Preparation of icosahedral gold cluster
A liquid gold sphere with 2624 atoms has been cooled down to 100K to obtain a faceted icosahedral gold cluster. The configuration of 900K has been heated up to 925K, 950K, 975K. That of 1000K has been heated up to 1010K, 1020K, ..., 1090K.
Caloric curve of potential energy and constant volume heat capacity
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The peak at 900K may due to supercooling.
Surface and multi-layer discrimination
Cone algorithm has been used to discriminate the surface atoms and divide the cluster into multi sub-surface layers. Multi-layer analysis shows the potential energy and bond order parameters for different layers.
Diffusion and surface melting
The movement of surface atoms ( characterized as maximal moving distance from the original place is larger than 6.1 Angstrom) starts at 600K first from the vertex, where atoms have less neighbors and thus easier to move around. Diffusion coefficients and number of moved atoms and their MSD/travel ratio (the ability of moving straightly) have been calculated.Although MSD calculation and visual examination shows that surface atoms travel very long distance at 1000K, multi-layer BOP calculations show that the surface structure doesn't change a lot. This may suggest that surface atoms travel around freely but still keeping the relative positions with neighbor atoms to form the icosahedral structure, which is different from liquid. In this sense we can not say surface is melted at 1000K.
However, if we define surface melting as the ability of traveling between layers, we may say surface starts to melt at 600K and completely melted at 1000K according to the layer-number calculation.
Flatness and bond curvature
Flatness and bond curvature have been calculated for 2624 atoms. Their distributions may reflect the faceting behaviour clearly, but More data (900K-1100K) are needed to pass the analysis.The configurations colored with bond curvatures show clearly vertex, edge and facet regions.
Local parabolic curvature
Local parabolic curvatures have been calculated for 2624 atoms. The configurations colored with larger parabolic curvature also illustrate the three regions.