Molecular dynamics study of one component soft-core system - Analytical expression of non-equilibrium relaxation in constant pressure conditions

• Analytical expressions were derived for non-equilibrium relaxations of the softcore (SC) model under the constant pressure condition for the first time.
• Molecular dynamics (MD) simulations were used to confirm the expressions and results are mapped on the phase-diagram.
• An important role of paths and fluctuations on the phase-diagram in the glass transition is shown.

Analytical expressions of non-equilibrium relaxation for the system with soft-core (SC) potential under the constant pressure condition (using the Andersen method) were derived for the first time and validity of them was confirmed by molecular dynamics (MD) simulations. The path of relaxations can be mapped on the phase-diagram (Compressibility factor g⁎ plotted against the reduced density ρ⁎) using its instantaneous value gt⁎ and is found to be a unique function of the reduced density, ρ*. Contribution of internal energy term to the NPH relaxation is found to be about 1/4 of the instantaneous compressibility factor, g(ρt⁎). It is also shown that different extended conditions resulted in different paths on the phase-diagram. Based on these results, a role of the path and fluctuations on the glass transition is discussed. Further details such as fluctuation of each term of thermal properties and effects of mass of walls are examined to serve a fundamental knowledge of the non-equilibrium relaxation.