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Elucidating the Effects of Adsorbent Flexibility on Fluid Adsorption Using Simple Models and Flat-Histogram Sampling Methods



Vincent K. Shen, Daniel W. Siderius


Using flat-histogram Monte Carlo methods, we investigate the adsorptive behavior of the square-well fluid in two simple slit-pore- like models intended to capture fundamental characteristics of flexible adsorbent materials. The models require thermodynamic information about the flexible adsorbent material itself as input. An important component of this work involves formulating the flexible pore models in the appropriate thermodynamic (statistical mechanical) ensembles, namely the osmotic ensemble and a variant of the grand-canonical ensemble. Two-dimensional probability distributions, which are calculated by flat-histogram methods, provide the information necessary to determine the adsorptive properties. From these distributions, we are able to determine precisely adsorption isotherms, (equilibrium) phase transition conditions, limits of stability, and free energies for a number of different flexible adsorbent materials, distinguishable as different inputs into the models. While the models used in this work are relatively simple from a geometric perspective, they yield non-trivial adsorptive behavior, including adsorption-desorption hysteresis solely due to material flexibility and so-called ``breathing" of the adsorbent. The observed effects can in turn be tied to the inherent properties of the bare adsorbent. Some of the effects are expected on physical grounds while others arise from a subtle balance of thermodynamic and mechanical driving forces. In addition, the computational strategy presented here can be easily applied to more complex models for flexible adsorbents.
Journal of Chemical Physics


molecular simulation, statistical mechanics, thermodynamics, adsorption


Shen, V. and Siderius, D. (2014), Elucidating the Effects of Adsorbent Flexibility on Fluid Adsorption Using Simple Models and Flat-Histogram Sampling Methods, Journal of Chemical Physics, [online], (Accessed April 16, 2024)
Created June 24, 2014, Updated November 10, 2018