As shown in Fig. 1, the adsorbate was kept along the outward radial vector from center of mass of the cluster to surface atom.…”