Probing gas adsorption in MOFs using an efficient ab initio widom insertion Monte Carlo method.

Area of Science:

• Computational Chemistry
• Materials Science
• Chemical Engineering

Background:

• Accurate computation of gas adsorption properties in porous materials is crucial for applications like gas storage and separation.
• The Henry coefficient (K_H) describes gas uptake at low pressures, but its calculation can be computationally intensive.
• Existing methods often require extensive simulations, limiting their practical application.

Purpose of the Study:

• To develop a novel, efficient method for calculating the Henry coefficient (K_H) of gas molecules in porous materials.
• To validate the proposed method using Density Functional Theory (DFT) calculations.
• To assess the reliability of DFT binding energy and heat of adsorption as predictors for Henry regime adsorption.

Main Methods:

• Implementation of a biased Widom insertion technique by partitioning the simulation volume into strongly and weakly adsorbing regions.
• Selective biasing of insertion moves into strongly adsorbing regions to enhance computational efficiency.
• Application of the method to compute Henry coefficients for CO₂, N₂, CH₄, and C₂H₂ in M-MOF-74 (M = Zn, Mg).

Main Results:

• The biased Widom insertion method significantly reduces the number of required single-point energy calculations (thousands vs. hundreds of thousands/millions).
• Accurate Henry coefficients were obtained for tested gases in M-MOF-74, showing good agreement with experimental data.
• DFT binding energy and heat of adsorption were found to be insufficient for ranking gas adsorption properties in the Henry regime.

Conclusions:

• The proposed biased Widom insertion method offers a computationally efficient and accurate approach for determining Henry coefficients.
• This method provides a valuable tool for screening and designing porous materials for gas adsorption applications.
• Relying solely on DFT binding energy or heat of adsorption is inadequate for predicting Henry regime gas uptake in porous materials.