January 21 2003

Diffusion coefficients for 2624 atoms (heating results for T>=1000K)

The results of diffusion coefficient and diffusion between layers both suggest the surface melting of this icosahedral system starts at a temperature between 500K and 600K. ( Can surface also be supercooled? If so, our cooling procedure may lowered this temperature. ) Surface melting seems to be a second-order transition.

Diffusion coefficients were collected by constant temperature MD simulations from the end point of corresponding Andersen thermostat simulations.

Mean square displacements for internal atoms

Mean square displacements for surface atoms

Diffusion coefficients

Diffusion between layers

Surface layer, four sub-surface layers and bulk were distinguished for the system at 5K (quenched by conjugate gradient minimization) and higher temperature configurations (100K-1400K, 100 configurations for each temperature level). The initial layer-numbers of atoms are define as:

Layer-number	Layer
0	Surface
1	Sub-layer 1
2	Sub-layer 2
3	Sub-layer 3
4	Sub-layer 4
5	Bulk

At each temperature, the layer-numbers of atoms were traced and averaged over 100 configurations. The right column is the results by defining the initial reference labels at the start point of each temperature level individually.