Pressure dependence of the melting mechanism at the limit of overheating in Lennard-Jones crystals

We study the pressure dependence of the melting mechanism of a surface free Lennard-Jones crystal by constant pressure Monte Carlo simulation. The difference between the overheating temperature $\left(T_{\mathit{OH}}\right)$ and the thermodynamical melting point $\left(T_M\right)$ increase for increasing pressure. When particles move into the repulsive part of the potential the properties at $T_{\mathit{OH}}$ change. There is a crossover pressure where the volume jump becomes pressure independent. The overheating limit is preannounced by thermal excitation of big clusters of defects. The temperature zone where the system is dominated by these big clusters of defects increases with increasing pressure. Beyond the crossover pressure we find that excitation of defects and clusters of them start at the same temperature scale related with $T_{\mathit{OH}}$.

Figure 1

(a) Atomic volume (square, left-hand scale) and internal energy (circles, right-hand scale) vs the temperature $\left(T\right)$ for pressure $P=1000$, (b) the overheating temperature $\left(T_{\mathit{OH}}\right)$ as a function of the pressure. We also include the melting point $T_M$ as obtained in Ref. 13 (open diamond) and from Ref. 12 (stars). Dashed (dotted- dashed) lines correspond to the power law fitting given in Eq. (1) [Eq. (2)] shown in the text.

Figure 2

(a) The atomic volume of the solid $\left(v_{\mathit{OH}}\right)$ at the overheating limit as a function of $P$ (dashed line, square symbols). The solid line shows the volume where $G^{\prime }$ vanishes at $T=0$. We also include the volume at the melting point $\left(v_M\right)$ extracted from Ref. 12 (dotted-dashed line, diamonds). The inset shows the volume dependence of the cohesive energy of an ideal fcc crystal. The dashed (solid) arrow signal the thermal energy to melt (overheat) the crystal. (b) The percentage jump of the atomic volume at the overheating limit.

Figure 3

The two terms of the Clausius-Clapeyron equation evaluated numerically. The solid line corresponds to $d{T}_{\mathit{OH}}∕dP$ evaluated from Eq. (2). Squares correspond to $T_{\mathit{OH}}\Delta v∕L_h$ where the latent heat $L_h$ is obtained from the jumps of the internal energy and the volume $\left(\Delta v\right)$.

Figure 4

The percentage of defects (left-hand scale) and the mean coordination number (right-hand scale) as functions of the reduced temperature for different pressures.

Figure 5

The average number of clusters as a function of $\overline{T}$ for different pressures.