High-pressure melting of tantalum from the modified Z method

Abstract

We examined the validity of the modified Z method to predict the high-pressure melting curve of the body-centered-cubic transition metals, e.g., tantalum, in the molecular dynamics simulations using an extended Finnis-Sinclair potential. A unique feature was observed that a solid system evolves into the steady interphase of the solid and the liquid. In spite of simple running processes, the melting curve extracted from the solid-liquid coexistence states composed of only 960 atoms reaches an excellent agreement with that of the two-phase method in the literature. The liquid microstructure at the melting curve is dominated by the icosahedral short-range order, almost independent of the pressure up to 400 GPa.

Melting curves and structural properties of tantalum from the modified-Z method

“…For melting prediction, modified-Z method 15,16 proposed recently by Wang et al is selected, together with twophase simulation 30 and Z method 31,32 for comparison. In two-phase simulation, the initial simulation sample contains 12 Â 12 Â 24 bcc Ta unit cells, corresponding to 6912 atoms (two atoms in one unit cell).…”

“…For the M-Z method, the simulation processes are the same as those reported by Wang et al 15,16 Different from Z method, the simulation box is rectangular parallelepiped with L x ¼ L y ( L z instead of cubic. In our simulation, a box with 6 Â 6 Â 48 unit cells (3456 atoms) is applied.…”

“…To validate the scientific design and rational application, it is crucial to make the equation-ofstate of Ta well-informed. However, the melting curves of Ta, obtained from shock-wave compression, 3 DAC experiments, [4][5][6][7][8] and theoretical methods, [9][10][11][12][13][14][15][16][17][18] show great inconsistencies up to now.…”

“…V C 2015 AIP Publishing LLC 118, 235901-1 free energy method. 33 Recently, Wang et al 15,16 systematically summarized the four methods from the degrees of accuracy, empiricism, and complexity. They proposed that Z method is able to explain the physical meaning of the maximum superheating, but produces a melting curve slightly lower than two-phase simulation by taking the lowest temperature of liquid as melting point.…”

“…They proposed that Z method is able to explain the physical meaning of the maximum superheating, but produces a melting curve slightly lower than two-phase simulation by taking the lowest temperature of liquid as melting point. 15,16 Then, they proposed a modified Z (M-Z) method which allows one to obtain the melting temperature from solid-liquid coexistence state by introducing a rectangular parallelepiped simulation box (Lx ¼ Ly ( Lz). With their modified Z method, one can obtain a solid-liquid coexistence state, from which the melting point can be predicted more precisely.…”