Determination of Hydroquinone Clathrate Stability for Different Guest Molecules Using NPH Ensemble Molecular Dynamics

Clathrates are crystalline compounds with a wide range of applications, particularly in the fields of storage of substances of interest (such as hydrogen) and gas separation. In this work, molecular dynamics simulations are used to investigate the stability of β-hydroquinone clathrates (HQ clathrates) containing guest molecules such as Ar, CH₄, H₂, and CO₂ in a pressure range between 100 and 1000 bar. To this end, the isobaric-isenthalpic (NPH) ensemble was used, which allows the equilibrium conditions to be studied without applying artificial temperature control, providing a direct and more realistic view of the thermodynamic response of the system. Atomistic models based on the OPLS-AA force field are used for this purpose. The results reveal a tendency for the coexistence temperature to increase with pressure, which is more pronounced for larger, apolar guests (Ar and CH₄) compared to smaller, polar species (H₂, CO₂). This study represents the first application of the NPH-based methodology to organic clathrates, demonstrating its effectiveness in studying the limiting thermodynamic conditions associated with phase transitions. The findings presented provide a solid theoretical framework for understanding the dynamic behavior of HQ clathrates and open up new perspectives for their use in the safe and reversible storage of hydrogen.