Melting line of aluminum from simulations of coexisting
phases
J. R. Morris, C. Z. Wang, K. M. Ho, and C. T. Chan
Phys. Rev. B 49, 3109 (1994)
Abstract
We have performed simulations of coexisting liquid and solid
phases of an embedded atom model of aluminum as an efficient way of mapping out
the coexistence line. This technique is convenient, as it does not require
complicated free energy calculations for the different phases, but simply allows
the system to equilibrate to a coexistence point. By altering the simulation
volume and/or energy, a new coexistence point is found. The calculated melting
temperature is lower than previous results for the identical model; we suspect
that this difference is due to the difficulty of calculating the free energy of
the liquid phase, leading to inaccuracies in the previous work. A thorough
examination of several different system sizes, from 1024 to 65,536 particles,
indicates that the results are only weakly dependent upon the system size.
(A simple movie
demonstrating the simulation of coexisting phases is available here.)
In the figure below, we show a snapshot picture of the system with coexisting
phases. The atoms which were originally in the solid phase are indicated in
blue, while the atoms that began in the liquid phase are shown in orange. The
system has partially crystallized in order to reach equilibrium at the melting
temperature.
Below we show the pressure-temperature phase diagram. The different points
represent different simulations. Different symbols indicate the number of atoms
used in the simulation, including 1024 (open circles), 4096 (solid squares),
8192 (solid triangles), and 65536 (solid hexagon, near P=0). The solid line is a
fit of the N=1024 results to the form T=T(0)+aP+bP^2; the P=0 melting
temperature is found to be T=724 K.
