Finite size effect on the existence of the liquid–vapour spinodal curve

Abstract

Fluids interacting with Lennard-Jones and Square Well potentials reach thermodynamic equilibrium forming two coexisting phases when simulated within the liquid–vapour spinodal region. If molecular dynamics simulations in the NVT ensemble are performed on a fluid kept in a cubic cell with periodic boundary conditions, liquid and vapour phases at equilibrium are separated by a process of spinodal decomposition. In the vapour side of the spinodal curve, spherical, cylindrical, and slab type liquid structures are formed, depending on the total density. Under the mentioned conditions, in the liquid side of the spinodal, vapour bubbles with the same shapes, surrounded by liquid, are formed. Results from this work suggest that as the simulation system size increases, the spinodal curve approaches the orthobaric, but it converges to a position closer to the coexistence curve but separated from it. The same thing happens for both potential models simulated. This is in sharp contrast with previous findings by Errington, McDowell, Binder and coworkers, where they conclude that ‘Only for infinitely large systems does the effective spinodal density converge to the macroscopic coexistence vapor density.’

GRAPHICAL ABSTRACT

Keywords:

• Spinodal curve
• finite size effects
• molecular dynamics simulation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

Thanks to Conacyt for the grant of Frontiers of Science No.2015-02-1450 entitled ‘Programmable Matter’, SEP-CONACYT-178963, RTMCB-2017 and for the scholarship support of (ABG). Also to the ‘División de CBI’ for grant PAPDI2021-001. Thanks also to the Super Computer Center of UAM-Iztapalapa for a generous allotment of computing time.