(525i) Hybrid MD/MC Simulations of Adsorption on Flexible Nanoporous Materials

Nanoporous materials are known to deform upon the adsorption of guest molecules. This occurs due to the stress exerted by the guest molecules on the framework atoms resulting in the expansion or contraction of the adsorbent structure. To gain theoretical insights into this phenomenon, various simulation techniques have been developed including the osmotic ensemble method and the hybrid MD/MC simulations. The hybrid osmotic ensemble involves running short molecular dynamics simulations in the NPT ensemble as an additional Monte Carlo move in the grand canonical ensemble. On the other hand, the hybrid MD/MC requires switching between the GCMC and NPT MD simulations until the convergence is reached. In this study, we explore the differences between these two approaches using methane adsorption on IRMOF-1 as an example.

We conducted the osmotic ensemble simulations using RASPA and the hybrid MD/MC simulations using LAMMPS. Additionally, we compared the isotherms on the flexible structures with those obtained by the GCMC simulations on rigid structures and explain the observed differences, see Figure. Finally, we discuss an optimal balance between the numbers of MD and MC moves to achieve a faster convergence. Although the hybrid simulations have shown promise in flexible materials, a significant challenge that remains is the requirement for a precise flexible forcefield that can effectively reproduce the experimental isotherms.

This work is supported by the NSF CBET grant 1834339.