Volume dependence of the transit contribution in the vibration-transit theory of liquids

Previously, we created a model for the transit contribution to the thermodynamic functions of a liquid [Phys.\ Rev.\ \textbf{E} 81, 041201 (2010)]. The model modifies the potential surface in which atoms in the liquid state move. The two parameters of the model are $\chi$, the maximum transit entropy, and $\theta_{\rm tr}$, a characteristic temperature near (but not equal to) the melt temperature. Using a combination of experimental data and density functional theory results, we calculate the volume derivatives of these parameters, thus giving the first-order volume dependence of the model.