Modified Lennard-Jones potentials for Cu and Ag based on the dense gaslike model of viscosity for liquid metals

Based on the dense gaslike model of viscosity, we have obtained the modified Lennard-Jones potentials suitable for studying the liquid structure of Cu and Ag. Experimental data considered in deriving the potentials include the liquid density, viscosity, and pair correlation function. The energy and structural properties of liquid Cu and Ag in cooling processes have been studied via molecular dynamics simulations, exhibiting correct trends as a function of temperature. Calculated results are comparable with those derived by Johnson’s embedded-atom method (EAM) and effective pair potential. The differences between potential energy derived by pair potentials and calculations from EAM model may be attributed to the neglect of the electron background energy in pair potentials. The results also reveal that the uncertainty of experimental data affects greatly the accuracy of the pair potential.

Figure 1

(Color online) The viscosities of the liquid Cu and Ag. The solid and broken curves are the calculated results for each set of experimental data. The experimental data in Refs. 24, 25 are denoted by the mark of (×) and (+), respectively; the calculated results used in the Born-Green formula Eq. (18) are indicated by the mark of (엯) and (◻).

Figure 2

(Color online) The pair potentials of the liquid Cu and Ag. The solid and broken curves in (a) are the obtained results Cu and ${\mathrm{Cu}}^{*}$, respectively. The squares, circles and triangles correspond to other theoretical potentials in Refs. 2, 12, 16, respectively.

Figure 3

(Color online) The calculated and experimental pair correlation functions of liquid Cu and Ag.

Figure 4

(Color online) The calculated and referenced equation of states at $300\mathrm{K}$ for Cu and Ag.

Figure 5

(Color online) The energy and structural transitions of liquid ${\mathrm{Cu}}^{*}$. (a) potential energies for heating and cooling cycles; (b) results of potential energy derived by the current pair potential (squares), Johnson’s EAM model (circles) and effective pair potential (triangles), respectively; (c) PCF; (d) variation of the fractions of HA indices.

Figure 6

(Color online) The energy and structural simulations of liquid Cu upon cooling. (a) Potential energies for heating and cooling cycles; (b) PCF; (c) variation of the fractions of HA indices.

Figure 7

(Color online) The temperature dependence of energy and structure in liquid Ag in the process of cooling. (a) Potential energies for heating and cooling cycles; (b) PCF; (c) variation of the fractions of HA indices.