  Clathrate hydrates are vital in energy research and environmental
applications. Understanding their stability is crucial for harnessing their
potential. In this work, we employ direct coexistence simulations to study
finite-size effects in the determination of the three-phase equilibrium
temperature ($T_3$) for methane hydrates. Two popular water models, TIP4P/Ice
and TIP4P/2005, are employed, exploring various system sizes by varying the
number of molecules in the hydrate, liquid, and gas phases. The results reveal
that finite-size effects play a crucial role in determining $T_3$. The study
includes nine configurations with varying system sizes, demonstrating that
smaller systems, particularly those leading to stoichiometric conditions and
bubble formation, may yield inaccurate $T_3$ values. The emergence of methane
bubbles within the liquid phase, observed in smaller configurations,
significantly influences the behavior of the system and can lead to erroneous
temperature estimations. Our findings reveal finite size effects on the
calculation of the $T_3$ by direct coexistence simulations and clarify the
system size convergence for both models, shedding light on discrepancies found
in the literature. The results contribute to a deeper understanding of the
phase equilibrium of gas hydrates and offer valuable information for future
research in this field.
