Molecular dynamics simulation and thermodynamic model of vapor–solid coexistence of the Lennard–Jones fluid in cylindrical nanopores

Abstract Molecular dynamics (MD) simulations were used to study the coexistence of solids and vapors of Lennard–Jones methane condensed within cylindrical carbon nanopores. The simulated unit cell includes both the inside and outside of the pores. This allowed us to observe the solid–vapor coexistence within the pores while simulating the pressure depression of the bulk vapor outside the pores. The condensates in the pores were cooled in stages, and the equilibrium vapor pressures were determined at each temperature. The obtained vapor–solid coexistence curves showed significantly lower shifts in pressure than those in the bulk phase. The results of the MD simulations were compared with the Clausius–Clapeyron equation starting from the triple point in the nanopores. The thermodynamic model successfully predicted the simulation results without introducing tunable parameters, demonstrating this concept’s validity. Thus, a whole Lennard-Jones phase diagram in cylindrical nanopores can now be predicted.