(629b) Interrogating Simple Pore Models Using Flat-Histogram Sampling Methods to Understand the Effect of Sorbent Flexibility On Fluid Adsorption

While it is well known that sorbent flexibility can affect observed adsorption behavior, rigid sorbents are still commonly used in the study of adsorption via molecular simulation for both simplicity and practicality. Past attempts at incorporating sorbent flexibility in simulation have largely relied on computationally demanding atomistic descriptions of the sorbent framework. In this work, we present two simple pore models for flexible sorbents. The first model accounts for internal sorbent flexibility in a grand canonical ensemble formulation. The second model accounts for volume fluctuations via an osmotic ensemble formulation. In both cases, we use flat-histogram sampling methods to calculate precisely the relevant multi-dimensional probability distributions, which we will show are directly related to specific thermodynamic potentials and the deformation properties of the sorbent. Using a square-well fluid as the adsorbate, we are able to reproduce experimentally observed adsorption behavior, such as adsorption-induced deformation and breathing phase transitions. More importantly, we are able to identify the physically relevant features (or properties) of the sorbent that lead to these interesting and exploitable sorbent properties.