Ab Initio Evaluation of Henry Coefficients Using Importance Sampling.

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Calculating Henry coefficients is crucial for understanding gas adsorption in porous materials.
• Current methods like Widom insertion require millions of energy evaluations, limiting the use of accurate ab initio calculations.
• Accurate force fields are often unavailable for complex guest-host interactions in materials like MOFs.

Purpose of the Study:

• To present a novel, efficient algorithm for computing Henry coefficients using ab initio energy calculations.
• To enable accurate simulation of gas adsorption in porous materials by reducing computational cost.
• To provide a more physically sound description of adsorption mechanisms compared to traditional force fields.

Main Methods:

• Developed a hybrid approach combining Widom insertion with importance sampling.
• Utilized force field simulations for initial configuration selection.
• Performed targeted ab initio energy calculations on selected configurations.
• Applied reweighting techniques to estimate the ab initio Henry coefficient.

Main Results:

• Reduced the number of energy evaluations by over an order of magnitude.
• Successfully applied the method to CO2 adsorption in Mg-MOF-74 and methane in UiO-66.
• Demonstrated the necessity of ab initio methods for systems with strong guest-host interactions.
• Highlighted the challenges in achieving accurate Henry coefficients due to varying theoretical levels.

Conclusions:

• The proposed method enables accurate ab initio Henry coefficient calculations at a moderate computational cost.
• Ab initio calculations offer superior physical insight into adsorption mechanisms compared to generic force fields.
• Accurate Henry coefficient prediction remains challenging, emphasizing the need for careful selection of theoretical methods and inclusion of effects like dispersion and many-body interactions.