Nanoscale thermal stabilization via permutational premelting

Abstract

Anomalous higher-than-bulk melting in some metal clusters has been previously ascribed to particularly compact cluster structures and emergent covalent bonding at small sizes. Using both classical and ab initio molecular dynamics incorporating realistic interacting atomic environments, we show a MgO cluster which, although structurally flexible and with bulklike ionic bonding, melts at a higher temperature than rock salt MgO. We propose that this unexpectedly high thermal stability is due to the premelted dynamics of a bi-isomeric fluxional state allowing facile permutation of ion positions, raising the configurational entropy and lowering the free energy. We argue that this entropic stabilizing effect could also occur in other (nano)systems which allow for atomic permutations with relatively little structural change.

2D covalent triazine framework: a new class of organic photocatalyst for water splitting

“…42 The vacuum level was taken as the reference in the calculations of band alignment (VBM and CBM). Moreover, an ab initio molecular dynamics (AIMD) simulation was implemented to analyze the stability of the CTF structures under room temperature, which is a common procedure in AIMD following the method of Viñes et al 44 The initial conguration was given by the experimentally characterized structures and then le free to relax. Moreover, an ab initio molecular dynamics (AIMD) simulation was implemented to analyze the stability of the CTF structures under room temperature, which is a common procedure in AIMD following the method of Viñes et al 44 The initial conguration was given by the experimentally characterized structures and then le free to relax.…”

Concepts, models, and methods in computational heterogeneous catalysis illustrated throughCO2conversion

“…The lack of bonds between cluster atoms and those that exist in the material, which are neglected in the model, leads to a significant number of low‐coordinated atoms with concomitant high‐in‐energy electronic structures. Indeed, this instability is the driving force toward large structural deformations when the atomic structure of such a cluster model is fully optimized, particularly fostered by the large number of low lying structural isomers that exist in a narrow energy range, which are normally achievable through low energy barriers, pointing out their fluxionality 28,31 . To avoid these problems the structure of the cluster models is normally kept as in the catalyst structure, often at the bulk experimental or theoretical optimized positions 32 .…”

“…Indeed, this instability is the driving force toward large structural deformations when the atomic structure of such a cluster model is fully optimized, particularly fostered by the large number of low lying structural isomers that exist in a narrow energy range, which are normally achievable through low energy barriers, pointing out their fluxionality. 28,31 To avoid these problems the structure of the cluster models is normally kept as in the catalyst structure, often at the bulk experimental or theoretical optimized positions. 32 A different situation appears when one pretends to model larger systems, such as large nanoparticles (NPs), allowing for the versatile description of regular surface sites and even defective sites, such as corner, edge, step, or kink sites (see Figure 2(a)).…”

Trends in the adsorption and reactivity of hydrogen on magnesium silicate nanoclusters

“…13 we show various typical snapshots of the structures of the two clusters from these calculations. Although not a rigorous criterion, it is most likely that misleading large values of d occur through pre-melting effects 36 rather than a small d values incorrectly pointing to non-melting. We note that the appearance of bond being broken or formed in the snapshots is largely due to arbitrary bond length cut-offs in the visualisation rather than any true chemical re-ordering.…”